Dead-Rail Transmitter/Receiver Options and Installation

Numerous wireless RF transmitter/receiver (Tx/Rx) options for locomotive control are available both in the US and abroad. My discussion is confined to wireless RF transmitter/receiver options that are DCC compatible, which means that the transmitter sends “logic-level” DCC packets, and the receiver converts the “logic-level” DCC packets back to “bipolar” DCC packets, as would be transmitted on tracks, that an onboard DCC decoder can “understand.”

Schematic of representative application

Why am I limiting my discussion? Because DCC is a standard, and if you don’t go with solutions that have standards behind them, then you are likely to suffer “vendor lock” where a single vendor holds you “hostage” with “their” solution. Perhaps that attitude is a bit overblown, but vendors with proprietary solutions tend to lag in innovation for lack of competition, and what happens if the vendor goes out of business?

I know that the NMRA DCC standards have some problems including the following issues: pending issues under consideration for years; vendors ignoring some parts of the standards; some vagueness in places; and lack of standards for wireless. The DCC standard is imperfect, but it’s miles better than no standard at all. Plus, the DCC decoder market is competitive and feature-rich – you can almost assuredly find a DCC decoder that will satisfy your needs.

As a further limitation of this post, I will mostly confine my discussion on DCC-compatible wireless Tx/Rx options to the 902-928 MHz ISM (Industrial, Scientific, and Medical) band because this is where I have direct experience. There is significant and exciting activity in the DCC-compatible 2.4 GHz ISM band (using Bluetooth technology) band as well (see BlueRailDCC), but I have no personal experience with this band. Another advantage of the 902-928 MHz ISM band is that there is some interoperability between transmitters and receivers, although there is currently no firm standard behind this interoperability.

DCC-compatible Tx/Rx options are a very large topic that I cannot fully cover in this blog. These options are well-covered in the following links:

  • Dead Rail Society: This should always be your first stop when looking at topics related to dead-rail. This site is the epicenter of dead-rail. In particular, this page discusses vendors for dead-rail Tx/Rx.
  • Facebook Dead Rail page: This social media page is a valuable source for the latest announcements and discussions for dead-rail, including Tx/Rx options.


Below is my personal experience with 902-928 MHz ISM DCC-compatible receivers.

General Comments

How each of these DCC compatible wireless receivers handles loss of valid RF signal from the transmitter is discussed here.

CVP Airwire

A CVP Airwire CONVRTR-60X wireless DCC-compatible RF receiver mounted to the side of the tender hull using Velcro. The U.FL antenna cable was later connected. The DCC “A/B” output of the CONVTR-60X connects to the “Track Right/Left” inputs of a wiring harness for a LokSound L V4.0 DCC decoder (not yet inserted) on the opposite side of the tender hull.

The company CVP manufactures and supports its Airwire series of products that include hand-held wireless DCC-compliant throttles (such as the T5000 and T1300) and receivers, such as the CONVRTR series that seamlessly connects to DCC decoders onboard the locomotive. As a general comment, CVP provides excellent, detailed installation and operation documentation, and that’s in part why they are dominant in some segments of wireless model railroad control. The CONVRTR receiver has some sophisticated features, such as setting its Airwire RF channel purely in software, that are described in its User Guide.

However, the CONVRTR interacts with the Airwire wireless throttles in ways that make it difficult to impossible​ to transmit just “garden variety” DCC wirelessly to the CONVRTR for proper operation. The Airwire throttles transmit numerous DCC “Idle” packets as a “keep-alive” message for the CONVRTR. A red LED on the CONVRTR board indicates received signal quality and flickers least when receiving a large number of DCC Idle packets. The brightness of the LED indicates the received RF power. Typical DCC throttles are not designed with these “keep-alive” concerns in mind, and do not output DCC Idle packets often enough to keep the CONVRTR “happy.”

Other than the CVP Airwire transmitters (the T5000 and T1300), the only RF transmitter that I am aware of that is capable of communicating with the Airwire CONVRTR is the ProMini Air, whose open-source software (at GitHub AirMiniTransmitter) intercepts “garden variety” DCC from the throttle and interleaves a sufficient number of DCC Idle packets to communicate correctly with the CONVRTR. This “keep-alive” requirement for the Airwire CONVRTR is challenging to produce, so sometimes a reset of the DCC throttle ​or the ProMini Air is required to initially send enough DCC Idle packets to initiate communication with the CONVRTR.

Like the Gwire receiver below, the Airwire CONVRTR “X” versions have a ​U.FL connector for connecting a shielded antenna cable from the receiver to an externally-mounted antenna. An internal antenna option is available as well for CONVRTR mountings that are not surrounded by metal.

QSI Solutions Gwire

Gwire U.FL connector. If using the U.FL connector, detach the wire antenna.

The Gwire receiver operates on Airwire RF channels 0-7, ​which must be selected from a dial on the device itself. A nice feature of this receiver is an onboard U.FL connector (see Figure above) that allows the user to connect a shielded antenna cable from the receiver to an externally-mounted antenna – useful when the antenna needs to be on the exterior of a metal locomotive or tender shell. See Blueridge Engineering’s website for details on how to interface the Gwire to any onboard DCC decoder. The Gwire presents no difficulties for wireless 902-914 MHz ISM band DCC-compatible transmitters, and it can be found on eBay at relatively low ($20 US or less) prices.

Tam Valley Depot DRS1, MkIII

Tam Valley Depot DRS1, MKIII in an open-cavity install. Note the built-in long wire antenna.

The Tam Valley Depot DRS1, MkIII receiver operates only on Airwire RF channel 16 (actually 916.49 MHz, which is close enough to Airwire channel 16 at 916.37 MHz) and makes a suitable wireless DCC receiver. This receiver has a long, single-wire antenna that provides efficient RF reception (see the figure above). However, this wire must be placed outside any metal shell, which may be inconvenient in some mounting applications. The DRS1, MkIII presents no difficulties for the 902-914 MHz ISM DCC-compatible transmitters as long as they transmit near 916.49 MHz. This receiver has been superseded by the DRS1, MkIV described in the next section.

Tam Valley Depot DRS1, MkIV

The recently-released Tam Valley Depot DRS1, MkIV receiver. Note the internal antenna on the right side of the board.

The Tam Valley Depot DRS1, MkIV receiver is a significant upgrade from the DRS1, MkIII, and operates at the original Tam Valley 916.49 MHz frequency, Airwire Channels 0-16, and at 869 MHz (for European operation). The DRS1, MkIV presents no difficulties for the 902-928 MHz ISM DCC-compatible transmitters and is an interesting choice because it changes channels automatically until it finds a sufficient RF signal carrying DCC packets. See the figure above for the version that employs an internal antenna that is useful when the receiver is not mounted inside a metal shell.

The DRS1, MkIV with a U.FL antenna connector (and a heatsink update) is now available (see picture below), making it very useful for connecting to external antennas outside of metal shells. This version of the DRS1 makes it highly competitive in capability and quality with the Airwire CONVTR. Perhaps future version will provide DC output to the onboard DCC decoder when no valid RF signals carrying DCC packets are available, making it possible to program the DCC decoder’s behavior when there is no DCC signal available.

Tam Valley Depot DRS1, MkIV receiver with U.FL connector.

Blueridge Engineering ProMini Air Receiver

The ProMini Air receiver. It uses an ATMEGA328P 16MHz 5V Compatible Arduino PRO Module and a Texas Instruments CC1101 transceiver PCB integrated on a Blueridge Engineering AirMini Pro PCB. Replace the antenna that comes with the CC1101-based PCB with a high-quality antenna or antenna cable.

The inexpensive ProMini Air receiver kit presents no issues when used with 902-928 MHz ISM DCC-compatible transmitters. It operates on Airwire RF channels 0–16 and requires a separate, low-cost amplifier (e.g., the Cytron MD13S) to convert the ProMini Air’s unipolar 5V DCC to bipolar DCC that provides sufficient power to the decoder. See the Blueridge Engineering web page for details on how to build the kit and properly connect the ProMini Air to the amplifier that is in turn connected to the onboard DCC decoder.

The ProMini Air’s open-source software is available for download at the GitHub site AirMiniTransmitter.


So far as I’m aware, there are four 902-928 MHz ISM DCC-compatible transmitters: the CVP Airwire T5000 and T1300, the Tam Valley Depot DRS1 transmitter, and the Blueridge Engineering ProMini Air transmitter.

CVP Airwire Transmitters

The CVP Airwire T5000 and T1300 transmitters are excellent choices for operating with 902-928 MHz ISM DCC-compatible receivers, all of which will properly-communicate with these two transmitters. When I am testing wireless receivers, the T5000 is my “go-to” because, in addition to serving as a DCC-compatible throttle, it can program onboard DCC decoders, via the wireless receiver, in either “OPS” (or Programing-on-the-Main, PoM) or “Service” mode. While the T1300 cannot program the onboard DCC decoders, it serves as a typical DCC throttle.

Of course, the Airwire transmitters send sufficient DCC “Idle” packets to keep the Airwire CONVRTR receivers “happy.”

Tam Valley Depot DRS1 Transmitter

The Tam Valley Depot DRS1 transmitter uses DCC packets produced by any DCC throttle or command station that outputs “bipolar” DCC to tracks. The DRS1 transmitter converts the “bipolar” DCC to “logic-level” DCC and transmits it at only 916.49 MHz, which is close enough to Airwire Channel 16 at 916.36 MHz to be received. This frequency limitation means that only the Tam Valley Depot DRS1, MkIII and MKIV; and the Blueridge ProMini Air receivers can operate with this transmitter if they are receiving on 916.48 MHz or Airwire Channel 16.

While the Airwire CONVRTR can operate on Airwire Channel 16, the DRS1 transmitter is not designed to transmit sufficient “Idle” DCC packets to keep the CONVRTR “happy” since it passively sends along only the DCC packets it receives from the DCC throttle or command station.

Blueridge Engineering ProMini Air Transmitter

The ProMini Air transmitter with optional LCD. The antenna in the picture was replaced with a high-quality 1/2-wave antenna Linx ANT-916-OC-LG-SMA antenna from either Mouser or Digi-Key for improved transmission.

Blueridge Engineering provides the ProMiniAir transmitter/receiver kit that uses open-source software at the Github AirMiniTransmitter site. Like the DRS1 transmitter, it is designed to take inputs from any DCC throttle or command station’s “bipolar” DCC output to tracks (via a simple, low-cost optocoupler provided by Blueridge Engineering) and transmit the “logic-level” DCC on Airwire channels 0-16.

The ProMini Air transmitter inserts a sufficient number of DCC “Idle” packets into the original throttle-produced DCC to keep the Airwire CONVRTR “happy.” This keep-alive capability coupled with transmission on Airwire channels 0-16 ensures that the ProMini Air transmitter is capable of communicating with any of the 902-928 MHz ISM DCC-compatible receivers discussed in this blog.

