Minor DCC problem

Discussion in 'HO Scale Model Trains' started by jeffrey-wimberl, Mar 13, 2008.

  1. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    Recently I fitted an Athearn BB F7 A-B set with Digitrax decoders (DZ125's). They work fine most of the time but sometimes the lead unit won't start up on DCC (usually when the DCC unit is turned on for the first time of the day). If I switch the block to DC and give the locos enough power to just move them then shut down and switch the block back to DCC it then will start up and run just fine. Am I correct in assuming that this is because the decoder is having trouble determining whether or not the current it's getting is DC or DCC? I'm using a Bachmann DCC system so changing CV's is out at this time. Is there another way I can correct this or do I continue with the method I've been using? Starting the units separately isn't possible as the two units are hardwired together so they pick up power like a single sixteen wheel unit.
  2. Spawn of Chaos

    Spawn of Chaos Member

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    Just re-enter the loco's address on your DCC command station.

    I find that my locos often get "forgotten" and I have to re-select them even if their number is still on the screen. And this is with a Zephyr!
  3. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    Nope, doesn't work. If the solution was that simple I wouldn't have to ask for one. I'm thinking it's the decoder not being able to tell DC from DCC until it actually gets some DC.
  4. Trainiac77

    Trainiac77 Member

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    I wonder if the problem is in the motor itself. Perhaps the impedance goes below 10 ohms and when DC is applied it just so happens that the motor is stopped in another spot that has a higher impedance allowing the decoder to restart in DCC mode? Just a thought.
  5. MasonJar

    MasonJar It's not rocket surgery

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    My initial thought is to turn off the DC option, but you may not be able to this with the Bachmann DCC unit. Maybe ask your LHS to do it?

    But then I wondered if the units are hardwired together, how are you using (what sounds like) two decoders? Is it possible that there's some sort of interference between the tow if they are using common pick-ups for power and feeds to the motor(s)?

    Andrew
  6. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    That's an interesting point that I hadn't considered. I'll have to check into it. Thanks.
  7. Spawn of Chaos

    Spawn of Chaos Member

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    If you're using two decoders, but hardwiring them as one, that is probably your problem. Use "basic consisting;" that is, give the two decoders the same address. That way, though you won't have quite as good pickup for each one, you won't have the problem with the DCC detection anymore.
  8. nachoman

    nachoman Guest

    Why are you hardwiring locos together? As a kid, i had some LL cheapo F-7s that I hardwired together. They were pancake motors with 4 wheel pickup, and hardwiring them back to back greatly improved their performance. But I was also running on brass track! I would think the advantages of hard wiring locos with 8-wheel pickup on N-S rail would be small.

    Another thought - I am not a DCC guy yet, but, do athearn BB's with the steel wheels give any decoder issues, because they spark so much?

    Kevin
  9. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    The locos are hard-wired together, not the decoders. They're wired as if the two locos were independent unit and they are both programmed with the same address and the Bachmann system doesn't have 'basic consisting'. You just program two locos with the same address and off they go. I tried running the locos as individual units but nothing changed. I still got the same initial startup problem, mostly with the A unit (about 3 to 1).

    I wired them together because I use insul-frog turnouts. When the locos went over them as individual units the headlight would flicker. When the locos pick-ups are all wired together it's like a sixteen wheel unit picking up power, and guess what? No headlight flicker.

    I haven't observed any DCC issues with steel wheels. These two F units have nickel-silver wheels but another DCC F unit I have has the old steel wheels as does my PA2. I haven't had any problem with them.
  10. MasonJar

    MasonJar It's not rocket surgery

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    So the locos are hardwired (i.e. permanently) wired together to achieve 16 wheel (or whatever) pick-up. But this arrangement then only calls for one decoder. The decoder must be able to handle the draw from two motors, but should work fine.

    Either that, or you should wire them as separate units, use a decoder in each, and then "consist" them together with whatever method Bachmann DCC supports.

