I thought I’d switch things up a bit. I’ve only shared dead-rail conversion posts for steam locomotives so far, but I figured showcasing the conversion of an O Scale diesel locomotive would be worthwhile. After all, not all readers share the same affinity for steam locomotives as I do! Converting a diesel presents a few unique challenges compared to steam locomotives, which makes it all the more interesting.
I was searching for a 2-Rail MTH diesel locomotive that didn’t require wheel and coupler conversion and provided a PS-3 for DCC dead-rail operation. Fortunately, I found what I was looking for on eBay – the MTH Premier Norfolk and Southern SD60E Diesel (MTH 22-20596-2) at a reasonable price, which ticked all the boxes. This choice allowed me to focus on a more straightforward dead-rail conversion, emphasizing incorporating battery power and a small but powerful (13A) ProMiniAir Receiver, with minimal modifications required. I opted for MTH because of its rich, DCC-accessible features, including lighting, sound, and smoke, and its maintenance-friendly design, making it relatively easy to open up.
I had to open up the locomotive and look inside to develop my dead-rail conversion plan. While MTH provides exploded drawings of some locomotives on their parts site, unfortunately, they are not yet available for the MTH 22-20596-2 model.
Notwithstanding the lack of good diagrams, removing the upper plastic shell was easy; remove eight screws and the rear coupler, and you’re in!
Separating the chassis from the upper shell, we’re confronted with a very crowded interior (see photos below)!
The interior space is narrow and jam-packed with two motors, a PS-3 board, switches, lights, and wiring.
Two conveniently-located switches are shown below.
Based on this examination, I made the following observations:
- I could not figure out how to place a battery in this space. Even flat batteries (0.2 to 0.3″ thick) would not fit!
- The 2-Rail/3-Rail switch could be repurposed as a 2-Rail/Dead-Rail switch, making it feasible to maintain 2-Rail DCC operation and add DCC Dead-Rail.
- The DCS/DCC switch could be repurposed as a Battery Power ON/CHARGE switch.
- Later on, I will demonstrate that it is possible to fit the Receiver and Amplifier of the ProMiniAir inside the shell.
To combine power and control of the locomotive, I had the option to set up the ProMiniAir Receiver in the trailing car along with the battery and send track-level DCC from the ProMiniAir Receiver to the locomotive instead of DC power. But for this post, I placed the ProMiniAir Receiver inside the locomotive and connected it to battery power from a trailing “battery car,” creating a straightforward battery-powered setup.
I will show in a future post how to locate the ProMiniAir Receiver/Amplifier in the “battery car” and supply the locomotive with the DCC output of the ProMiniAir Receiver’s amplifier.
Based on these observations, let’s get into the dead-rail conversion details.
To allow track-based “2-Rail” or “Dead-Rail” Operation, we need to figure out how to get DCC from either the track (“2-Rail Operation”) or from the output of the ProMiniAir Receiver’s Amplifier (“Dead-Rail Operation”). The original 2-Rail/3-Rail switch that routes track power/signal to the PS-3 is shown below.
These connections were verified by using a multimeter’s resistance-measuring capability. Let’s see how this switch is designed:
When the switch is in the 2-Rail position:
- The Right Wheels’ output is directed to the PS-3’s DCC Track Right by shorting the “Track Right” end post to the “Track Right” center post.
- The Left Wheels’ output is directed to the PS-3’s DCC Track Left since it’s directly soldered to the “Track Left” center post.
When the switch is in the 3-Rail position:
- The Center Rollers’ output is directed to the PS-3’s DCC Track Right by shorting the “Track Left” end post to the “Track Left” center post.
- Both the Left and Right Wheels’ output is directed to the PS-3’s DCC Track Left by shorting the “Track Left” end post to the “Track Left” center post and the “Track Left” end post’s jumper to the “Track Right” end post on the opposite side of the switch. This connection shorts the Right Wheel’s output to the Left Wheel’s output on the center post that then goes to the PS-3’s Track Left!
The photo below shows how to rewire this 2-Rail/Dead-Rail Operation switch.
Repurposing this switch has the following features:
- The output from the center rollers is disconnected and closed off. Its role was only for 3-Rail Operation.
- The Right and Left Wheels’ outputs are located on separate posts at one end of the switch (for 2-Rail Operation).