This transmitter’s settings, like channel number and output power, can be controlled by the DCC throttle or command station in the “OPS” mode by setting the throttle address to that of the ProMini Air, which is 9000 by default. An optional LDC display can be attached to the ProMini Air transmitter for status display. More configuration information is available at the GitHub AirMiniTransmitter site.

Full disclosure here: I am one of the contributors to the AirMiniTransmitter open-source software, and I have slightly helped Blueridge Engineering with the design of the ProMini Air transmitter/receiver board. But, I receive no financial compensation from Blueridge Engineering.

Dead-Rail Conversion of an MTH 2-8-8-8-2 Virginian Triplex


This post describes my most difficult dead-rail conversion to date: an MTH O scale 2-8-8-8-2 Virginian Triplex (MTH product number 20-3101-1) that I purchased on eBay circa September 2019. Previously, I converted a Sunset 3rd Rail Allegheny with an MTH Proto-Sound 3.0 board to dead-rail, but the Triplex was my first complete dead-rail conversion of an MTH locomotive to 2-rail operation, which included lathe turning high-profile wheels to approximate an NMRA RP-25 flange profile (also see NMRA standard S-4.2) so that the locomotive would operate reliably on track meeting NMRA standard S-3.2.

Box details
Locomotive side view
Tender side view

The inside view of the tender below demonstrates a significant challenge: space is very tight with the Proto-Sound board and the large speaker consuming a large part of the tender’s internal volume where we need to install additional dead-rail components: DCC-compatible RF receiver; 14.8V LiPo battery; and switch, charging, and antenna wiring.

Inside view of the tender: Note the battery cradle, the space-consuming speaker, and the end-of-tender smoke unit.

The strategy starts to emerge:

  1. Replace the Proto-Sound 2.0 (PS2.0) board with a PS3.0 board that can operate in DCC mode.
  2. Remove the original rechargeable battery and its cradle and locate the 14.8V LiPo battery pack there.
  3. Remove the large speaker and replace it with a smaller 4-ohm speaker so that we can make room for the 14.8V LiPo battery pack and the Airwire CONVRTR-60X DCC-compatible RF receiver that operates in the 902-928 MHz ISM band on Airwire channels 0-16.
  4. Lathe down the high-rail wheel flanges to approximate an NMRA “RP-25” profile for 2-rail, dead-rail operation.

An advantage of this strategy is retaining almost all of the control the PS2.0/PS3.0 provides, including directional head/tail lamp, marker lights, cabin lights, flickering firebox, sound, and fan-driven smoke units.

Proto-Sound 3.0 Conversion

The first step of the dead-rail conversion was easy: replacing the Proto-Sound 2.0 board with a Proto-Sound 3.0 (PS3.0) board from Ray’s Electric Trainworks. As I have mentioned in other posts, Ray Manley is a great person to work with. I sent my PS2.0 board as a trade-in to Ray, and he took care of the rest, providing me with a fully-functional PS3.0 board, complete with DCC capability.

The heatsink for the PS3.0 board necessitated drilling and tapping a new mount hole with spacer, as shown in the figure below.

New Proto-Sound 3.0 heatsink mount with a spacer.

The following photos show the original electrical power inputs to the PS2.0 board and their modified connections for the replacement PS3.0 board.

Original power connections to the Proto-Sound 2.0 board.

As you can see below, the AC power from the center rail pick-up (hot) and the outside rails (ground) were disconnected – we will be getting our power from a 14.8V LiPo battery pack in the tender. In this case, there is no Constant Voltage Unit, so no Battery +(14.8V)/Battery -(Ground) connections are required.

Locomotive power connection modifications. There is no Constant Voltage Unit in this locomotive, so the B+/B- wires indicated above are NOT used.

The AC power connections in the tender are also disconnected, and the power inputs to the PS3.0 connect to the switched battery power. The Battery +(14.8V)/Battery -(Ground) connection on the wiring harness was NOT required.

Tender power connection modifications. There is no need for B+/B- power supply to the locomotive.
Power input modifications for the PS3.0 board. The DCC A/B input power comes from the connection to the Airwire CONVRTR-60X DCC-compatible RF receiver.
Final wiring connections

Locomotive Electrical Modifications

There were two aspects to the electrical modifications in the locomotive:

  1. Headlamp replacement
  2. Electrical power supply

The original headlamp was a power-hungry incandescent bulb. An LED with a polarity-independent plug from Evan Designs was used to eliminate the need to determine the polarity of the original headlamp wiring.

Headlamp LED replacement details

The power-related modifications consisted of removing the center-rail pick-ups, which is very easy on MTH locomotives and disconnecting any wiring to the center-rail pick-up (hot) and the outside rails (ground).

The original center-rail pick-ups. The “Center-Rail Pick-up” is disconnected.
The center-rail connection underneath the motor is disconnected

Battery Installation

Battery installation was very challenging since the only practical placement location was the original rechargeable battery and its cradle mounting beside the PS2.0 board. A special-order 2x2x1 14.8V, 2600mAh (38.48 Wh, 5A rate,  LxWxT: 133 mm x 40 mm x 25 mm) LiPo battery purchased from provides the one cell-diameter thickness required to fit the battery pack between the PS3.0 board and the tender hull.

Original rechargeable battery and cradle location. The speaker volume control potentiometer was moved to accommodate the more extended 14.8 V LiPo replacement battery pack.
Volume control potentiometer. It was moved from its original location, and UV glue provides stress relief to prevent breakage of the very fine wires.
Final location of the volume control potentiometer. UV glue holds the potentiomenter in place.
Final battery location. Velcro attaches the battery to the side of the PS3.0 board.

Mechanical Modifications

In MTH steam locomotives, the wheel axles insert into a solid cast chassis frame, so the driver wheels must be pulled off the axle before machining the high profile wheels to approximate an RP-25 profile that is compatible with two-rail, dead-rail operation.

The driver wheels must be pulled off the axle for machining after removal of the side-rods. The axle and wheel are scribed to maintain proper “quartering.”
A wheel puller to separate the driver wheel from the axle.
Comparison of lathe-cut and unmodified high-profile wheels. The high-profile flanges were lathe-cut to approximate an RP-25 profile for 2-rail, dead-rail operation.

Tender Mechanical Modifications

The tender’s mechanical modifications involve adding a Kadee 740 coupler and accommodating additional dead-rail electronics.

Coupler Modifications

The original coupler pivot, rather than using a frame-fixed mounting, was used to mount a Kadee 740 coupler. This strategy ensured that tight curves would not bind the coupler.

The original coupler assembly

A Kadee 740 coupler was mounted on the original coupler pivot, as shown in the Figure below. The brass screw heads were ground down to provide clearance with the tender frame.

Modified coupler assembly for a Kadee 740 coupler

Additional Dead-Rail Electronics

The added dead-rail electronics include the charging plug, the ON/OFF/Charging plug, a smaller speaker, and the antenna mount.

Charging plug (left) and ON/OFF/Charge switch (right) mounting
Antenna mounting location. The antenna is a  Linx ANT-916-CW-RCS discussed in this blog.

The original speaker was far too large to provide clearance for the additional battery, DCC-compatible RF receiver, and other electrical components needed for the dead-rail installation. So a 16mm x 35mm speaker was placed in the bottom of the original speaker’s cavity, and UV glue holds the speaker in place.

The original speaker. It is far too large to accommodate the additional dead-rail components: battery, DCC-compatible RF receiver, ON/OFF/Charging switch and charging plug.
Candidate speaker. The actual 16mm x 35mm speaker was even smaller and mounted into the bottom of the original speaker cavity.

Final Demonstration

With the locomotive reassembled, it’s time to test it out! If your locomotive has a smoke unit(s), always ensure sufficient smoke fluid is loaded. Even if you don’t intentionally turn on the smoke unit – sometimes it’s unexpectedly activated.

Initial demonstration

Dealing with Loss of RF Signal in Dead-Rail for Onboard DCC Decoders

Note: This post deals with details of various brands of DCC-compatible, wireless RF receivers operating in the 902-928 MHz “ISM” band that connect to onboard DCC decoders. Some aspects of the discussion may apply to other RF bands as well.

Typical application. In some cases, such as the Airwire transmitters, the throttle and transmitter are combined. Also, the receiver and amplifier may combined, such as for Airwire and Tam Valley Depot receivers.

The designers of various DCC-compatible RF receivers have a couple of strategies for what output to provide to the onboard DCC decoders when a valid RF signal is lost:

  1. Output the random pulses that the RF receiver naturally outputs when a valid RF signal is lost. This option will cause most DCC decoders to maintain direction and speed while the DCC decoder “sifts” the random pulses searching for valid DCC packets.
  2. Output a fixed, positive Direct Current (DC) voltage to one of the DCC decoder’s “Track” inputs and a zero voltage DC the other “Track” input when either RF signal is lost or, for some RF receivers such as the Airwire CONVRTR, if insufficient “keep-alive” DCC packets are not received from the RF transmitter. How the DCC decoder responds to these DC “Track” inputs depends upon DCC decoder configuration and, unfortunately, DCC decoder manufacturer discretion.

There are several NMRA-specified Configuration Variables (CV’s) that affect how DCC decoders handle the loss of valid DCC packets and are important to understand when the DCC decoder is connected to the DCC output of DCC-compatible RF transmitters because the RF receivers may lose or receive corrupted RF signal from the dead-rail RF transmitter.

The NMRA standard S-9.2.4, section C “Occurrence of Error Conditions” states “Multi Function Digital Decoder shall have a Packet Update time-out value.” Further down on line 60 the standard states “A value of 0 disables the time-out (i.e., the user has chosen not to have a time-out)”. This part of the NMRA standard is not universally-implemented by manufacturers, and it affects how decoders will respond to the loss of RF transmission of DCC packets. To implement this requirement, the NMRA standard S-9.2.2 has defined the recommended (R), but not mandatory (M), CV11, Packet Time-Out Value. A value of CV11=0 is defined to turn off the time-out, but CV11 is frequently not implemented.

However, another CV that is often implemented addresses some aspects of loss of DCC. The optional (O) CV27, Decoder Automatic Stopping Configuration, is under re-evaluation by NMRA, but the NMRA has taken no definite action some time. Here is what the NMRA standard S-9.2.2 currently (as of 2019) states about CV27: 

Configuration Variable 27 Decoder Automatic Stopping Configuration
Used to configure which actions will cause the decoder to automatically stop.

Bit 0 = Enable/Disable Auto Stop in the presence of an asymmetrical DCC signal which is more positive on the right rail.
“0” = Disabled “1” = Enabled

Bit 1 = Enable/Disable Auto Stop in the presence of an asymmetrical DCC signal which is more positive on the left rail.
“0” = Disabled “1” = Enabled

Bit 2 = Enable/Disable Auto Stop in the presence of an Signal Controlled Influence cutout signal.
“0” = Disabled “1” = Enabled

Bit 3 = Reserved for Future Use.

