Trains surging through switch tracks

Discussion in 'FAQs' started by douglasarcher, Aug 25, 2005.

  1. douglasarcher

    douglasarcher New Member

    I saw a thread about this somewhere, but after going through 450 threads, gave up. My layout is basically a loop within a loop. Each loop is connected by switches like in the attached diagram. When my trains go from one loop to another then there is a sudden surge forward before resuming the correct speed. Each loop is connected to a different power supply and the power is matched properly as it comes from one of those "2-in one" power packs. The red parts on the diagram are where I have my insulated joiners. I use a combination of Atlas Snap switches and identical switches by Bachmann. The normal ones which come with most starter train kits.

    I read somewhere else in this post that this can be eliminated by insulating only one of the tracks instead of both? Any information on this, or if you could simply guide me to the appropriate thread then I would appreciate it.

    Thanks in advance, Douglas

    Attached Files:

  2. steamhead

    steamhead Active Member


    I think your problem lies in the fact that as the loco moves acroos the insulated joint, it gets the voltage of BOTH powerpacks, that's why it surges. Once it's fully on the new track, it resumes normal speed since it's now being "fed" by one pack. What you need to do is divide your layout into several blocks, and use DPDT switches to "route" the power of ONE pack to the route your train is going to take.

    If you're unfamiliar with this system, I suggest you pick up one of the many wiring books to be had out there. Take a look at Kalmbach publications (the publishers of Model Railroader). They've got what you need.

    Hope this helps.

  3. 60103

    60103 Pooh Bah

    Insulating only one rail or wiring all the inner rails together won't work for you because you have the one power pack. These usually have only one transformer, so when you reverse one of the loops it will create a short circuit. (If your power supply has separate transformers, it may work.)
    Your simplest solution may be to isolate the two switches on the upper track (plus a section or two each side) and wire this as a separate block. Run this wire through a DPDT switch to choose which controller you want. Stop the train in the block and change controllers.
  4. GeorgeHO

    GeorgeHO Member


    I don't know anything for certain, but I have a guess as to what is happening.

    My guess is that your transformer has a center tap where it is splitting out the AC voltage into a positive portion for one side and a negative portion for the other side, and when your loco crosses so that one set of pickups are on one side its +12 volts, and the other side is picking up -12 volts, and the difference is 24 volts. Hence your loco surges until both pickups are on the same side. I beleive this might be called something like a false ground. You get the same thing in your household wiring. It you have a plug into one side of your fuse box, and another plug into the other side, and connect them together, say by a computer cable between your printer and console which has a bad ground, the potential (difference) between them is 240 volts instead of 120 volts.

    If that's the case, I don't think you can fix it without new equipment as suggested by the others (second xformer, cab control,etc).

    But I'm just guessing, i've been away from anything technical for a long time.
  5. ezdays

    ezdays Out AZ way

    The surge has to come from overvoltage. If you have a meter, disconnect both power pack outputs and turn up the voltage control to full. Measure the output of one, then the other and note what the polarity is on each output. Let's say you got 15 VDC on each one. Take the meter and measure the positive terminal of one to each of the terminals to the other output. If they two outputs are completely isolated, you should get no reading on the voltmeter. Do the same again from the negitive terminal of one to both terminals of the other. Again, there should be no reading. Like GeorgeHO is suggesting, if you get a reading, there is probably a short somewhere in the power pack, and you could get up to 30 volts between terminals if that's the case. Both outputs can run from one input (AC) transformer, but they must use separate output windings to run each DC output. I'm sure they were made that way, but they could have shorted together, or the outputs could have a common shorted together.

    Your best bet, use two indepentent power packs. This guarentees you that they will not short together.

    The best bet
  6. GeorgeHO

    GeorgeHO Member


    I couldn't sleep thinking about your problem and was going to say pretty much what ezdays said. When you do your tests with a volt meter, if it is not a center zero meter, run two tests and reverse your polarity the second time. If you don't have a volt meter, you could use a continuity tester, or a Christmas tree bulb in a socket with wires attached. Just see if the bulb glows brighter under certain conditions. especially when it should not be shining at all.

    If you take your engines off the track, you can do the tests right at the track without disconnecting anything.

    One thing that might correct the problem (but not really fix it) is to reverse the positive and negative leads on one side of your power pack, and also reverse the directional button at the same time. Test the results with your voltmeter, and if the power surge is on the same rail, it may have less of an effect on your locos depending on where their electrical pickups are. Just be careful you don't fry anything.
  7. ezdays

    ezdays Out AZ way

    I really think that everybody that's into MRR should have a meter. I've got several, mainly because we had an electronic manufacting business, but I've also bought a couple of really cheap digital meters so I can connect them permanantly to my power packs. I would recommend digital since it will determine polarity without switching leads. You can buy a basic meter that will measure AC and DC volts, AC and DC amps, continuity as well as resistance for between $10 and $20. The ones I bought were on sale at Harbor Freight for $3.00, regularly $6.00, and that's all you need. You can spend a lot more to get one that autoranges, has more ranges or features, but unless you're into electronics as a hobby or business, that's not necessary. Here's one I found at Harbor Freight for $5, ya can't beat the price. If you wan't better, they have better one there as well.
  8. brakie

    brakie Active Member

    For a easy solution use a Atlas selector and blocks..You see with the selector all you do is assign the block to cab "A"" or cab "B" and you locomotive will breeze though those switches with no problems...You will only need to insulate one rail with a selector..These selectors are easily wired and takes only minutes to install.
  9. santafewillie

    santafewillie Member

    Just found this post... forget all the stuff about meters and shorts...steamhead has the correct answer. You're getting power from two powerpacks at once. Do as brakie says and use some Atlas selectors and correctly align the switches (selector switches) and the problem will go away.
  10. steamhead

    steamhead Active Member

    Thanks Willie. I didn't want to toot my own horn, but as they say "been there-done that"- 'till my old man (PhD in Physics) came around and told me how it was done. So I followed his instructions (those above) and ...problem fixed.

  11. douglasarcher

    douglasarcher New Member

    Hi everyone,

    It's been a long time since I initially posted this thread. I really hate to leave my threads un-concluded, but I have now been able to solve the problem of my locomotives surging through turnouts. I never did manage to test the situation with an amp meter like some of you suggested. I recently bought a couple new power packs off eBay because I wanted an individual power source to operat my switches. Remember how I was using a "two in one" power pack and one of you said that the powerpack was not totally separating the ampage or soemthing like that? Well you were right (I don't understand much about electrical things), but when I connected my outside loop to the new power pack and my inside loop to one part of my "two-in-one" power pack the surging stopped. I was very surprised by that and still don't understand the technicalities of it, but now, all my locomotives (front truck and four truck pickups) go through the turnouts connecting the outer loop and inner loop smoothly without surging. So once again thanks to you all for providing me with advice on what to do. The problem is now solved.
  12. MasonJar

    MasonJar It's not rocket surgery


    Thanks for checking back in and letting us know that this (and your other question about reversing) have been solved. Often we (collectively) dispense a variety of advice without knowing the end result.


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