Two More Questions

Discussion in 'FAQs' started by Play-Doh, Sep 24, 2007.

  1. Play-Doh

    Play-Doh Member

    Im deep into the wiring jungle. Well, im getting ready to enter the jungle. But before I do, I have to remind myself how little about it I actually know. Im learning as much as I can before bothering you fine folks.

    However, I do have two questions.

    1. what is the general rule for how many points of contact I should have with my rail from the power pack? I said that totally wrong. I guess my question is, by the time my trains get 50 feet away from the power point, does the voltage drop? Is there a equation to figure how many leads you need to connect to the rail? Is one enough? Of course I undertand each block must have its own lead, but what if that block is HUGE? I hope that makes sense.

    2. What is the reommended gauge wire for primary power in HO DC layout?

    Thanks ahead of time. I have yard updates comming really soon!

  2. pgandw

    pgandw Active Member

    The answers really vary, depending on what you are trying to accomplish. A few points which play into the answer:

    1) Rail joiners tend to be unreliable conductors of power over the long term. This would suggest that optimum reliability comes from either soldered rail joints and/or feeders for each section of rail. That can be a lot of work, so usually a compromise is made. Typically, feeders every other section of flex track and soldered rail joints on curves (to help mechanical alignment as well as electrical conductivity) is the conservative recommendation.

    2) Voltage drop depends on current drawn, and distance of the run, for a given gauge of wire. In DC, voltage drop is not all that critical unless you are running at just above locomotive slow stall speed. In DCC, voltage drops of greater than 5% (0.7 volts) can cause decoders to stop responding correctly. A typical HO locmotive draws less than 0.5 amps running; most newer locomotives are around half of that.

    3) Proper and safe operation of circuit breakers or current limiting trips depends on the wiring passing the minimum current to cause these devices to trip. In other words, if your DCC system can put out 5 amps, then your wiring must be capable of passing 5 amps all day without overheating or causing excess resistance that would cause the breaker not to trip.

    In DCC, the quarter test is frequently used. Laying a quarter across the track should cause the system circuit breaker to trip immediately. If it doesn't, the wiring isn't robust enough.

    Since most DC power packs cannot put out more than 1-2 amps, wiring can be smaller gauge than for DCC.

    In open air conditions, 20 gauge wire can handle 5 amps; 24 gauge wire 2.5 amps, and 28 gauge wire 1 amp. But keeping voltage drops within limits for a double-headed train usually requires a larger gauge wire. Typically 20-24 gauge wire is used for short (less than 18") feeder connections directly to the rails, although I have successfully used 26 gauge to every piece of rail on small layouts. This is then tied to larger gauge wire, 18 gauge for DC and 14-16 gauge for DCC, for the longer distances.

    12 and 14 gauge wire is easily found at reasonable prices (used in household wiring), and so is often used for DCC power buss.

    Hope this makes sense and helps
  3. 60103

    60103 Pooh Bah

    If you have a long block, the several lighter feeders will work in parallel and overcome the problems with rail joiners (for a while). The load on DC wires will normally be only one loco or consist, so you don't need the size of DCC wires where they can be powering all 1000 of your railways locos at once. <smile>
    With DC you will often have a lot of smaller blocks for flexibility.

    We had a situation (DCC) where one of the main feeders had become detached from the bus and a whole section of layout was being powered through a single feeder at the far end of one block; there was a dodgy rail joiner in that block and we had the section shut down at odd times -- when a loco was going over that rail joint.
  4. Play-Doh

    Play-Doh Member

    Thank you for your help! To answer your question, I already solder all my rail joints. I have since I started, it just seems easier (plus I love to solder!).

    I think I will add feeders to various parts of my layout. It will certainly help operations as well as narrowing down trouble spots when they come up.

    Thank you for your help!
  5. Gary S.

    Gary S. Senior Member

    My thoughts for what it is worth, and it may certainly be overkill, but I wasn't willing to take any chances:

    1. Don't solder the joiners to allow for any expansion and contraction of the benchwork. (Unless it is two short pieces of track, or perhaps a turnout can be soldered onto a piece of flex track)

    2. Every piece of track between rail joiners needs a feeder from underneath. Every piece of flextrack, every turn-out, even short pieces to fit stuff together. (yes, that is alot of feeder wires, but if ya love to solder, it may as well be track feeders)

    3. Power the frogs of Atlas turn-outs.

    4. Atlas turn-outs need some jumpers from the rails to the points. This can be done from underneath the turn-out before it is installed. Or, if already installed, it can still be done form above.
  6. Play-Doh

    Play-Doh Member

    I thank you for the quick reply! It was most helpfull.

    One more question.

    Take a look at my trackplan. (Please ignore my self notes)

    As you can see, I have set this up for DC and have the yard seperated from the main layout with blocks so that the train can re-approach and enter the yard after making it around the layout. Now, since the yard is its own block, and on seperate power, im going to need to install a DPDT switch in order for the train to keep moving forward, right? In other words, once the train leaves the block (yard) throw a DPDT and then when it hits the yard again from the other approach track it should keep going, right?
  7. 60103

    60103 Pooh Bah

    Yep, the yard constitutes one leg of a wye and is probably the most logical bit to be separated. You need 2 separate reverse switches -- one for the yard and one for the loop. (Your turntable may need one too, depending on how it's wired.)

    With this layout, you may want to consider cab wiring to allow you to run more than one train at once, especially with that roundhouse and the separate loop.
  8. Play-Doh

    Play-Doh Member

    Thank you so much! OK, another question. (hopefully the last for a while)

    Ok, This a stupid question. I mean, I should already know this. But id rather ask and be sure before I fry my engine.

    Ive alway ran my train on my loop (ive already built the upper piece with the inner loop) counter clockwise.

    Now if I were to turn the engine around it will still run correctly, correct? However the reason I need the DPDT switches is because when it hits the block the polarity must be the same as the previous block, correct?

    So in otherwords the train can operate no matter which way its faced on the polarity, but only unless its at a dead stop before moving. I hope that makes sense. I thank you for your patience, im still learning so much.
  9. 60103

    60103 Pooh Bah

    A DC train will run the same way on the track, no matter which way it's facing. If you have it running CCW, pick it up and turn it around and it still runs CCW. (Under DCC it runs fwd even after you pick it up and turn it around).
    I think the Standard is that as you face forward, it will run forward if the RH rail is positive. So when you turn it around, the LH rail is now positive so it runs backwards.

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