Bit 4 = Enable/Disable Auto Stop in the presence of reverse polarity DC.
“0” = Disabled “1” = Enabled

Bit 5 = Enable/Disable Auto Stop in the presence forward polarity DC.
“0” = Disabled “1” = Enabled

Bits 6-7 = Reserved for future use.

Since DCC decoder manufacturers frequently do implement CV27, what electrical output the DCC-compatible RF receiver provides to the DCC decoder upon loss of a valid RF signal will influence how the DCC decoder responds. We will break this down for various brands of DCC-compatible RF receivers in the 902-928 MHz ISM band in the following subsections.

Note that some DCC decoders will not honor CV27=0; i.e., all auto-stopping features disabled. For example, with CV27 set to 0, the Zimo MX-696, and probably other Zimo DCC decoders as well, will continue speed and forward direction if positive DC level is input to the “Right Track” DCC input, and a zero DC level is input to the “Left Track” DCC input. Under these “track voltage” conditions, the locomotive will stop if originally moving backward. Some (but not all) DCC-compatible RF receivers, such as the Airwire CONVRTR, provide these DC inputs, if a valid RF signal is lost, but only if connected correctly.

The “correct” connection relates to how the user connects the DCC output from the RF receiver to the “Track Right” and “Track Left” inputs of the DCC decoder. Under normal circumstances, when there is a valid RF signal, which way the DCC decoder connects to the RF receiver does not matter. Under the exceptional case of DC-only output by the RF receiver, if it loses a valid RF signal, which way the DCC decoder connects to the RF transmitter does matter. The user will likely want the locomotive to continue forward with the loss of a valid RF signal, so some experimentation is required to determine which of the RF transmitter DCC outputs should connect to which of the DCC decoder’s “Track” inputs to achieve the desired behavior.

Example DCC waveform output from a DCC-compatible RF receiver when there is a valid RF signal
Example random pulse output from a DCC-compatible RF receiver when there is no valid RF signal. Note the waveform’s superficial similarity to valid DCC output.

As a further complication, the user should probably turn off the decoder’s “analog” mode of operation by setting Bit 2 of CV29 to 0 to force the decoder to use “NMRA Digital Only” control of ”Power Source Conversion” (see the NMRA standard here). If Bit 2 of CV29 is set to 1, and again we emphasize the user should probably not activate this feature, then “Power Source Conversion Enabled” and then CV12 determines the power source; the most common of which is CV12=1, “Analog Power Conversion.”

Airwire CONVRTR Series

CVP Airwire CONVRTR-60X tender installation. The CONVRTR operates on Airwire channels 0-16. Note that the U.FL antenna lead was later connected to the CONVRTR. The LokSound L V4.0 DCC decoder mounting harness can be seen mounted on the tender wall opposite the CONVRTR, and its Track Left/Right inputs are connected to the CONVRTR-60X’s DCC A/B outputs.

When the CVP Airwire CONVRTR loses a valid RF signal or receives insufficiently-frequent DCC Idle packets, it detects these conditions and outputs a fixed DC voltage to the decoder. Consequently, the user should set CV27 according to the description above.

While it may seem that the user would want the locomotive to stop if its RF receiver loses a valid RF signal, consider what might happen in tunnels or locations remote to the DCC RF transmitter. Getting stuck under these circumstances if a valid RF signal is lost is probably not what the user wants, so we strongly suggest that the user set CV27=0.

The user is cautioned, however, that some DCC decoders, such as the new ESU LokSound 5 L DCC, do not honor the CV27=0 setting unless the “polarity” of the “Track Right/Left” is connected “correctly” to the CONVRTR’s “A/B” output. Experimentation may be required to determine the correct connection, but my experience is: CONVRTR A <–> Decoder Track Right & CONVRTR B <–> Decoder Track Left

QSI Solutions Gwire and Tam Valley Depot DRS1 Series

The QSI Solutions GWire operates on Airwire Channels 0-7. If the U.FL plug (at the upper-left corner of the Linx Transceiver chip) connects to an externally-mounted antenna, the antenna wire at the upper-left corner of the GWire board should be cut off at board level, or better yet, unsoldered.
The Tam Valley Depot DRS1, MKIII, operates on Airwire Channel 16
The Tam Valley Depot DRS1, MkIV, operates on Airwire Channels 0-16 (as well as other frequencies). Note the internal antenna on the right-hand side of the board.

The QSI Solutions Gwire and Tam Valley Depot DRS1, MkIII and MkIV DCC-compatible RF receivers will output random pulses to the onboard DCC decoder when a valid RF signal is lost, so setting CV27 is probably of no use. On the “plus” side, most DCC decoders will maintain locomotive direction and speed in the presence of these random pulses since the DCC decoder is actively sorting through these pulses for valid DCC packets, which is usually the behavior the user wants.

A Blueridge Engineering webpage describes how to easily modify the GWire for use as an RF receiver for any onboard DCC decoder.

Blueridge Engineering ProMini Air Receiver

Blueridge Engineering ProMini Air receiver operates on Airwire channels 0-16. The ProMini Air can also be configured to operate as a DCC-compatible transmitter that wirelessly transmits DCC from any DCC source on Airwire channels 0-16.

The Blueridge Engineering ProMini Air receiver has a default long address of 9001. Like the ProMini Air transmitter, the ProMini Air receiver’s channel can be reset in “OPS Mode” by setting CV255 to a value in the range of 0–16. The ProMini Air receiver has the following options when a valid RF signal is lost:

  • Output random pulses to the onboard DCC decoder: The user can set the ProMini Air receiver to output the random pulses when it loses a valid RF signal by setting CV246  to 0 in “OPS mode” at the ProMini Air’s address. In this case, setting CV27 for the onboard DCC decoder is not relevant, because the random pulses from the ProMini Air receiver will cause the on-board DCC decoder to maintain speed and direction of the locomotive while it is “sifting” through the random pulses for valid DCC packets.
  • Output either fixed positive or negative voltage DC to the onboard DCC decoder: In this case, setting CV27 for the onboard DCC decoder at its address is relevant. The user can set the ProMini Air receiver to output fixed DC voltage when it loses a valid RF signal by setting CV246 to 1 in “OPS mode” at the ProMini Air’s address. A positive DC voltage is output by setting the ProMini Air receiver’s CV248 to 1 in “OPS mode” at the ProMini Air’s address, or a negative DC voltage is output by setting CV248 to 0. If the user does not want the locomotive to stop with the loss of a valid RF signal, then set CV27=0 for the onboard DCC decoder at its address. Of course, setting CV27 to other values (see above) in the DCC decoder will determine how the DCC decoder responds to the fixed DC voltage that the ProMini Air outputs to the onboard DCC decoder upon loss of a valid RF signal.


It’s an unfortunate fact of life that we can lose a valid RF signal from our DCC-compatible transmitter. However, with a little study of DCC decoder documentation, and possibly a bit of experimentation, gracefully coping is definitely possible.

Retro-Fitting Smoke Units with Thermistors and Set-up for LokSound Decoders

This is a slight modification of a post I made titled: O Gauge Forum Post on Smoke Units

It is possible to modify a non-ESU smoke unit so that it connects to the LokSound L or XL decoders just as an ESU smoke unit does by connecting the smoke unit to the specialized ESU smoke unit terminals: HTR+/-, MOT+/-, and TMP+/-. This capability allows you to take direct advantage of all the LokSound capabilities provided for ESU smoke units. The missing component in some smoke units is a Negative Temperature Coefficient (NTC) thermistor.

What started me down this road was a “deadrail” conversion of a Sunset 3rd Rail Big Boy (3-rail, “Late Version”) originally outfitted with TMCC and a nice Lionel smoke unit with dual output (photo below).

Dual stack, fan-driven smoke unit for retro-fit.

I wanted to retain this beauty and use a LokSound L V4.0 decoder that is controlled by an Airwire CONVRTR-60. THOR73’s posts on the O Gauge Form inspired me to work through using this smoke unit with the LokSound L V4.0 decoder. I thought that if I could figure out how the ESU smoke units created their “temperature” inputs to the LokSound decoder, then I could retrofit the Lionel smoke unit so that it would be “input compatible” with an ESU smoke unit. This retrofit turned out to be simple.

I reverse-engineered an ESU 54678 smoke unit by measuring the resistance between the heater resistor leads (HTR+/-): ~23 ohms; motor leads (MOT+/-): ~16 ohms; and thermistor leads (TMP+/-): ~100K ohm at room temperature. Each of these components is electrically-isolated from the others. When powered by a 14.8V LiPo battery, the LokSound L V4.0 decoder I had on hand produced the following results on the ESU Profi board using the LokProgrammer (with ground measured at the Profi board’s ground terminal):

Terminal Smoke off Smoke on (Throttle=10)
HTR+ (not connected to heater resistor*) 13.4V 13.2V
HTR- Open Switched open/ground @500Hz ~30% duty-cycle PWM
Fan+ 0V Pulsed <= 5V (difficult to determine with low Frequency chuffs)
Fan- 0V 0V
TMP+ 5.1V 5.1V
TMP- 1.3V 3.7V
* Battery+ (14.8V) connected to heater resistor + input

The difference in TMP- between unheated and heated conditions suggests, but does not prove, that the thermistor’s decrease in resistance with increased temperature is manifested by a voltage increase at TMP- as part of a voltage divider where the thermistor is in series with a fixed resistor resident in the decoder, possibly with a low-side voltage offset:

Probably thermistor circuit

Guesses: RFIXED~1.5K based on probe measurements and derived @ 25C Voffset~1.24

So right off the bat, the ESU smoke unit’s heater resistance (23 ohms) is similar to Lionel’s (27 ohms), and both smoke units use 5V fan motors. The Lionel was missing only the thermistor. Lower resistance smoke units (around 8 ohms) might be problematic to convert unless retrofitted with a heater resistor in the 20 ohm neighborhood or use an externally-supplied, lower HTR+ voltage. The heater and fan motor similarity between the ESU and Lionel smoke units seemed to make this particular Lionel smoke unit an excellent surrogate candidate.

Thermistors with 100K ohm resistance at 25 Celsius are commonly-available, usually with a “B” parameter of around 3900 Kelvin. You can Google what this parameter means (simplified Steinhart-Hart Equation: R(T in Kelvin)=R@TRef*(exp(B/T-B/TRef)) ). While I was not able to verify that the ESU smoke unit used precisely this type of thermistor, testing described later supports this selection.

The photo below is the Lionel 27 ohm smoke unit PCB, part #610-PCB1-045, Rev C (Lionel replacement part #691PCB1045), that was retrofitted with an “axial,” glass-coated 100K NTC thermistor with a B of 3892 Kelvin. (Well, it’s actually a Lionel replacement PCB since I cut some traces retrofitting on the original PCB that I regret doing. Interestingly, the original PCB did not have the mangled lettering of the replacement PCB that some like some have noted.)

