How do I feed plain DC to loco from DCC track

Discussion in 'DCC & Electronics' started by Ott Gangl, Apr 1, 2008.

  1. Ott Gangl

    Ott Gangl New Member

    I have a specialty locomotive that will run only on pure DC. I am running Digitrax DCC on my rails. Will a bridge rectifier convert it without interfering with running DCC at the same time?

    Any help is appreciated. ....Ott
  2. nachoman

    nachoman Guest

    Most DCC systems can operate one locomotive on standard DC. I have heard, that a standard DC locomotive used in this fashion will be somewhat noisier.

    I am not sure what you are talking about by putting in a bridge rectifier. Are you talking about inside the locomotive? Keep in mind that if you put a bridge rectifier in a locomotive, you can no lnoger change the polarity to the motor, and the loco will run in one direction only :)

  3. Ott Gangl

    Ott Gangl New Member

    Thanks Kevin. I am talking about running a Crest radio controlled locomotive. Crest is a division of Polk Modelcraft Hobbies, Inc.

    I have some longer tunnels not easy accessible for track cleaning that often stall my locomotives while I try track cleaning. So I bought this system thinking since it doesn't depend on the track signal I could run a track cleaning operation with that locomotive. It needs pure DC to run correctly.

    Right now it is running on 3 cell Lipo 300 maH batteries, maybe I should just keep that setup, but I just wanted to try to see if track power could be kept even with a signal loss.

  4. steamhead

    steamhead Active Member

    Hi...I don't see why a DCC loco would stall where a DC would not. Dirty track will affect them both as long as power is picked up through the wheels....I know DCC is a bit finicky, but if the track is so dirty that it stalls a DCC, there's no guarantee that a DC would keep running.
  5. Ott Gangl

    Ott Gangl New Member

    Well, I'll just stay with the batteries, they work well enough, it was just a thought. Since I didn't get an answer if the DCC power on the rails can be rectified into pure DC it is moot anyhow...thanks for trying, I'll give Digitrax a holler and see what they have to say.

  6. steamhead

    steamhead Active Member

    You could hook up a regular DC pack to the track as well. Just use a DPDT switch and wire your DCC on one end, the DC to the other end, and your output from the center terminals. That way you get both...
  7. woodone

    woodone Member

    This is a good idea- steamhead. :thumb: I do not like the idea of the DPDT switch,:eek: too easy to forget what system your are running and what locomotives you have on the track. Either systems don't like one an other.
    I just use a plug into the layout - then the DCC system plugs into that plug, need to use DC. you must remove the DCC plug before you can plug the DC system in. That way there is only one system or the other that can power up the layout.
  8. steamhead

    steamhead Active Member

    Woodone...I like the plug idea. I have been contemplating using a plug, but for a different purpose. I have a D'trax Zephyr which can use standard DC packs as auxiliary throttles ("jump" throttles they call them..). You can use two of these jump throttles. What I've bee thinking of doing is using my older DC packs as "walk-around" throttles, but there's the problem of the power cord...I had thought it might be a good idea to get a 4-"pole" plug - 2 would be to feed power to the throttle, and 2 for the output. Is there such a beast..?? I know I could use 2 regular for each function, but I would prefer the single plug option...if possible.
  9. woodone

    woodone Member


    I am not sure what your are trying to do.:confused:
    Could you draw up a wiring schematic, so I could understand what your are trying to do?
    There all types of plugs and the likes out there, so what you want just might be a call away.
  10. cidchase

    cidchase Active Member

    I think yes :thumb:
  11. pgandw

    pgandw Active Member


    The general answer is the DC rectifier will not work. The issue is that DCC has a 15 volt (actual voltage varies from system to system) square wave signal on the rail at all times. While the full wave rectifier will turn the signal into DC, and drop the voltage by 1.5 volts, you are still left with full voltage DC on the rails with no way to control it.

    The rectifier will in no way interfere with the operation of DCC. DCC decoders have a full wave rectifier at the front end of the motor power circuit, too.

    Now if your locomotive has a radio receiver that will modulate the DC rail voltage from signals from the transmitter, then it can work with full DCC voltage on the rails continuously. But in this case, you basically have the equivalent of a DCC decoder installed - it just responds to a particular radio transmitter instead of a DCC system.

    The other possibility is to use the rectified DCC signal to recharge your batteries through an appropriate voltage and charge regulator.

    hope this helps
  12. doctorwayne

    doctorwayne Active Member

    I got some 5-pole plugs at Radio Shack several years back for my walk-around throttles. The fifth prong just ensures that it plugs in so that all polarities are correct. I thought that I had a photo, but I can't find it. The same plugs may not be available, anyway, but any electronic supply place should have all sorts of small, multi-prong connectors. You could also use 'phone cord with jacks, which is what the walk-around throttle for my MRC ControlMaster 20 uses.

