Calling all electrical people, finding a short

Discussion in 'Power - Site Power/Batteries/Generators/Solar' started by mschepac, Aug 13, 2017.

  1. mschepac

    mschepac South Jersey

    Apr 22, 2008
    South Jersey
    A friend of mine has a travel trailer. We have discovered that he has a short that we cant find. We have done some internet research with no luck finding it. Here is some of the details so maybe you fine folks can help us.
    The camper is not connected to shore power.
    When we disconnect the negative cable from the battery and place a volt meter between the negative cable and the negative lug of the battery we get 12v.
    All of the posts that we found on the subject suggest that removing the fuses one at a time should indicate which circuit the short is on. After removing all of the fuses from the converter, we still have 12v.
    We have tried to disconnect each of the wires on the 12v load side of the fuses, with most of them off we get about 9v. Once they are all disconnected we have about 1.5v.
    Again most of the posts on this subject suggest that if "a fuse keeps blowing", none of the fuses are blowing.
    He tried removing all of the exterior light bulbs as well, strange suggestion but we thought we would give it a try as well.
    I am sure there are many other combinations of un-wiring and re-wiring that we have tried that would be too much to list.
    Any help or suggestions would be appreciated.
  2. jmkay1

    jmkay1 2004 Fleetwood/Coleman Utah

    Oct 10, 2013
    Northern Virginia
    Sorry not too much help, but have you verified the wires are not frayed anywhere. That ended up being my problem. Everything worked on shore power but nothing worked on 12v. I lucked out and saw a spark at the connector to the camper and discovered the bad wires after trying to follow the wires from the battery to the converter.
  3. SteveP

    SteveP Active Member

    May 21, 2015
    Any camper battery tested in that way will show battery voltage due to parasitic draws, at least from the propane detector. Since it is a TT there are probably other parasitic draws as well. This by itself is not an indication of a short.

    Why did you originally think you had a short, what prompted you to begin testing.
    Lloyd B likes this.
  4. neighbormike

    neighbormike Well-Known Member

    Oct 6, 2012
    The battery has 12v. You are completing the circuit with your meter/ just checking voltage. If you're worried about a draw, use an ammeter. Leave the negative disconnected, connect pos lead of meter to neg battery terminal, connect neg lead to neg wire....
  5. WeRJuliIan

    WeRJuliIan If it's "Aluminum", why not "Sodum" and "Uranum"?

    May 15, 2014
    Sarasota, FL
    If none of the fuses are blowing, what made you suspect a short?
    Not to be rude, but your measurements are probably confusing you.
    Interrupt a circuit and you'll get a voltage difference across the gap... that's what you're measuring.
    As has been suggested, you should be measuring the current, to see if it's excessive, or appropriate to whatever is connected.
    Last edited: Aug 13, 2017
    NMroamer likes this.
  6. NMroamer

    NMroamer Active Member

    Apr 21, 2016
    Albuquerque NM
    What he said. You might not have a short.
  7. tombiasi

    tombiasi Well-Known Member

    Sep 1, 2012
    Northwestern New Jersey
    If the fuses are not blowing you don't have a short. Unless you are incorrectly using the term to mean a malfunction. What's happening that is causing you to do all this testing?
  8. mschepac

    mschepac South Jersey

    Apr 22, 2008
    South Jersey
    We have checked two other different campers with the negative wire to negative post with zero volts. Not since we have been testing, but prior to this, his slides and awning would not work properly. At one point he had disconnected the battery. When he tried to connect it, it was arcing badly. If all of the fuses are pulled from the converter, there is no parasitic draw.
  9. NMroamer

    NMroamer Active Member

    Apr 21, 2016
    Albuquerque NM
    Sounds like the current draw is significant and bypassing the converter. To prove this disconnect the converter from the battery. Isolation is the best way to track the problem which you have already started to do.
  10. Douggro

    Douggro Active Member

    Jul 26, 2017
    Seattle, WA
    Completing the circuit, yes, which would be continuity. For there to be a voltage reading, the negative side has to have an open connection to the positive side, aka a short.

    One thing that leaps to mind that could be causing this is a faulty unit that uses PWM or a modulated ground for a circuit and has a minor short in it, rather than a full dead-short.
  11. SteveP

    SteveP Active Member

    May 21, 2015
    "his slides and awning would not work properly" That's the place to start. How many circuits are involved with the slides and awnings.

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