The 3-pin power plug on the PCB can be used to power the heater resistor since the outputs from the rectifier/5V converter on the PCB do not connect to anything after removing the fan motor plug. The ground on the PCB MUST be isolated from the heater unit metal case since the PCB’s “ground” wire will be connected to the LokSound L’s HTR- terminal that regulates the heating resistor’s current path to ground! Electrical measurements revealed good electrical isolation of the metal case from the heating element.

Lionel fan-driven smoke unit with a 100K thermistor added.

Two holes were drilled in the smoke unit’s PCB board, and the thermistor was inserted and soldered to two wire leads that connect to the LokSound L’s TMP+/- terminals. High melting-point solder was used in the off chance that conventional solder might melt at the high operating temperatures of the heater resistor and thermistor (max around 250 Celsius according to documentation for the ESU smoke unit). 

The two heater wires from the three-pin PCB plug connect to the LokSound L’s HTR+/- terminals. (Pins 1 and 3 are shorted together on the PCB and connect to one side of the heater resistor. Pin 2 is ground and connects to the other side of the heater resistor.)

The motor wires directly connect to the MOT+/- terminals. Out of sheer luck, when the red motor lead from the smoke unit is connected to MOT+, and it’s black lead to MOT-, the fan motor spins in the “correct” direction.

As others has suggested, I also replaced the original 27 ohm ceramic resistor with a Lionel 27 ohm replacement #6008141055

Once the smoke unit’s six outputs were connected to the LokSound L’s ESU smoke unit terminals, there were some modifications needed in the ESU sound files and decoder set-up, since they did not originally activate the ESU smoke unit. First, follow THOR73’s directions regarding the connection between sound and smoke chuffing under the “Smoke unit” menu. Note especially that the smoke unit’s automatic power-off time should be reset since the default is 0 seconds. I don’t know if 0 means never turn off, but a non-zero setting seemed like a good idea to me.

LokSound change decoder settings menu

What differs from THOR73’s discussion is the sound-file set-up for an ESU smoke unit. Editing the sound files reveals that most “nodes” have an option to set the “ESU Smoke Unit” parameters. Frequently these settings are turned off, but there are some useful “presets” you can select and experiment with.  An especially interesting preset is the “preheating” preset that is available in the stopped state.

Mute State:

LokSound Stop state settings.

Here are the other states I modified, but I am by no means expert or knowledgeable about these settings. Usually, I chose a “Preset” and then selected the “Steam Chuff” checkbox, which preserves the parameters of the preset (unless you change them), but turns off the Preset name.

Stop State:

LokSound Mute state settings

DCX State:

LokSound DCX state settings

Coast State:

After editing these sound nodes, the next step is to set an “F#” to turn the smoke unit on/off on the “Function mappings” menu. The “logical” outputs column provides an “ESU Smoke Unit” selection, so I selected F23 as the ESU Smoke Unit on/off toggle.

A TESTING WARNING: The ESU 53900 Profi Decoder Tester does not appear able to provide adequate power to either an actual ESU Smoke Unit or surrogates described here! In actual operation, the LokSound L is perfectly capable of providing sufficient power, but the Profi board is, in my experience (or inexperience), NOT able to do so. I initially thought the culprit was the puny AC to DC converter provided to power the Proof board, but power connection to a very hefty 14.8V LiPo battery did not solve the problem. The workaround is to use either THOR73’s high-side MOSFET switch mentioned in this thread or use the low-side MOSFET switch described in the same thread. Either way, you will need to take power (about +14V DC) from the source providing power to the Profi board and use the Profi board’s HTR- output to control the MOSFET switch that will, in turn, control the smoke unit’s heater. If using THOR73’s high-side switch, then you connect the smoke heater as he describes. If using the low-side switch I presented, the smoke unit’s HTR- connects to the switch control input, and the switch’s ground connects to power ground. 

Reiterating, THIS SPECIALIZED MOSFET SWITCH IS ONLY NEEDED FOR TESTING WITH THE Profi BOARD! In actual operation, the LokSound L is designed to adequately power an ESU smoke unit by direct connection to the decoder’s ESU smoke unit terminals, as is the modified smoke unit described here. 

Here’s the “proof in the pudding” video:

Surrogate smoke unit in action

Please forgive the disassembled state. I haven’t finished the deadrail conversion, but this video does demonstrate battery power with the LokSound L V4.0 controlled by an Airwire CONVRTR-60 wireless receiver.

Follow up

To be pretty linear, my guesses on RFIXED and Voffset are 1.5K and 1.24V. The 1.5K came from an “off” measurement of resistance between decoder GROUND and TMP-, which is fraught with potential for error.

These will give you the following approximate curves where the left axis is the voltage at TMP-, and the right axis is the estimated thermistor resistance.


Example thermistor T versus V and T versus R curves

Common Aspects of 3-Rail to Dead-Rail Conversion of O Scale Steam Locomotives


After doing about eight or so O scale 3-rail to dead-rail conversions for steam locomotives, some similar features pop out that I will discuss in this blog. As with my other O Scale Dead Rail blogs, I will try to stick mostly to my own experience.

A note of caution: O scale steam locomotives are expensive, and some, to me, are works of art. Consider very carefully whether you have the patience and skill required to make locomotive conversions. I got into O scale dead-rail conversions to teach myself patience, a few skills, and respect for these beautiful models. Give yourself plenty of time to make these kinds of conversions – being in a hurry is a prescription for trouble – I know because I sometimes got in a hurry. Just don’t.

There are some good tutorials on locomotive repair and disassembly. I recommend this one as a good place to start.

General Considerations

Good grief, what do “general considerations” mean? Well, it’s the general aspects that guide the conversion process for both the locomotive and the tender.

First, most, but not all, of my O scale 3-rail to dead-rail conversion experience is with Sunset 3rd rail steam locomotives: Big Boys, Cab Forwards, Challengers, and Alleghenys, so first off you see that I’m an articulated locomotive fan. Articulated locomotives (AL) can be challenging to dis-assemble, and, especially, re-assemble. Heck, they are tricky to handle correctly especially since the front driver chassis must in some way “float” to navigate modest-radius curves.

In general, even though 3-rail locomotives pick up AC from the track, the locomotive motors are almost always DC motors, where the DC power is usually supplied via a connector from the tender. Usually (always in my experience), the two outside rails are electrically connected to the locomotive chassis, and the AC power from the center roller pickups completes the power loop, fully isolated from the locomotive chassis.

This outside/center AC power inputs are typically supplied to the tender from the locomotive via the same connector to provides DC power from the tender back to the locomotive motor. So right off the bat, you have some bad news and some good news:

  • Bad news: We will need to eliminate the physical and electrical connections to the center-rail AC picked up by the center pickup shoes from the locomotive to the tender because we’re not using rail power in dead-rail. This will be accomplished by removing the center rail pickup shoes and, just to be on the safe side, eliminating all of the center-rail AC wiring. In theory, once the pickup shoes are removed, all center-rail AC wiring is isolated electrically, but I don’t take any chances, and I just remove all of the center-rail AC wiring.
  • The good news about the bad news: We can re-purpose the center-rail AC power plug connection between the locomotive and tender (originally sending center-rail AC power from the locomotive to the tender), and instead we send Switched Battery+ from the tender to the locomotive to provide power to the Constant Voltage Unit that distributes power to components such as smoke units, marker lights, and sometimes the headlamp.
  • Good news: The locomotive’s chassis “ground,” which is electrically connected to the outside rails via the locomotive wheels, does not require electrical connection modification – all we’re going to do is ensure that chassis ground is connected to the tender’s Battery- (Ground) through the original locomotive-to-tender plug. The Battery- (Ground), as the name implies, is also connected to the tender chassis ground.
  • Good news: It’s easy to get the DC power from the tender to the locomotive’s motor(s) through the original locomotive-to-tender plug without modifications to the locomotive motor’s electrical connections.
Figure 1: Typical locomotive/tender connector pin-out for Samhongsa (Sunset 3rd Rail, Williams) locomotives

Another unique aspect to 3-rail locomotives is the reversing board in the tender that converts the AC power coming from the locomotive to a correctly polarized DC voltage for forward/reverse motion depending on the pattern of interruption of AC to the locomotive. I am not an expert on reversing units – I am in the business of removing them for dead-rail operation. If the locomotive has sound, the sound electronics/card is usually highly integrated (meaning not DCC-compliant) with the reversing unit, which means that we must provide a DCC-compliant replacement sound card of full DCC decoder with sound since the radio-controlled receiver boards “speak” DCC in most cases. Removal of the original sound electronics is a shame because it may have some unique/interesting audio we’d like to reuse. If I ever figure out how to re-use the sound from these original sound units, that will, of course, be another blog. My initial attempts to obtain legacy (remember these cards are sometimes over fifteen years old) circuit interface information from OEM sound card manufacturers such as QSI Industries have not been fruitful, even though they were friendly.

Locomotive Conversion

All of the 3-rail O scale steam locomotives I have converted to dead-rail had the following aspects of conversion that will be discussed in the next three sections: center pickup removal, lighting modifications, and various electrical modifications. Three-rail locomotives are somewhat more challenging than 2-rail to convert because of the unique aspects of power pick-up using the third, center rail.

Center Pickup Removal

Removal of the center pickups involves both the rollers themselves and the electrical connections to them. I remove the locomotive pickup rollers because we will usually operate the locomotive on two rails, even though they are unpowered. I suppose you could leave the rollers in place, but this would restrict dead-rail operation to dead 3-rail track. In summary, I think removing the rollers gives you more operating flexibility for dead-rail operation.

See the Figure below for an example of how to remove the undercarriage baseplate so that you can remove the rollers.

Figure 2: Center pickup roller removal

Unfortunately, the undercarriage baseplate requires removal to get at the center pickup roller mounting screw. This plate is usually held in place by six to eight retention screws, but even when you remove them, you have several issues:

  • Often you cannot remove the plate without catching the brake shoes on the drivers. You can solve this problem by removing the brake shoes from one side and sliding the base plate sideways to free to brake shoes on the other side.
  • The wiring underneath the plate connecting to the pickup rollers does not have sufficient slack to allow lifting the cover. You have two options: carefully slip a wire cutting tool in the narrow space between the freed baseplate and the rest of the chassis, or remove the entire wheel chassis from the boiler section and cut the wires from above. See the Figure below. You still need to remove the baseplate to unscrew the center pickup rollers because you cannot get to them even with the wheel chassis separated from the boiler section.
Figure 3: Center pickup roller wiring modifications. The Constant Voltage Unit is part of an MTH Proto-Sound 3 dead-rail conversion for a Sunset 3rd Rail Allegheny.

Once the baseplate is freed from the rest of the chassis, then it’s a snap to unscrew the roller from the baseplate and to cut/remove any connecting wiring. Usually, I also remove the insulator pad screwed into the baseplate.

Once all of this is done, then, of course, you remount the baseplate and any temporarily-removed brake shoes.

