ohmmeter testing

Discussion in 'General Electronics Chat' started by gjo, Jun 8, 2013.

  1. gjo

    Thread Starter New Member

    May 22, 2013
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    In my book it says "use an ohmmeter for testing for open and shorted(internally and externally) field coils. What do they mean by internally and externally?
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Coil could be internally short (between the winding ) or some other externally component connect across the coli can also short the coil.
     
  3. gjo

    Thread Starter New Member

    May 22, 2013
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    Got it, thanks
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Ohmeters are not very good for checking wound components, apart from continuity and insulation resistance/shorting to case, because the wire has low resistance.

    A simple tester for shorted turns can be made that works on the principle that the impedance is reduced when turns are shorted. This loads down an oscillator reducing its action.
     
  5. #12

    Expert

    Nov 30, 2010
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    An external short might be some electrical continuity from the coil to the mechanical case of the machine.
     
  6. Gdrumm

    Distinguished Member

    Aug 29, 2008
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    Studiot,
    Can you explain the simple tester you described in more detail?
    Is it something one might build for a hobby shop?

    I work on scrapped things often, and the tester sounds like a timesaver.

    Thanks,
    Gary
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
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    A simple Colpitts oscillator can be constructed from two capacitors and any old coil that is lying around.

    Activity is monitored by a high z voltmeter or transistor boosted analog milliammeter.

    PM me with an email that can receive attachments for more.
     
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