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Diagnose Copper Wire Winding Faults

  1. Nov 4, 2012 #1

    I am wondering how I can diagnose a winding and find out whether it is damaged. Windings like for solenoids or electromagnets operating on 12VDC.

    Or even for 12V motors.

    I want to know how I can detect a turn to turn shorted winding. Does an electromagnet lose magnetic power and resistance when turns short? Like if I cut loops out of the winding then wouldn't it reduce the effective resistance and also reduce the inductance?

    What about heat? How can I tell if excessive heat is killing my winding?

    I am not that concerned about insulation failures because this is 12vdc.

    Maybe I am wrong but I would expect most of my problems to be heat and internal short related?

    An example is an ignition coil that arcs across itself and shorts out?

    I can test with a scope or multi meter or amp meter.

  2. jcsd
  3. Nov 5, 2012 #2
    Visual inspection should be the first thing done. Burned spots or melted copper is a sure sign of a short.

    And then there is always the old standby, replace the winding with a know good winding. If the new winding works, then the old winding is probably defective.

    Excessive temperature is usually indicated by an odor, the insulation may turn dark or have cracks, may be brittle or may flake off.

    This is probably not much help. I'm willing to bet that you knew all this already.

    Good Luck
  4. Nov 5, 2012 #3
    I have seen a shorted turns tester based on using the winding inductance and a fixed capacitance in an oscillator.

    A shorted turn or turns places excessive load on the oscillator and detunes it or even prevents oscillation.
  5. Nov 5, 2012 #4
    or just an LCR meter to measure DC resistance and inductance. Compare to a known good winding. If the winding gets damaged, these values should change.

    LCR meters basically perform the test proposed by Studiot in a hand-held instrument.
  6. Nov 5, 2012 #5


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    Do a ring test. A capacitor is placed in parallel with the inductor and the network is pulsed. A shorted turn will be indicated by severe dampening of the oscillation. A good inductor will have a number of oscillations before it decays off. Common method of testing flyback transformers and deflection yokes in CRT type televisions.
  7. Nov 5, 2012 #6
    I approve the damping measurement.

    Ignition coils (or was this only one example?) have thousands of turns so one short won't be seen on the DC resistance nor the inductance. But a shorted turn introduces significant losses that you've chances to see.

    And on an ignition coil, do expect failure from the insulator, sure. But you won't see nor even smell anything if just a turn is shorter (or rather: two layers are shorted, because votage between two turns is low). The available power is also a bit weak to produce important heat.
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