Wiring a Digitrax PM42

HemiAdda2d Feb 23, 2007

  1. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    Anyone tackled one of these lately? Any pitfalls to watch out for? The manual is somewhat tricky to read. I am especially interested in how to interpret the manual as it applies to wiring up auto-reversing sections.
     
  2. okane

    okane TrainBoard Supporter

    1,923
    860
    43
    Mine I pick up today. Does not look that difficult.
     
  3. SD70BNSF

    SD70BNSF TrainBoard Supporter

    499
    0
    16
    Hemi,

    I've got two PM42s wired up as standard short circuit managers (not auto-reverse) and it was pretty straight forward. Looks like you simply bridge both the Letter and corresponding Number edge pins to make that section an auto-reverse. I've heard you shouldn't have a short circuit section feeding an auto-reverser on the same card. And lastly give each of the Boards a different ID number. In my case, I'm using JMRI (free computer software to control the whole layout). I have adopted the standard that no board will have ID #1, since this is the default for any new board added to the system, and JMRI has trouble addressing PM42s that are board ID 1.

    Hope that helps,
     
  4. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    Waitaminnit, you saying I shouldn't use the short-circuit protection as well as auto reverse on the same block on the same PM42? I'm lost... :confused:
     
  5. dstuard

    dstuard TrainBoard Member

    981
    1
    20
    Each section may be configured as a circuit breaker OR a reverser. Digitrax original documentation did describe using a breaker section followed by a reverser, but after some "variable" results, they no longer recommend it (no real reason given), and the associated figure is no longer in the documentation. AFAIK, many folks still use it that way though, but YMMV.

    If you have access to the Yahoo Digitrax group, check out PM42.pdf in the files area for an overview of the PM42.
     
  6. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    I don't have access to Yahoo at work... ;) I'll check into it at home.
     
  7. SD70BNSF

    SD70BNSF TrainBoard Supporter

    499
    0
    16
    Let me first state that I regard Doug as more of an expert in Digitrax DCC than I am. So if I conflict with him, pay me no attention, I'll learn from him.

    Theoretically you could configure one of the PM42 sections as a circuit breaker, then use the output of that section to feed a different section configured as an auto-reverser on the same PM42 card. In this scenario, you have used 2 sections of the 4 of a PM42, with one being the circuit breaker and one the auto-reverser. I believe, and Doug can correct me if I'm wrong, but you don't want to do that. You would use 2 seperate PM42s, one feeding the other, with the second PM42 card section being configured as the auto-reverser.

    In my case, I have elected to use Loy's Toys Automatic Reverse Section Controller for each of my reverse sections, I only use the PM42 as a Power district circuit breaker.
     
  8. okane

    okane TrainBoard Supporter

    1,923
    860
    43
    Hemi

    How many reverse loops did you finally end up having?
     
  9. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    I'm not sure. I have the staging return loop, the wye at Plain, and possibly the helix. I really do not want to buy more quipment (nor can I really afford to) to make this work. If I have 3 reversing sections, should I not us the remaining portion of the PM42 for a separate power district? I had hoped to power the visible mainline and helix with the booster, and the staging area with one of the PM42's sections. Will this not work now? :(

    Will one section of the PM42 used as a reverser not also control a double-gapped block?
     
  10. SD70BNSF

    SD70BNSF TrainBoard Supporter

    499
    0
    16
    You should be able to do that. Feed the output of the booster to each section of the PM42. Configure 3 of the sections as the Auto-Reversers, and the 4th section as circuit breaker. Then wire to the layout. You would double gap between the staging area, and the rest of the layout. The fourth section would feed the staging area. The 3 others would go to a double gapped reverse section of their own.

    In operation what will happen is that if you short the layout in any of the areas other than the staging area, the entire layout will come to a halt including any running locos in staging. If you short out the staging area of the layout, only staging will halt. When you short the booster, the everything fed from the booster will halt.

    In the future you could add a second PM42 to handle subdividing the layout into power districts. Then a short in a power district will only affect that district.

    I hope that was clear (or at least clearer than the Mississippi, and trust me I live only a mile by crow from the river, it ain't clear).
     
  11. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    OK, the reversing would work, but if I short it, the whole layout basically goes down, unless it is in staging (and I can live with that; this is a small/mid-sized layout, not a club-sized monster). In the future, it seems I could wire the reversing sections as their own power district, using another PM42. Do I have this right?
     
  12. SD70BNSF

    SD70BNSF TrainBoard Supporter

    499
    0
    16
    Yep, I believe you do.

    But don't think that the reversing sections have to be in their own power district. Decide on a whole layout level where you want power districts. Think in terms of, if I short the layout in this area, what do I want to keep running, and what do I shut down.

    For instance, you might divide your layout into staging, mainline, helix, and other yards, etc.
     
  13. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    I think I'll have 2 districts: staging, and the rest of the layout. Chances of running a turnout in staging are much higher than on the mainline. That will leave me a separate section of the PM42 open, in case I run into another reversing section, or a new district. The PM42 then will be only for auto-reversing...
     
  14. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    22,014
    27,407
    253
    I wired one section up yesterday, after thoroughly reading and digesting the manual. The schematic drawings a page or 2 past the actual 44-pin diagram really simplified it. For the first time ever, a train (D&RGW 5507 and a SOU autorack) ran from one end of staging, thru the loop, and back; seamlessly, without the old 0-5-0 coming to the rescue!

    Thanks, everyone, this was much easier than I had imagined!
     

Share This Page