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What am I seeing? (electrical problem)

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  • What am I seeing? (electrical problem)

    I tried to run the train the other night after about a two month absence. Nothing. Started testing with the meter and eventually found that the two rails are showing a short. I have a single loop of track. No turnouts or other wiring complications.

    A digital meter shows a short with about -500 ohms with the common lead on one rail. If I switch leads the meter shows open. With an analog meter I show about 500 ohms regardless of which lead is on which rail.

    The track has been in place for about one year. It's brass, code 332, with plastic ties. I have vacuumed the ballast out from around the area where the problem seems to be occurring. I narrowed the problem area down to this location by raising the track onto wood blocks and then removing the blocks one at a time until I found the location where the short reappeared.

    Some times if I move the track, the short will disappear, only to reappear a couple minutes later. I have put the meter on the track while raising the track and the meter still shows a short. If I remove the leads and retest a couple minutes later, the short is gone.

    I am completely stumped by this behavior. Any ideas or suggestions would be greatly appreciated.

    Tom

    edit to add: I did not have the power supply connected while testing.

  • #2
    It sounds like you've got a conductive rock in amongst your ballast? Or a bit of fence wire or something? If it doesn't short when it's up in the air, but does when it's down on the ground, that sounds like what it's sitting on, not the track itself. Unless there was some sort of molding problem with the ties, and one of them wound up with a bit of wire inside the plastic.
    James

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    • #3
      Hi, James.

      The track has been running for about a year so i don't think there's a problem with the ties. I also thought of conductive rock (stranger things have happened). That's why I vacuumed out all the ballast in the area. Right now about my only option is to start cutting the track to see if I can isolate the area.

      Tom

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      • #4
        Have you tried testing voltage on the track. 500 ohms is not a short but sounds like a throttle attached when you tested for ohms. Start by checking output voltage from your throttle not connected to the track. Once voltage has been established, connect the throttle to the track. See where you loss voltage.

        Dave Silvernail

        Northern California Narrow Gaugers

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        • #5
          Good morning, Dave.

          The power supply is not connected to the track, nor is there any rolling stock on the track. In such a scenario, there should be no circuit when the leads are placed on the track. That's what's so puzzling about this. I also removed the power connector from the track. I'm showing about 15 volts through the connector and a short on the track. As mentioned above, I'm going to have to start isolating sections of track until I find it.

          Tom

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          • #6
            Are there any power feeders at that point? Could they be the cause of the short?

            I don't quite follow what you are saying with the wooden blocks? How does that help find the short?
            Built a waterfront HO layout in Ireland http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=22161 but now making a start in On30 in Australia http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=52273

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            • #7
              Hi, Neil.

              There is only one set of power feeders and I even disconnected those while testing for the short.

              As to the wooden blocks, I slid them under the rails and ties to completely lift the track off the ground. I was about a third of the way around the track when I decided to test again. That's when i found the short had disappeared. I started removing the blocks of wood and putting the track back on the ground until the short reappeared.

              Tom

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              • #8
                is it sectional track? Could something in the roadbed be causing a short? If you lift the track up, put a sheet of paper under the track and put it back down is there still a problem?
                Built a waterfront HO layout in Ireland http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=22161 but now making a start in On30 in Australia http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=52273

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                • #9
                  I guess I fixed it. I went out this afternoon armed with meters, plastic bags (to put under the track to isolate it from the ground), and a determination to find the problem. Put the meter on the track and all showed good. Got the train out and it ran like a champ. Go figure.

                  At this point the only solution I can think of is that there is dirt somewhere that has dried enough to eliminate the short. I may soak the track good with the hose and see if the problem reoccurs.

                  Thanks to everyone who contributed ideas, suggestions, questions, or silliness (I've had some of that in some of the forums). Your contributions are all greatly appreciated.


                  Tom (still scratching his head)

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