Note: Care is required to remove and replace the baseplate. The spring-loaded driver bearings are held in place by the baseplate, imparting significant spring force on the baseplate, which will bend the baseplate unless the retaining screws are eased in and out uniformly. Slight bending is OK but significant, local kinks are bad. Also, these bearings can easily pop out of place, so inspection is required to ensure the bearings are properly-seated before tightening down the baseplate.

Lighting Modifications

Steam locomotive lighting includes some or all of the following:

  • Headlamp
  • Marker lights
  • Cabin lights

We’ll discuss each of these in turn


The headlamp is special because we usually want to control its on/off automatically as the locomotive changes direction and possibly according to “Rule 17” which dims the headlamp and tail lamp according to whether the locomotive is stationary (dim) or moving (full brightness).

In my experience with Samhongsa locomotives (Sunset 3rd Rail and Williams), the headlamp is powered by one of two means:

  1. A separate, small rectifying board. It is powered by AC from the center rail and AC from the outside rails and turns on/off power to the headlamp as the locomotive moves forward/backward. This technique is typical of older Williams locomotives.
Headlamp direction board in a Williams UP Challenger. It must be disconnected from the headlamp since the track AC is not used to power the headlamp.
Figure 4a: Williams locomotive circuit diagram showing the Constant Voltage Unit, its voltage regulator, and headlamp direction board

The headlamp direction board is removed and the two leads  to the headlamp are connected to the tender via a separate two-wire connector to the tender’s Switched Battery+ and the receiver’s headlamp control output, which, for example, is Pin TM1-1 on a CVP Airwire G3 decoder (see page 17, G3 Decoder User Guide). The receiver/decoder board will then determine the locomotive direction and control the headlamp accordingly.

  • An output on the Constant Voltage Unit. In this case, the power from the CVU to the headlamp is cut, and power to the headlamp is replaced with a two-wire connector as described in the previous case. Of course, you should directly trace the wires to the headlamp before you cut any wires. This arrangement is typical of Sunset 3rd Rail locomotives. See the Figure below. When I first started these conversions, I was super-conservative and electrically isolated the CVU from the chassis and made a direct, wired connection to the Battery- (ground) as shown in the Figure below. But, using chassis ground, which will be electrically connected to the tender’s Battery- (ground) through the loco to tender plug has worked out OK.
  • Sunset_3rd_Rail_Challenger_Headlamp_Mods
    Figure 4b: Modifications to the headlamp electrical connections for Sunset 3rd Rail locomotives. The replacement of chassis ground by the direct wired connection to Battery- (ground) is unnecessary. See Figure 4a for more details on how the CVU is connected.

    Marker Lights

    Marker lights are almost always LED’s whose power is supplied by the Constant Voltage Unit. No modification of the wiring from the CVU to the marker light LED’s is necessary since once power is supplied to the CVU, then it will in turn properly supply the marker light LED’s.

    Smoke Units

    As with the marker lights, once power is supplied to the CVU, then the CVU is designed to supply the proper power to the smoke units. A switch is always mounted on either the locomotive or the tender to turn on/off the smoke unit. No smoke wiring modifications are required.

    All of the smoke units controlled by CVU’s in my experience are Seuthe smoke units, typically requiring 6V DC. They have the disadvantage that they do not “chuff” in coordination with steam locomotives’ piston action. Replacement of these venerable, but unrealistic smoke units with smoke units that contain a “fan” that propels the smoke in synchronization with the sound chuffs from Lionel, ESU, or MTH is a big topic that will be covered in another blog.

    An ESU 54678 fan-driven smoke unit that is appropriately-sized for O scale and is designed to work in tandem with ESU LokSound decoders such as the LokSound L.
    An ESU 54678 smoke unit with additional brass tubing to be installed in a Williams UP Challenger
    A preliminary position install of an ESU 54678 smoke unit in a Williams UP Challenger to determine if the ESU LockSound L V4.0 decoder would fit behind the smoke unit. This smoke unit has two connections each for the heater, fan motor, and thermistor. The thermistor provides a temperature measurement of the heater to the LokSound L’s sensing circuitry that will carefully control the temperature.
    Detail of the Williams UP Challenger smoke stack with smoke unit tubing. The original Seuthe smoke units were cut to retain only the funnel that was fit over the smoke unit’s brass tubing. Care is taken to ensure the smoke fluid is inserted directly into the brass tubing.
    A Lionel 610-8057-200 fan-driven smoke unit I have used for O scale installations.

    The smoke unit pictured below is very similar to the Lionel 610-8057-200 smoke unit pictured above. It was retro-fitted with a 100K thermistor to emulate the ESU smoke unit inputs for a LokSound L V4.0 decoder.

    A smoke unit almost identical to the Lionel 610-8057-200 with modifications. All of the original electrical components have been removed and a connecting trace was cut to isolate the Heater Resistor +/- from the Fan Motor +/-. Liquid tape was applied to the smoke funnel lip to enhance mounting friction and improve sealing. A 100K thermistor was installed adjacent to the 27 ohm heating element to emulate the ESU smoke unit inputs to a LokSound L V4.0 decoder.
    A smoke unit almost identical to the Lionel 610-8057-200 unit installed in a Sunset 3rd Rail Allegheny with a custom brass mounting bracket.
    An MTH AA-0000070 fan-driven smoke unit that is well-sized for O scale.
    The MTH AA-0000070 smoke unit pictured above with custom brass brackets for mounting in a Sunset 3rd Rail AC-6 Cab Forward. The small size of this smoke unit is well-suited to the tight fit afforded by this locomotive. This smoke unit has no thermistor, so it easily interfaced to the Zimo MX-969KS decoder installed behind the smoke unit. This decoder is ideal for O scale installs because of its narrow form factor.
    A Zimo MS696KS DCC decoder and screw-terminal board. The decoder’s slim design and well-documented connections for fan-driven smoke units makes it a good choice for O scale installs. “Ventilator” (which turns on/off 5V to the motor) and Ground are used to turn on/off the smoke unit’s fan, and +Power and any of the Zimo’s “FA” connections, which are software-controlled switches to open/close a connection to ground, controls turning off/on the smoke unit’s heating element.

    A final note of caution on smoke units: When using smoke units with metal cases, it’s crucial to ensure that the heater element (resistor), fan motor, and thermistor (if there is one) are completely electrically-isolated from the metal casing that will be in firm contact with locomotive ground. You should absolutely verify this with an ohm meter. If you don’t check each lead to verify there is no short to the smoke unit case, you will be sorry. I have forgotten twice (I learn slowly sometimes) to check for electrical isolation of these components from the smoke unit case, and I poured amps from a battery in the tender to the locomotive along a direct path from Battery + to Battery – (ground), melting lots of wiring along the way. This error will cost you hours of work and possibly dozens to hundreds of dollars in damaged electronics.

    Original Equipment Manufacturers (OEM’s) often made a point of ensuring good ground contact to some of the smoke unit components – we don’t want this. We want the decoder (or the RF receiver if its handling smoke unit control) to handle how these components are electrically-routed to ground! Yes, these components all need power which we frequently supply from a common source, but it’s the route to ground that we want to carefully control.

    As a side note, pay careful attention to the voltage requirements of the smoke unit components. The heating element and motor almost always are supplied with different voltages! I have never seen a smoke unit motor that didn’t require 5 Volts. I have inadvertently killed one of these cute little motors by accidentally supplying it with 14.8V.

    The heating element’s voltage depends very much on its resistance (they vary from 6 ohms to 28 ohms) and interaction with the electronics that controls it, such as a DCC decoder or an Airwire RF receiver such as the G3. You need to carefully understand the specs of the heating element and the device that will control it. Spend some time reading. As a general rule, you tend to stay out of trouble with higher resistance heating elements because for a fixed supply voltage, the power produced by the heating element is inversely-proportional to the resistance (remember: Power = (V*V)/R, where Power is in Watts, V is in Volts, and R is in Ohms).

    Even if you are within the proper voltage supply range for a smoke unit, you can still burn them up under certain circumstances. Pay heed to the dark warnings that you should always run your smoke unit loaded with the proper amount of smoke fluid. As the fluid evaporates, it cools the heating element – no fluid and the heating element and the specialized batting that wicks the smoke fluid into contact with the heating element will get hotter. Often, it’s the wick that gets scorched with too high temperatures and/or no smoke fluid, and this scorching damages the wicking action.

    Example of a fan-driven smoke unit’s wick (in the left chamber)

    That’s why some some smoke unit manufacturers, such as ESU, use thermistors to measure the heating element’s temperature and send this information to the decoder so that it in turn can adjust the voltage to the heating element to prevent burn-up. So far as I know, only ESU DCC decoders have thermistor inputs for this smoke unit feedback control. I have reverse-engineered an ESU smoke unit and found that it uses a 100K thermistor that can be easily purchased and retro-fitted into other smoke units if you intend to use the smoke unit with ESU decoders. High-melting point solder must be used when adding a thermistor. Lacking that decoder feedback control of the smoke unit’s heater, I have devised a compact temperature feedback control, but that’s for another blog…

    Lionel fan-driven smoke unit with a thermistor retro-fit for use with a LokSound L V4.0 DCC decoder. High melting point (HMP) solder should be used when soldering thermistors or replacement resistors on smoke units. (Note the munged “Lionel” name on the board. It’s a genuine Lionel board, but I doubt it was “MadoinUOA”.)

    Electrical Modifications

    Constant Voltage Unit

    We have already discussed the Constant Voltage Unit (CVU) a bit under the section dealing with headlamp modifications. Some locomotives have a Constant Voltage Unit (CVU) that converts AC power from the outside rails/chassis (ground) via the locomotive wheels and center-rail AC via the center pickup shoes, respectively, to a constant voltage for components such as smoke units, LED marker lights, and cabin lights. The CVU usually consists of a rectifier to convert AC to DC, a capacitor to “smooth” the DC, and a voltage regulator to maintain the output DC at a constant voltage, frequently six volts as required for Seuthe smoke units used by Samhongsa-manufactured locomotives (Sunset 3rd Rail and Williams locomotives).

    I have encountered three types of CVU’s:

    1. MTH Proto-Sound 2/3 versions that power maker light LED’s and incandescent cabin lights (see my blog on dead-rail conversion of a Proto-Sound 3.0 locomotive).
    2. Sunset 3rd Rail CVU’s that are usually mounted at the front of the boiler and power Seuthe smoke units and marker light LED’s.
    3. Williams CVU’s that are similar to Sunset 3rd Rail CVU’s, but do not control the headlamp, and instead use a separate Headlamp Direction Board.
    Figure 5a: Proto-Sound 3.o Constant Voltage Unit in a Sunset 3rd Rail Allegheny converted to dead-rail. “Switched Battery B-” is also ground.
    Figure 5b: Typical Sunset 3rd Rail Constant Voltage Unit with dead-rail modifications. See Figure 4a for details on how the CVU is connected to power.
    Figure 5c: Typical Williams Constant Voltage Unit with dead-rail modifications. See Figure 4a for more details.

