Older Mantua DCC Conversion


Railrunner130

Railrunner130

Well-Known Member
I have a bunch of older Mantua steam locomotives in HO-scale that I'd like to convert to DCC. The problem I am running into is that the locomotive gains electrical power on one side and supplies it directly to the motor while the other side gets power from the tender and supplies it via a wire to the motor. Is there a way to convert these locomotives?

Perhaps I would need to simply connect the body to the decoder using the appropriate wire and the power from the opposite side would be connected as per normal? Or would this fry the decoder or perhaps the motor? But then what would I do with the decoder output to the motor for that side?

I almost had one figured out. It had brass U-channels holding the main wheels in place which could have been replaced with plastic. The tender axles could have provided power from both sides, but then I realized that with the metal body there is no way to isolate it.
 
These are actually an easy conversion. First thing is to break the connection to the brush that gets its power from the locomotive's frame. It maybe a metal strap, wire etc, attached to the brush. It could be something as simple as the spring holding tension on the brush. You do not need to isolate the entire motor from the frame, just the brushes. One side IIRC, has a piece of insulation on one side of the brush spring, isolating that side. Just put another piece of insulation on the uninsulated side. I did it by stripping the insulation from another piece of wire, that is of similar size to the spring. Once applied, the brushes are isolated, and that is all you need. Other way to do this would be to replace the motor with a new can motor. Best way to determine if you need a can motor or not is to do a stall test with a VOM meter, hooked up to measure the amps the motor draws. If the stall amps are higher than the rating on the decoder, you'll need to replace the motor, or the motor magnet with those new rare earth magnets. The magnets will lower the amps the motor will draw and can make it run smoother, and even quieter.

The next decision will be, where to put the decoder. In some locomotives, there is room in the top of the boiler for a non-sound, 2 function decoder. Why a 2 function decoder? For a steamer, you really don't need more than 2. One for the headlight, and the other for the motor.

Then, after you decide where to put the decoder, the only thing left to do, is wire the decoder in. If mounted in the boiler, the installation is really easy. If in the tender, I would recommend at least a 4 plug mini connector, between the loco and tender. Although these locos weren't really designed to come apart, the plugs make that easier. The connectors are marked with a white dot on one side, and as long as the connector is plugged in with the white dots on the same side, the polarity will stay the same. If you want lights, it will require another 2 prong connector. The connections will be, Red wire, to the loco's frame. Black wire to the tender's frame. The Orange and Grey wires goes to to motor brushes. Make sure that these last two wire are soldered to the brush holders and not the spring holding the brush in place I always soldered these wires about halfway down the holders, just above the brushes themselves.

Now you can test the hookup, and program the decoder as you wish. The headlight wires can then be hooked up through the 2 prong plugs, the same way as the 4 prong plug.

This is the same way that I install DCC into brass steamers, and I've never had a problem, (electrical) with this system.
 
P1000242.png


Here is the locomotive in question.

From what I can gather from Carey, I need to put a piece of heat shrink on the spring loaded wire leading to the right electrical contact. Then, I'll need to solder the orange or grey wire right to that contact.

Is this correct?

I plan on installing a Digitrax DZ126T, so as long as I can find a good spot for it, I should be good. Is overheating a real problem, or is it perceived?

Thanks again guys!
 
Yes, that's right. Other people are going to have to give their experience with overheating, but the DZ126 is very small and should have a lot of air around it, so it might not be an issue.
 
Your problem here is how much amperage that old open frame motor will draw. You should probably test that. It isn't too hard to toast an N or Z decoder with excessive amp draw.
 
I'll look into the amperage part soon.

I took a good look at it and plan on getting the right hand lead (red) from attaching the wire right to the screw you see on the right.

The next item to ponder deals with the headlight. Half of it's power is provided by the lead weight it sits in, which is connected to the frame via screw. I'm thinking I need to isolate it and run a second wire (it is connected to one already) to the decoder. The alternative would be to replace the light with a well insulated and wired LED. Part B of this thought is - do I need to add resistors to LEDs that are connected to the decoder?
 
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