  13. MasonJar

    MasonJar It's not rocket surgery

    Whatever plug/wire combination you use will have to be rated for 120V, since two of the four wires are delivering power TO the powerpack (i.e. basically an extension cord).

    I would think either about building/acquiring real DC handheld walkaround throttles (still used as "jump throttles" with the Zephyr), or going to something like the Digitrax UT-4, which is the basic "accessory" throttle, reasonably priced.

  14. Ott Gangl

    Ott Gangl New Member

    The DC to DCC plugs on my layout.

    Thanks for all the suggestions, I need to explain. Before DCC, when my layout ran on block control DC with four walk around plugged throttles, color coded, and separate dedicated throttles for my big yard, logging operation, seaport and engine operations like the round house and storage tracks, etc.,

    Each throttle had a common ground but the output end was just a 1/4 inch phono plug (see picture) which now are not connected. The knotted grey wire has lugs that connect all blocks together for DCC, the flat head plug, second down on left which comes out of the yellow hole and is now plugged into Cab1 comes from the Digitrax output.

    All it takes to convert any section, like the the yard, say, is to unplug the DCC plug (gray) and plug in a DC throttle, say white, and that section is now controlled by DC while the others stay DCC.

    By unplugging the main DCC plug and connecting the DC throttle the whole layout is now controlled from that throttle since all blocks are connected by the gray knotted wires with plugs that could be disconnected by just pulling the plugs. The phono plugs are just a single wire even if it is a stereo plug, I just used what was at hand.

    This system was put in because I put in a home brew computer block advance system that, when a route was selected to go from point A to point B, the computer would give the power to that cab one block ahead and drop the the power of the previous block as soon as the caboose was out of it and give that block to another cab if it was requested. It worked great and I didn't regret drilling 10,000 holes into 164 home etched PC boards and mounting the components.

    Then I had a lightning strike that did a lot of damage to all electronics in the house and also wiped out the route program stored in an EPROM.

    DCC had come along and I decided to go with DIGITRAX, a good decision, IMO.

    Why I even brought up this discussion is that I wanted to have a rescue locomotive when a train gets stuck deep in one of my tunnels. The radio controlled loco can go in and nudge the train past the bad contact spot while DCC is still on the rails and it would resume it journey. For that to happen I wanted a locomotive independent of track power and with my battery controlled one now it is fine.

    I have a three way slide switch on the locomotive that connects the power either from the battery or from the rail, but in order to run it from rail power DCC I need to rectify it into pure DC. So for rescue missions it would run on battery and for other train running it could use the rectified DC form the DCC rails.

    I apologize for the length of the post but I wanted to clarify my situation, thanks for reading.


  15. kmackenz

    kmackenz New Member

    work for DC to start...

    WOuld this same model work if I am planning a small layout say 11x7. WOndering if I can setup to start dc, I have the blcoks and controllers already. But do all the wiring so once further along I could switch to DCC. Just "switch over"....

    Looking to spread the spending on a startup railroad if you know what I mean...

    Any thoughts? Hope this is the right thread.
  16. MasonJar

    MasonJar It's not rocket surgery


    You are only going to "save" if you already have the DC stuff available. And you're not really saving, you're only delaying payment...! ;)

    However, yes it is realtively easy to switch from DC block control to DCC. You simply substitute the DCC system for one of your cabs. You will have to make alternate arrangements for any reversing sections you have (loops, wyes, turntables) as DCC handles them differently. But other than that, it is pretty straightforward.

  17. kmackenz

    kmackenz New Member


    I do already have the DC stuff!!!:thumb: Right, putting off the spending...

    So if I find a good reference for wiring for DCC I just place blocks into the setup as well? To get to get the DC to work. Then the blocks will also support the DCC as well. Still looking for a good wiring guide for DCC, be nice to find one for "converting" as well from DC... Coming into this new it seems a little overwhelming! :confused:
  18. Jim Krause

    Jim Krause Active Member

    What is the total output voltage of your three batteries? Will the motor in your "special" locomotive handle a 12 DC power supply? Just a couple of questions to ponder.
  19. Ott Gangl

    Ott Gangl New Member

    Jim, I just use one battery at a time, the battery are LiPoli (lithium polymer) 3-cell at 11.1 volt and 300 milliamp, more than ample to drive the radio receiver and the Sagami can motor in the locomotive.

    The specs on the radio control specify a 12-14 volt DC source. The motor never gets more voltage than the RC speed control allows at any speed setting on the RC transmitter, so there is no worry.


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