Using bigger wire!

Discussion in 'DCC & Electronics' started by Gary S., Aug 24, 2007.

  1. Gary S.

    Gary S. Senior Member

    I finished up my last shelves. The bus wires were #12 stranded, and were about 60 feet long from the command station to the end of the shelves. Well, the quarter trick didn't work. The command station would not shut down when the rails were shorted. Darn it, I guess that means another $150 for a booster for this section of shelves.

    Instead, I got some #6 copper wire and used that to feed the shelves. Presto, it all works fine now. However, I am a bit concerned about the length, I read somewhere that long runs can cause problems from induction and perhaps the "antenna" effect? Capacitance?

    But so far, so good.
  2. pgandw

    pgandw Active Member


    If you have problems with the long run - poor response or having to send repeat commands - search the common DCC sites (including Digitrax) for terminating the long runs. A highly conductive long run can have signal "reflections" from the far end due to the impedance mismatch. Installing a termination - usually a resistor and/or capacitor of the correct values across the bus wires will better match the system impedance and eliminate the reflections.

    Some large Digitrax layouts have had this issue, and resolved it with bus terminations.

    hope this helps
  3. Gary S.

    Gary S. Senior Member

    Fred, thanks for reminding me about that. I now remember having read about that at Loy's Toys or somewhere on the net. So far though, it has been working perfectly, no delayed response or anything. If I notice anything strange, i'll give it a shot.
  4. railwaybob

    railwaybob Member

    What make of command station do you have?

    What is the amperage of the command station?

    How have you connected your track feeders to the power buss - soldered or mechanical?

    What is the distance from one track feed to the other? (Track feeds should be about every 2' - 3')

    Do you have track feeds on the sidings?

    Do you have track feeds before and after each of your turnouts?

    If your power buss run is only 60', you shouldn't have any problems with track power.

    Bob M.
  5. Gary S.

    Gary S. Senior Member

    Make: Digitrax Empire Builder

    Amperage: 5 amps I believe

    The majority of the wiring connections are soldered, there are some on terminal strips, I used No-Ox electrical compound and tightened them down snugly.

    Track Feeds: Every section of flex track has its own feeder. So that is 3 feet max between feeders.

    Sidings: All fed seperately. I am not relying on rail joiners for any electrical connections whatsoever. Every seperate piece of track has its own feed, even those which are only 8 inches long.

    Turn-outs: All fed by feeders from the bus.

    I feel confident that the track is fed sufficiently. But I still had the problem of the command station not shutting down when I shorted the track at the furthest point. The #6 cured the problem.
  6. railwaybob

    railwaybob Member

    Hello Gary. I feel that somewhere along the line, you've got some poor connections. Your Empire Builder, at 5 amps, should be able to produce sufficient power at the end of your 60' of track buss to short across the coin - assuming you have a 5 amp transformer at a minimum of 12 maximum 22 volts AC as recommended in the Empire Builder manual. If you are in HO scale, I would suggest a minimum of 16 volts AC. Or, power your Empire Builder with the Digitrax PS515 power supply.

    What is the amperage of your power supply. While the Empire Builder is rated at 5 amps, if your transformer is producing a lower amperage or a voltage lower than the recommended voltage, your output from the command station won't be 5 amps. However, even if your output is, say, 3.5 amps, it should be more than sufficient to short the coin at the end of your track power buss.

    I would suggest that you solder all of your connections directly to your track power buss, rather than through terminal strips. It sounds as if you are using screw-down terminal strips. I've seen these types of terminal strips with bad connections. The difference in power output before soldering and after soldering made all of the difference in the world. Don't depend on mechanical terminal strips. For a technique that I use, visit this page on my website. Installing the Track Power Buss - Page 1

    The next steps will be to test your track power buss through the "process of elimination" technique using the "straight pin" process.

    • Shut off your Empire Builder.
    • Get two straight pins.
    • Go to the far end of your track power buss (at the 60' end).
    • Using a pair of pliers, insert one pin into the middle of one wire on your track power bus and the other pin into the other wire.
    • Make sure they aren't touching each other.
    • Turn on your Empire Builder
    • Touch the coin to both of the pins to short them out.
    • Your Empire Builder should shut down.

    • [*]If your Empire Builder doesn't shut down, go to the 30' mark (half of your 60' track power buss) and repeat the "straight pin" process.
      [*]If the EB shuts down, then move to the 45' mark (half of half) and repeat the process.
      [*]If the EB doesn't shut down, move to the 15' mark (half of half) and repeat the process.
      [*]Keep repeating the process until your EB shuts down.

    If you end up at the Empire Builder before it shuts down, you probably have a problem at the Empire Builder.

    Let me know how it works and we will then take you through the next steps in trying to fix your problem.
  7. Harold Cole

    Harold Cole Member

    I have several 60' runs and am running #10 wire to power my feeders.Digitrax Chief is my command station and once in a while was having problems and fon=und the problems were due to inductance.Went to radio shack and bought Ferrit bead Inductors and that solved all the problems.
  8. railwaybob

    railwaybob Member

    Did you twist the wires on your track power buss? That will cause inductance. The track power buss wires should each be run in a straight line, keeping any crossovers to a minimum. A few cross-overs are okay but twisted wires are not.

    On 60' runs, soldered joints, and 12 AWG stranded wire, you should not have any problems and should not need any ferrite inductors. Just to make sure we're talking about the same thing, 12 AWG wire is a bit thicker (about 3/16") than the wire used in your house wiring.

    Bob M.
  9. TCH

    TCH Member

    just a question for the experts.

    if the command station was situated in the middle of the layout and went
    30 ft in each direction would that be better ?
  10. railwaybob

    railwaybob Member

    Yes, if the command station was located in the middle, it would mean a shorter run for the track power buss. Theoretically, voltage drops with the length of the run.

    However, I think Gary's problem is something other than the length of the run of his track power buss. At Ottawa Valley HOTRAK, we are doing runs that are over 75' in length just from the central location of our command station/ boosters to a power district. And then we have another 30' - 50' of model railroad modules that are connected together - ie 100' - 125' from the command station/ boosters to the farthest track - and we don't have any voltage drop problems. All on 14 AWG wire.

    Bob M.
  11. baldwinjl

    baldwinjl Member

    I believe this to be untrue. In fact, I think one of the manufacturers (NCE, I think) recommends 3 or 4 twists per foot on the track bus. The theory is that by twisting the track bus both wires are subject to the same outside interference, so at the end of the day, it cancels itself out, since the DCC signal is differential. My personal opinion is that with the level of the DCC signal it doesn't make a hill of beans of difference, but it can't hurt.

    A 60 foot run is pretty long (120 feet out and back), but with 12 gauge it should be fine, I think. I agree, look for bad connections, or other problems.

  12. JR&Son

    JR&Son Member

    On computer networks, the wires must be twisted to stop interference. Not really sure of the DCC process, just wanted to add my 2 cents worth.

  13. railwaybob

    railwaybob Member

    For a full discussion on whether to twist or not to twist, look up some of the old discussions on the Digitrax@Yahoogroups forum.
  14. ChadYelland

    ChadYelland Member

    I have a book on DCC by model railroader, i noticed it says in there to keep the bus wires straight and parallel but I too have heard of this twisting for interferance reasons, allso I was told that you can not install a capacitor across the bus wires as it i guess you'd say absorbs the DCC signal???
  15. baldwinjl

    baldwinjl Member

    Generally all true. IMO, twisting is really a non-issue either way, though tight twisting might be a problem. A cap across the bus wires willseriously mess up the edges of the signal, quite possibly throwing it out of spec.

    Here is the termination NCE recommends on longs runs:

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