    Important Constant Voltage Unit Control Options: In the figures and discussion above, the Constant Voltage Unit power supply was modified to connect to Switched Battery+ and Battery- (ground) from the tender. These connections will always turn on the devices supplied by the CVU (although the locomotive-mounted smoke switch will turn on/off the smoke unit) when the battery is switched on in the tender. To allow the receiver to actively control the CVU-connected devices, the Switched Battery+ input to the tender-to-locomotive connector can be replaced with a relay, controlled by the receiver, that turns on/off Battery+ to the CVU. See the Figure below for an example. This relay is mounted in the tender, not the locomotive!

    Figure 6: Tender relay control of Switched Battery+ supplied to the locomotive CVU. The relay is “normally-open”.

    In this example, a 215H-1CH-FC12VDC relay, with a 1N4002RLG protection diode in parallel across the input control (these parts are available from by cutting and pasting the above part #’s into their search), will connect/disconnect Switched Battery+ to the locomotive’s CVU according to whether the Airwire G3’s RM1-8 output is on (shorted) or off (open-circuit). Unpowered (i.e., RM1-8 is off), the relay is “normally open”, so no power reaches the CVU from the relay. When the relay activated (i.e,, when the RM1-8 is on), the relay closes to supply Switched Battery+ to the CVU. Setting up the on/off logic for the Airwire G3’s RM1-8 output by remote control is described here, recognizing there are slight differences between the device part numbers and wiring hook-up described in the link and those presented here. It’s kind of neat to hear the mechanical relay quietly click closed and open…

    Of course, there are numerous other techniques for implementing a high-amperage switch that is controlled by the receiver or DCC decoder. This particular example is called a “high-side” switch that connects/disconnects battery power to the device, as contrasted with a “low-side switch” where the device’s connection to ground is controlled by the switch.

    Locomotive to Tender Connector

    Tender Conversion

    Good news: tender conversion is usually much easier and less diverse than the modifications needed for dead-rail conversion of locomotives.

    Reverser Unit Removal

    Sadly, the sophisticated electronics contained in the tender must be removed almost totally, including the reverser unit. These electronics are not to be confused with a possible MTH PS-2 or PS-3 controller that you probably want to keep as described in another of my blogs.

    Reverser-sound electronics from a Sunset 3rd Rail UP Big Boy tender.

    As I have mentioned in other blogs, it’s a shame some of the electronics containing the sound data cannot be reused, but I have not discovered a way to do this. (I still have hope of someday figuring it out, so I have kept and labeled all of the electronics I have removed – you should, too.)

    I strongly urge you to take pictures of the tender assembly and its electronics before removal or modification of any components – you might be glad you did. Document everything with a picture – that’s what cell phone cameras are for!

    The board removal process first consists of carefully disconnecting any wiring to the boards (with pictures and/or notes!). Usually, plugs are provided for these connections, but occasionally, clipping off the wiring becomes necessary. I would suggest that you leave enough wire connected to the board to facilitate a new wiring connection just in case you re-use or sell the boards.

    Wire removal may entail plug removal and wire cutting.

    Some of the wiring such as to tender lights and connections to the locomotive need to be carefully preserved.

    After wire removal, then the boards can usually be separated from the tender by removing mounting screws or two-sided tape.

    Board removal for a Sunset 3rd Rail Cab Forward tender.
    Care must be taken to separate the battery from the double-sided tape and then remove the tape from the tender.

    Battery Addition

    As I have mentioned in other posts, I mount the batteries for O scale steam locomotives in the tender. For 14.8V operation, I use 4 LiPo cells in series (the so-called “4S1P” configuration). Regardless of how you ultimately arrange the individual 3.7V LiPo cells relative to each other, you can’t get around the fundamental size limitations imposed by a single LiPo cell on O scale: the cell’s length. Generally, O scale tenders are not wide enough or tall enough internally to provide sufficient clearance for even a single LiPo cell aligned along the width or height of the tender. So, this almost always means orienting the cells’ lengthwise in the tender in some fashion.

    Even knowing this constraint, fitting a 4S1P battery pack into the tender  sometimes requires a bit of ingenuity/trial-and-error. There are no hard-and-fast rules here, so I will provide a series of figures showing how I’ve “done it.”

    Some suggestions:

    • Use thin Velco tape to mount the battery to the tender frame, usually on the chassis and not the tender hull. I mount the “hooks” side of the Velco to the frame, and the “loops” side to the battery – I suppose this is an aesthetic choice, but I believe consistency is good: so my rule is all Velcro on the frame are “hooks”, and all things that are mounted use Velcro “loops”. See picture below for the kind of Velcro I use.
    Thin, industrial strength Velcro useful mounting items inside the tender and locomotive.
  • Use three position, ON-OFF-ON switches when connecting the battery “+” side (the battery “-” should be well-connected to “ground”, which should include the tender and locomotive frames):
    1. ON: power supply for all items on the tender and locomotive
    2. OFF: “neutral” that completely disconnects the battery to prevent slow discharge when not in use
    3. ON: recharging jack
    • Use high-quality switches and recharging jacks. Cheap ones available on Amazon are generally foreign-made junk. Spend two or three dollars apiece and purchase them from reputable electronics distributors such as Mouser and Digi-Key. I have been sorry when I used cheap hardware.
    Example battery, switch, and charging plug mounting where this is plenty of room. Note the shielded antenna connection from the chassis to the Airwire receiver mounted on the side of the tender hull. Velcro is used to attach various electrical components, including Wago connectors that supply Battery + and Battery – (ground) to other electrical components.

    An example (on a Sunset 3rd Rail Cab Forward) where the battery must be mounted to the tender hull since the battery pack is just slightly too wide for the tender hull opening without scrubbing.

     Antenna Mounting

    Placing an antenna and external electrical connections is never an ideal process: compromises must be made that try to minimize the impact on aesthetics and maximize RF reception and accessibility.

    While far from ideal, I frequently place the antenna in the dark reaches under the tender chassis. The RF engineers are going to jump all over me for doing so because there’s a lot of metal in a nearby plane parallel to the antenna axis – the location “works”, but reception range takes a hit. The figure below is a typical example of mounting for the antenna, electrical switch, and charging plug.

    Example (in a Cab Forward) of antenna, power switch, and charging plug location on the bottom of the tender. The fit is tight!

    Sometimes, when the tender has a coal load, the antenna can be hidden underneath a “coal cloth” on the top of the tender. This strategy sometimes improves reception when there is an opening beneath the coal load where the antenna can be placed. Frequently the original coal “load” is either mounted with screws (if you look carefully) or is easily pried off with the mounting board. See Figure below.

    Example of coal “load” removal on a KTM Big Boy. Underneath is a cavity that is suitable for mounting an antenna

    At the risk of offending some purists, sometimes an opening can be cut in the tender hull where the coal load goes to afford both better antenna placement and internal access to the electronics in the tender. The opening will be covered over by the coal cloth. See the figure below for an example of this strategy.

    Example (Sunset 3rd Rail Big Boy) of an opening cut in the tender hull to provide antenna placement and electronics access. Note the “coal cloth”, which is non-metallic, over the opening to provide low-loss RF reception.
    Top view of the flexible “coal cloth” placed over the opening cut in the tender hull for antenna placement and electronics access.
    The coal cloth in the previous figure has been removed to reveal the open-cavity antenna installation in a Williams UP Challenger. The antenna is connected to a Tam Valley DRS-1, Mark III, RF receiver that operates on Airwire Channel 16. The nearly half-wave antenna provides better range performance compared to tender undercarriage installations shown in this blog.

    Antennas themselves involve some compromise because they must be short to fit within the confines of our locomotive or tender or in the area about them. Very generally speaking, shorter antennas are less efficient than longer ones. Most dead-rail transmitter/receivers operate (in the US) in the band ranging from 902 MHz to 928 MHz, which is one of the so-called “ISM” (Industrial, Scientific, and Medical) bands that does not require strict licensing to use. This means that the wavelength in vacuum is about 33cm, which at even “quarter-wave” makes for an antenna of roughly 8.25 cm or about 3.2 in unless, for instance, you reduce the length by making the embedded antenna wire helical.

    Compact, high-quality, quarter-wave 915 MHz ISM antennas are manufactured by reputable vendors such as Linx Technologies in convenient right-angle form-factors with RP-SMA connectors (see Figure below) and are available at Mouser or Digi-Key. Again, my suggestion is not to purchase cheap antennas of unknown quality: when range performance is poor it will be very difficult to know what to blame. Just don’t worry about the antenna and buy quality: it’s only going to cost you seven to 11 dollars US.

    A Linx ANT-916-CW-RCS antenna. It’s about 2.1 inches long. This antenna uses a helical internal antenna wire to reduce its length.

    Receiver Addition

    Because this topic is not unique to 3-rail, please see this post for a discussion of Transmitter/Receiver Addition.

    Lighting Modifications

    Three-rail locomotives have a variety of means for providing two aspects of lighting: constant output with changes in track voltage, and whether to turn on or off with direction or independent of direction, especially since AC operation makes it more challenging to determine direction.

    We have already talked a bit about the role of constant voltage units (CVU’s) for lights in the locomotive, and tenders often have colored marker lights and almost always have a white tail light. These lights are usually supplied with AC power supplied by the rails, so almost all of the electrical “infrastructure” used to supply AC lighting power must be replaced for battery-powered DC operation.

    These lights are often older incandescent bulbs that are more power-hungry than LED’s. Since dead-rail conversion involves the use of DC battery power around 14.8V or so, LED’s with the proper form factor and protection resistor to replace these incandescent bulbs are easy to find for colored marker lights or the rear light. The figures below are an example of LED installation in marker lights and tail lights.

    Details of marker light and rear light LED installation. Note that there are two rear lights using the heavier wiring. UV curing “glue” is used to hold the wiring and LED’s in place. This type of glue provides reasonable holding ability but can be easily removed if necessary. It has the added benefit that it will not harden until UV light is applied, giving the user plenty of time to carefully position the wiring and glue.
    Sunset 3rd Rail Big Boy LED marker light and rear light conversion (there are two rear lights in this case). Note the use of “canopy glue” to hold the LED in place and provide a “window”. When the canopy glue cures, it will be transparent. The LED lead wires were later painted black to reduce their visibility.

    If the original marker or tail lights are LED’s, then retaining most the wiring supplying power is desirable. Obviously somewhere along the wiring to the LED’s must be cut to convert to battery-powered operation, but look carefully for the protection resistor in series with one of the power leads to the LED, and do NOT cut the wiring between this resistor and the LED. As a side note, if you connect power directly to an LED without a protection resistor in series with the LED: if the power supply “forward biases” the LED you will burn it out with too much current – a brief, tiny nova will ensue. Frequently, the protection resistor is near a plug, making it a convenience to retain this plug.

    For 14.8V operation, the LED’s I have used require protection resistors ranging from 470 ohms to 1.2 Kohm. The specific value is dependent on the LED: smaller LED’s generally tolerate smaller maximum currents, so larger protection resistances are required.