    Andrew
  11. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    Again, I will emphasize, they BOTH have their own decoders. I've tried running them as separate units, even with different addresses, the same problem popped up. Bachmann's method for consisting is to give each loco the same address and run them on one address. My locos are wired so that the pick-ups are wired together, so they pick up power like one sixteen wheel unit. the pick-ups are wired to the decoders in each loco, just as they would in a single loco. The decoder in loco A gets power from the shared pick-up and sends it to the motor in loco A. The decoder in loco B picks up power from the shared pick-up and sends it to the motor in loco B. Both decoders have the same address and therefore run on one address. For some reason the decoder in loco A has some trouble telling the difference between DC and DCC, sometimes it happens to loco B. It doesn't matter whether the locos are wired together or not. It still happens. Can I make it any simpler?
    :)
  12. wjstix

    wjstix Member

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    I was thinking maybe, since a decoder takes AC power from the track and converts it to DC to run the motor, maybe some of the DC from one unit was leaking into the incoming wiring of the other unit, causing it to think it should be running under DC. But if you've tried them as two separate units (i.e. with NO wiring connecting the two engines) and they're still doing it, that would seem to eliminate that as a problem.
    :confused:
    BTW - If you really need better electrical pickup, I would add wipers to add more pickup, and keep each engine and decoder separate.
  13. Spawn of Chaos

    Spawn of Chaos Member

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    Basic consisting is giving the decoders the same address. Advanced consisting is where you use decoders with different addresses.
  14. nachoman

    nachoman Guest

    I think i get ya. From a circuit standpoint, this should be no different than two locos picking up current from the same track. In other words, each motor is being controlled by a separate decoder, but draw from the same current source. Think about it - this is no different than two separate locos drawing current from the same power source-the track. The only difference you have, is that the pickups for both locos are wired together - much the same as the pickups for both trucks in the same loco are wired the same. It's not like each decoder is trying to run two motors, or like each motor is being controlled by two decoders.

    After I thought about how you have it arranged, my thoughts are that you have decoders that are somehow incompatible with your DCC system, or decoders taht are malfunctioning. Do you have the same kind of decoder in any other loco?

    Kevin
  15. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    No. These are the first DZ125's I've gotten. I have a DZ123 in a P2K PA1 and it doesn't do what these are. I'm pretty well convinced that what's happening here is a CV29 issue and if I set DC operation to OFF that should solve the problem. I just have to get the locos to a modeler who has a system that reads back CV's. I know one who close by but he's out of state at the moment.
  16. wjstix

    wjstix Member

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    Keep in mind DZ's are Z-scale decoders designed for low-volt/amp Z scale motors, whereas Athearn motors (assuming these are BlueBox ones) have pretty high amp draw, so those decoders aren't really a good choice for those locomotives.

    I edited my earlier post, so maybe you didn't read it, but did you try running the two engines with NO wiring connecting them?? Since a decoder draws AC from the track and converts it to DC to run the motor, maybe some of the DC output of one decoder is getting into the AC input of the other decoder, making that decoder detect the DC and switch over to DC.
  17. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    The DZ125 is designed for a 2 amp peak load and constant 1 amp motor load making them robust enough for use in most HO equipment, in fact Digitrax suggests they be used in HO applications. These two loco are equipped with the newest 5-pole skew wound motors and draw very little power. The gears have also been cleaned of any flash and have had the 'pearl drops toothpaste' treatment to smooth the teeth. The two of them together draw .75 amps at full stall load meaning each loco draws about .37 amps at the most. I thought something was wrong with my meter so I checked it on my old Athearn PA2, read .80 amps just like it should.
  18. rogerw

    rogerw Active Member

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    Jeffrey can you swap the decoders around or are they hard wired with no plug?
  19. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    They're hard-wired. I already tried swapping them around yesterday. It was originally the B unit having the problem. I swapped the decoders around and now it's the A unit. This isn't a major problem, more a minor nuisance. I just give the units a little shot of DC then switch back to DCC and they both fire right up and they'll run all day long with no problem whatsoever.
  20. rogerw

    rogerw Active Member

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    So it sounds like a bad decoder. If you can live with it than I wouldnt worry about it.
    Edit: its a touchy decoder