- The Track Right/Track Left DCC outputs from the ProMiniAir Amplifier are located on separate posts at the other end of the switch (for Dead-Rail Operation).
Look at the DCS/DCC switch (see the photo below).
The two black wires are NOT shorted together for the DCC switch setting, sending logic to the PS-3 that it should operate in DCC mode. Conversely, if the switch is set to DCS, the two wires ARE shorted together, sending logic to the PS-3 that it should operate in DCS mode. So, all we need to do to ensure permanent DCC operation for either 2-Rail or Dead-Rail operation is disconnect the switch’s two black wires and close them off so they can’t short to each other or anything else.
We can repurpose this switch to provide battery power to the ProMiniAir Receiver/Amp or enable the battery to charge through an onboard barrel plug. The CHARGE switch setting is reserved for future expansion and has not been implemented. The battery Ground is directly connected to the Power “-” of the ProMiniAir Receiver/Amplifier.
After repurposing the switches, they were reinstalled, as shown below.
With the switches reinstalled, we focus on mounting the ProMiniAir Receiver and Amplifier in a location that avoids mechanical interference with installed components.
Since the locomotive shell is plastic, the antenna can be internally mounted. To reduce the mechanical interference from an 82 mm whip antenna, I replaced it with a Molex 211140 “surface-mount” antenna (found at Mouser or DigiKey) mounted in the cabin area.
After a bit of trial and error, the mounting locations of the ProMiniAir Receiver and its “tethered” Amplifier are shown in the photo below. The tethered design provides improved flexibility for mounting in crowded conditions.
Routing of battery power and Dead-Rail DCC signal wiring to prevent interference with closing up the shell is always challenging. My solution is shown below.
Note the battery power wires “snaked” out between the bottom of the chassis and the rear truck, which connect to the “battery car” shown in the next photo.
The “battery car” I used had a metal shell that did NOT have a removable top or bottom, so I was forced to fit a battery through the small door opening in the side of the car. Fortunately, I had an oddly-shaped battery from MTO (see here) that often fits in tight quarters where other 14.7V battery packs will not. This is a very valuable, if expensive ($80), battery configuration to have on hand for dead-rail installations.
The photo below shows the battery installed in the “battery car.” The battery power wires were passed through a small hole I drilled in the bottom of the car near the coupler. Because the battery is asymmetrically-shaped, its uneven weight distribution is counterbalanced by a steel weight strategically placed at the other end of the car.
The first demo shows we retained the standard track-powered, 2-Rail DCC Operation. The 2-Rail/Dead-Rail switch is set to 2-Rail to route the track’s DCC to the PS-3. The Battery power switch is set to CHARGE (OFF) to prevent draining the battery by powering the onboard ProMiniAir Receiver that is not providing DCC to the PS-3.
The video below is a demonstration of the Dead-Rail Operation in action. Battery power is provided by setting the Battery Power switch ON, and Dead-Rail DCC is sent to the PS-3 board by setting the 2-Rail/Dead-Rail switch to Dead-Rail. A Standalone ProMiniAir Transmitter (see this page for a detailed description) integrated with a WiFi-equipped EX-CommandStation provides a WiFi connection to an iPhone’s WiThrottle app. The commands from the WiThrottle app are converted to DCC by the WiFi-equipped EX-CommandStation. Then the ProMiniAir Transmitter connected to the EX-CommandStation transmits this DCC to the ProMiniAir Receiver onboard the locomotive.
The most challenging part of the installation was finding a location inside the locomotive for the ProMiniAir Transmitter and its Amplifier that did not mechanically interfere with the rich set of installed components. Also, routing the added battery power and Dead-Rail DCC signal wiring was challenging. Physical examination is essential for developing a dead-rail conversion strategy, but some trial and error was required in the end!
In a future post, I will show how to mount the battery and the ProMiniAir Transmitter/Amp inside the “battery car” and simply output full-power DCC from the ProMiniAir Receiver/Amp to the locomotive, eliminating the hassle of finding locations for the Receiver and its attendant battery power wiring inside the locomotive. This configuration is much like what I do with steam locomotives: install the battery and ProMiniAir Receiver/Amp in the tender and then provide high-power DCC to the decoder inside the locomotive.
One intriguing possibility is that this option can provide high-power DCC to two or more locomotives simultaneously. This is because DCC inherently sends commands to multiple locomotives, and the 13A Cytron amplifier has enough power to handle multiple locomotives.