    LED’s produce light only if positive voltage is applied to its “anode” relative to its “cathode.” It’s the electrical equivalent of a stop-valve: current flows easily through a diode in only one direction, so even in the original wiring, LED’s anodes are supplied with either a positive DC or positive rectified AC voltage.

    Ensure that the original DC or rectified AC voltages are reasonably close to replacement battery voltage so that you do not need to modify the resistance of the protection resistor, and make sure that the replacement power is connected with the same polarity as the original power supplied to the LED. If powered “backwards” for very long, damage to the LED may result. Brief reverse biasing with the protection resistor in series with the LED to test for the proper polarity is not harmful, just don’t apply it for long. The 14.8V batteries I use are generally not vastly different from the original voltages supplied to the LED’s, so increasing the the protection resistance is usually not necessary.

    After connecting the LED to battery power, if the LED seems too bright, by all means add an additional resistor in series with the LED and the original resistor to reduce the current through the LED. A higher-than-necessary value for the total series resistance will do no harm, and oftentimes LED’s are just too darn bright using the “proper” value for the protection resistor.

    Electrical Modifications

    Mechanical Modifications

    Caution: This topic is somewhat controversial. Some may not like the suggestions under this topic. Please try to remember that the discussion is only offering possibilities, not hard-and-fast rules.

    The most important mechanical modifications to 3-rail locomotives deal with the “high-rail” flanges on all of the wheels. If you intend to use high-rail trackage, then the discussion below is probably irrelevant.

    However, if you, like me, dislike the very non-prototypical appearance of the high rail trackage and the large wheel flanges that go along with this kind of trackage, or if you want to operate on 2-rail track that conforms to the “Scale Track, Standard Scale” NMRA Standard S-3.2, then the high-rail flange profile requires modification to better match “Scale Wheels” in NMRA Standard S-4.2 and “Wheel Contour” NMRA Recommended Practice RP-25.

    There are no doubt numerous strategies for replacing the high-rail flanges, and I’m sure I haven’t thought of them all. The two approaches I will discuss are wheel replacement or flange profile modification.

    A final note of caution before describing details: Please determine how you will use your dead-rail locomotive. If you will be using the locomotive strictly on un-powered rails, as I do, then proper wheel insulation is not an issue.

    However, if you intend to run your locomotive on powered trackage, then proper wheel insulation may be required. If the powered trackage is 3-rail, then insulation is not an issue since the wheels are not insulated for operation. However, if the trackage is powered 2-rail, then proper wheel insulation is required. Operating originally 3-rail locomotives on powered 2-rail requires wheel insulation, which is a major hassle, especially when dealing with locomotive drivers.

    The powered 2-rail standard is that the locomotive frame is electrically-connected to the right rail, so all of the locomotive’s left wheels must be insulated; and the tender’s frame is electrically-connected to the left rail, so all of the tender’s right wheels must be insulated.

    My suggestion: don’t operate dead-rail O scale locomotives on powered trackage at all, but most notably not powered 2-rail trackage. But, this may not be an option for you, so you must address proper wheel insulation for powered 2-rail operation, and you must ensure the locomotive and tender frame do NOT share a common ground. Otherwise, a short across the two rails will occur.

    Wheel Replacement

    Wheel replacement may involve completely replacing the high-profile wheel with an RP-25 conformant wheel, or, in the case of steam locomotive drives, replacement of the outer rim or “tire.” We will discuss each in turn.

    Complete wheel replacement is a very feasible option for leading/trailing locomotive trucks and tender wheels. Specialty vendors such as Northwest Short Line (NWSL) and Precision Scale offer numerous sizes and styles of RP-25 compatible wheels and axles. I will warn you that navigation of these companies’ offerings is either fun or tedious, depending on your level of desperation and patience. While looking for what you need, remember that this is supposed to be a fun hobby.

    The knottiest problem with wheel replacement is dealing with the axles. You can either completely replace the wheel axles along with the wheel replacement, or you can bore out the replacement wheels’ inner diameter to match the original axle’s diameter.

    For instance, NWSL almost entirely offers both replacement wheels with an inner diameter of 1/8″ for O scale and axles that match this diameter. High-profile wheel axles are almost always a larger diameter. If you can find a 1/8″ axle that matches the length and end-style of the original axle, by all means go with this option.

    Unfortunately, you may not always find a suitable axle. If you are handy with a lathe, then making a new 1/8″ diameter axle that matches the original axle’s length and end-style will be a fun project. If machining is not your forte, then you might try boring out the replacement wheel to match the original axle’s diameter.

    I will warn you, however, that boring and mounting the replacement wheel on the original axle is somewhat challenging, and requires the right tools, technique, and skill.

    As a final note on wheel replacement, ensure that if you intend to operate your locomotive on powered 2-rail trackage (which I don’t recommend), then proper wheel insulation is required. The vendors above offer insulation options along with replacement wheels and axles.

    Flange Profile Modification

    The NMRA Recommended Practice RP-25 and NMRA Standard S-4.2 help define the wheel flange profile that will operate reliably on two-rail trackage meeting the NMRA Standard S-3.2. These wheel profile and trackage standards are more prototypical-looking than high-profile flanges and track, and RP-25 profile wheels will work on high-profile rail if it’s well laid, but high-profile wheels will no operate reliably on NMRA Standard S-3.2 compliant turn-outs.

    RP-25 compliant replacement steam locomotive drivers are generally not available, so modification of the original drivers is usually required.

    In some cases, it is possible to remove the driver center from the “tire.” Then an RP-25 compliant tire is machined and press-fit onto the driver center. Some modelers, such as Joe Foehrkolb and Glenn Guerra excel at this process, but I don’t, so my alternative is to machine the tire while still integrated with the center driver until its flange profile approximates the flange depth (approx 0.036″) and flange width (0.039″) dimensions of an RP-25 profile.

    The following photos demonstrate my process. Of note is that the most critical dimension to “get right” is the flange depth, which means reducing the flange diameter with a series of small “side-cuts” (parallel to the lathe spin axis) on a lathe until the flange diameter is about 0.072″ larger than the “tire” diameter. Then a series of small face-cuts (radial to the lathe spin axis) reduces the flange width until it is approximately 0.039″. However, this dimension is less critical than the flange diameter, so the flange width should not be reduced by so much that it leaves a sharp flange edge.

    Step 1: removal of the side-rods
    Step 2: removal of the driver axle coves
    Step 2: Sometimes you must use a specialized “wheel puller” to pull the drivers off the axle that is mounted inside a solid, bored chassis
    Step 3: Machining the drivers: The tail-stock holds the axle steady and square. A series of small side-cuts (parallel to the lathe spin axis) with a right-handed cutting tool decreases the flange diameter until it is approximately 0.072″ greater than the driver diameter to create a flange depth of approximately 0.036″. Then a series of small face-cuts (radial to the lathe spin axis) with a left-handed tool reduces the flange thickness to approximately 0.039″. This dimension is less critical than diameter reduction, so residual flange appearance is an important concern.
    Final driver: the flange depth is approximately 0.036″ and its width is approximately 0.039″.
    Example of high-profile flange reduction for both the drivers and truck wheels.

    General Battery Issues


    One of the most vexing challenges for me when doing dead-rail conversions on O scale steam locomotives is what battery to select. As nearly as I can determine, lithium polymer (LiPo, see LiPo Wikipedia) batteries are the almost-universal choice among dead-railers, so the choice of battery technology was not much in question for me, but the battery voltage and size is still a choice to be made. I’ll deal with each of these in turn.

    Battery Configurations

    I’m not sure how I fell into the 14.8V “camp” for LiPo batteries on O scale dead-rail conversions. Maybe it’s because CVP pushes them for their Airwire products (CVP Airwire). I think CVP has valid admonitions about using higher voltages in regards to radio control range performance and cooler operation (see for instance CVP G3 Decoder User Guide, page 12). And, and almost all of the O scale operating modes (2 rail DC, three rail AC, TMCC, DCS) seem to have 24V or so maximum operating voltage, which is getting close to damage threshold for some radio receivers such as the CVP Airwire receivers. So, would 11.1V (3 LiPi cells in series, “3S” as discussed later) work? Probably just fine in most cases. The plus for 14.8V LiPo is that a variety of battery physical and power configurations are offered at 14.8V, which I’ll address next.

    There is probably a good deal of lore and religion surrounding the specifics of which brand and configuration of LiPo battery to choose for dead-rail. I’m going to try to stick with what I have tried, not what might theoretically be “better” or “worse.”

    Let me start with the less controversial part of my decision process: configuration. LiPo batteries come in a large variety of sizes and configurations (see for instance this site), but in my personal experience with dead-rail, the LiPo’s seem to have an individual cell size roughly that of an AA cell with 3.7V output with a charge capacity of around 2000 to 2600 mAh. The individual cells are connected to achieve a total output voltage of about 14.8V (four connected in series, thus the term “4S”), but what varies is the total charge capacity and its ugly handmaiden – physical size.

    This is the bear: We want large charge capacity for longer running times, but we in O scale must fit the batteries in often-tight spaces (at least compared to G scale) such as tenders where we also put radio control receiver boards, sound cards, speakers, etc. Of course, HO scale has even more severe volume constraints, but with approximately one-sixth the mass the locomotives must pull.

    Personal experience here: I tried to fit an eight-cell (two rows of four vertically-stacked cells, 2.6″ x 2.8″ x 1.4″, 6000mAh, CVP BATT2) configuration into several O scale tenders, and that battery pack just flat-out would not fit. Even though this configuration was only one cell high, O scale tenders are just not tall enough to fit even one cell oriented vertically – the cells must lie sideways to fit. This cell-length limitation is important to remember for O scale. You might find space in diesel locomotives, but not steam locomotive tenders. These limitations were a big disappointment for me since I wanted to cram a large storage capacity battery pack in the tender and run “forever” (forever being at least four hours).

    Sigh… Backing off in size, I have found that 2x2x1 LiPo battery packs will fit in O scale tenders with the individual battery cells running along the length of the tender. See the Figure below (pardon the body parts). You can see that this configuration also comfortably fits the width limitations of O scale tenders, too.

    Figure 1: 2x2x1, 14.8V battery configuration that fits. For reference, the CVP G3X receiver board between the battery and speaker is approximately 4″ long.

    A note of caution: you cannot stack too much on top of this configuration before you lose vertical clearance inside the tender. For instance, I thought this was going to work:

    Figure 2: This didn’t fit!

    Stacking the receiver board on top of the battery would be a useful space-saving strategy, but this configuration would not clear vertically in all tenders I tried (Big Boys, Cab Forwards, Challengers, and Alleghenies). The receiver board manufacturers would probably dislike my mounting electronics on top of batteries, even with sufficient clearance.

    Battery suppliers

    My experience is confined to three battery suppliers of 2x2x1 LiPo battery packs: CVP, Tenergy, and “HJE.” All come with a Protection Circuit Module (PCM) that provides:

    • Overcharge, over-discharge protection
    • Overcurrent protection
    • Short-circuit protection
    • Voltage- and current-balance
    • Temperature protection


    Recent experience

    Example of a 1x2x2, 4S1P (4 Series, 1 Parallel) battery configuration (from on a dead-rail install of a PS3.0-equipped (w/ DCC operation) MTH Virginian Triplex. This battery configuration reduced the thickness sufficiently to fit alongside the PS3.0 board where the original PS2.0 battery pack was mounted. The PS3.0 replacement board was obtained from Ray’s Electric Trainworks.

    More creative 14.8V battery configurations are possible that include one battery-diameter thickness solutions such 1x2x2 ( with dimensions of 131 x 36 x 23mm (LxWxT), so it’s approximately one battery-diameter thickness, two battery-diameters wide, and two battery lengths long (~5.2″). See the picture above for an example of using this thin configuration in a very tight mounting configuration on an MTH Virginian Triplex with a PS-3.0 board operating in DCC mode. See this blog for more details.

    Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3


    Don’t jump to conclusions; the C&O 2-6-6-6 Allegheny with MTH Proto-Sound 2.0 (PS2.0) I found on eBay was NOT manufactured by MTH – it is a brass locomotive produced by Sunset 3rd Rail (Figure 1) and converted to PS2.0 (see MTH PS2.0 Upgrade Manual). See Figure 2. The original tender QSI-OEM Digital Soundboards, tender and locomotive wiring harnesses, and the Suethe smoke units and their voltage regulator board in the locomotive had been replaced.

    Figure 1: Sunset 3rd Rail C&O Allegheny box info

    Figure 2: Original tender Proto-Sound 2.0 electronics and harness wiring

    It was a well-done conversion, so I was very reluctant to tear out the tender PS2.0 control board, and the wiring harnesses in the tender and locomotive. The PS2.0 conversion used an MTH smoke unit that has both fan speed and smoke intensity controls.

    Figure 3: MTH Smoke Unit with funnel

    The CVP Airwire receiver boards I typically use for dead-rail conversion don’t have this level of smoke unit control. And, the PS2.0 board used a speed encoder on the locomotive motor’s flywheel to synchronize the PS2.0 board’s sound. See Figure 5 for the speed encoder reader and flywheel strip and 5b for additional electrical connections.

    Figure 4: Original Constant Voltage Unit wiring with dead-rail modifications indicated

    Figure 5: Speed encoder, flywheel strip, and electrical connections for the Constant Voltage Unit.

    Figure 5b: Locomotive harness wiring after modifications connecting the Constant Voltage Source to Battery +/- and replacing incandescent bulbs with LED’s

    All of these built-in features were pretty nice, but I still wanted a dead-rail conversion.

    Hmm… Looking around, I found out that Proto-Sound 3.0 (PS3.0) had DCC/DCS control options and the wiring harnesses are the same for PS2.0 and PS3.0 boards (see for instance MTH PS3.0 Upgrade Manual). Things are looking up. Then I found a great site, Ray’s Electric Trainworks, that provides PS3.0 replacement boards and great support.

    My thought was this: if I can upgrade the locomotive to PS3.0, then I can jumper the PS3.0 board to DCC operation, disconnect the original rail power/communication wiring, and re-connect the rail power/communication wiring to the DCC outputs of a CVP Airwire CONVRTR-60X receiver (CONVRTR Users Guide). Easy, right? Not so fast.

    Ray at Ray’s Electric Trainworks was a great help: he steered me to the right PS3.0 card that I needed for the tender, and he loaded the Allegheny sound file for me. Otherwise, I would have needed a bunch of DCS infrastructure to load the sound file. And, he gave me a rebate for the old PS2.0 card! Great guy.

    OK, I have the PS3.0 card from Ray. The PS3.0 card came mounted in its plastic carriage that is screwed on the tender chassis through pre-existing holes. The heatsink is oriented a bit differently between the PS2.0 and PS3.0 – no big deal – I just needed to drill a hole in the tender chassis in a slightly different place. The PS3.0 doesn’t use a Ni-MH battery, so out it went. That was a good thing, too, since I needed the real-estate for the replacement LiPO battery that would supply power to the control boards, lights, smoke unit, and the locomotive.

    Locomotive Modifications

    Here is a diagram of the locomotive wiring harness from the MTH PS3.0 Upgrade Manual with my annotations.

    Figure 6: Locomotive PS3.0 wiring harness with modifications indicated

    Since I wouldn’t be sending track power to the tender, I cut the Ground Lead and Pickup Roller Leads wires and re-purposed them by connecting these harness wires to the Constant Voltage Unit, which is a heat-shrink blob whose input leads were cut from their original chassis connections (see Figure 5 again).

    While I was at it, to reduce power consumption, I removed the incandescent cabin and headlight bulbs and replaced them with Yeloglo LED’s (see Yeloglo description) whose + input was in series with the Yeloglo’s 470-ohm resistor for 10-16 Volt operation. Yeloglo LED’s have an excellent yellowish output reminiscent of incandescent light.

    Tender Modifications

    The diagram below shows the tender wiring harness with my modifications.

    Figure 7: Tender PS3.0 wiring harness with modifications indicated

    Continuity testing revealed that the locomotive Roller Pickup Leads and the Ground Lead were connected to Pin 1 and 3 of the 7-pin connector, respectively.

    Note that BOTH locomotive and tender Ground Leads (both are black) that are input to the PS3.0 on pins 3 and 4 of the 7-pin connector, respectively, MUST BE DISCONNECTED FROM THE LOCO/TENDER FRAMES AND CONNECTED to the “B” DCC output of the CONVRTR. This pair of connections was the trick. I initially connected ONLY the Ground Lead coming from the locomotive (pin 3 of the 7-pin connector) to the CONVRTR, and it did NOT work! I don’t know if connecting only pin 4 of the 7-pin connector would work – I didn’t try it.

    Similarly, the red wire that is input to the PS3.0 on pin 1 of the 7-pin connector (which was originally connected to the locomotive Roller Pickup Leads) is disconnected from the plug bundle that connects the tender to the locomotive and is connected to the “A” output of the CONVRTR.

    The “harness side” of the two cut wires originally going to the Pickup Roller Leads (red) and Ground Lead (black) on the locomotive, were connected to switched Battery + and Battery – (ground), respectively, to provide power to the locomotive’s Constant Power Unit.

    Note: “Switched B+” means battery power coming from the Battery’s + terminal that is turned on or off with a switch (you want to be able to turn off the power!). “Battery – (ground)” means the connection to the Battery’s negative terminal that is usually grounded to the tender chassis by a battery charging plug.

    A picture is worth a thousand words, so studying Figures 6 and 7 will give you the story of what wiring cuts and re-connections that are needed to convert a Proto-Sound 3 steam locomotive to dead-rail.

    Other Dead-Rail Conversion Details

    Of course, there are other aspects to the dead-rail conversion that are required such as the addition of battery power and CONVRTR connections, and removal of center-rail pick-ups and electrical connections that are part of a typical 3-rail to dead-rail conversion for an O scale steam locomotive. These conversion aspects are discussed in another blog.


    In summary, if you have a locomotive with the PS3.0 installed, conversion to battery-powered DCC operation and radio control (dead-rail) is very simple once you know the few wiring cuts and re-connections you need to make. The DCC operations for this particular locomotive can be found in the MTH document “Premier 2-6-6-6 Allegheny Steam Engine .” What you preserve with the PS3.0 is good DCC functionality, the original sound, and coordinated smoke – and that’s a pretty nice combination.

    What is Dead-Rail?

    At its most basic, “dead-rail” is battery power and radio control of the model railroad locomotive. Some folks don’t like the “dead-rail” term and call it “battery-powered radio control” (BPRC). I understand and am somewhat sympathetic with the dislike, but for convenience and practicality (“dead-rail” is arguably more specific than “BPRC”), I will stick with the term “dead-rail.” Those two features – battery power and radio control – lured me in. Googling “dead-rail” will provide you with lots of excellent sites that explain “dead-rail” in detail, and they will provide you with additional resources. The starting site for me was, created by the Dead Rail Society of San Diego. They have the trademark on “Dead Rail” that they allow others to use freely (courtesy dictates that you let them know). This site packs a lot of useful information such as suppliers, how-to articles, videos, photos, and links. Go there and learn.

    Welcome to O Scale Dead Rail

    Welcome. There are more than a few excellent “dead-rail” sites around (the most notable is, but I have dedicated this blog to the application of dead-rail to O scale. Yep, it’s a narrow topic that came about in my search for information and guidance when I started converting beautiful brass O scale steam locomotives to battery power and radio control.

    I love O scale because it provides excellent detail (at least for my aging eyes!) at a reasonable size. I recently “got back into the hobby,” but I was daunted by two significant problems, the first of which is specific to O scale:

    1. 2-rail versus 3-rail: I hated that I would have to choose whether to be in the “2-rail” or “3-rail” camp. There are lots of beautiful locomotives available that operate in one or the other configuration. I wasn’t willing to choose between 2-rail and 3-rail just because of the way a locomotive receives power and communication, and either choice led to the second big problem: wiring.
    2. Wiring: I have visited some beautiful club layouts, and what struck me was the amount, complexity, and cost of installation for the delivery of power and control to locomotives. Since I had no investment in either 2-rail or 3-rail operation, I had the freedom to choose how to power and control locomotives.

    The solution to both of these problems for me was dead-rail. It might not be for you, but the recent advances in batteries and radio control, greatly fostered by the market strength of related hobbies, was the “dream come true” for powering and controlling O scale locomotives.

    But my choice to use dead-rail for O scale led to some challenges:

    1. Size: Believe it or not, my biggest hurdle adding dead-rail to O scale was finding and using space available for adding batteries, radio-control receivers, antennas, and DCC decoders (sound-only and general purpose). Many of the battery and radio-control receiver products were designed for Garden (G) scale since the G scale problems of outside use over long distances pretty naturally leads to a desire for battery power and radio control. G scale is fantastic for providing lots of space to add things like batteries, RC receivers, and antennas, but O scale offers considerably less volume and real estate than G scale for these dead-rail components.
    2. Existing features: At the least, O scale locomotives operate as either 2-rail or 3-rail, and both categories require slightly different dead-rail conversion strategies. Also, many of these locomotives have existing lighting, and smoke- and sound-generation features that need integration with dead-rail and radio control. Some O scale locomotives have DCC controllers, and fortunately, it’s not difficult to convert them to dead-rail operation.

    I learn best by specific examples, and that’s what I will be offering on this blog: my personal experience. I am relatively new to the hobby, and some of my inexperience will probably show. No doubt you the reader will have plenty to say about the topics I cover. Folks have lots of valuable and solid experience, insight, and opinions on this topic. I hope I don’t step on any toes, but my apologies ahead of time if I unintentionally do so. Thanks.

    Update 09 Oct 2019: I have become aware of a Facebook group O Gauge Battery Trains that might be of interest to O scale dead-railers.