Measuring ohms in transformer winding

Discussion in 'General Electronics Chat' started by Alan fay, Mar 30, 2015.

  1. Alan fay

    Thread Starter New Member

    Mar 30, 2015
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    What should an ohmmeter measure across the input leads of a transformer?
     
  2. MCU88

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    Mar 12, 2015
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    Very low DC resistance. But not too low as the wire turns might be shorted if this is the case.
     
  3. MrChips

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    Oct 2, 2009
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    It depends on the transformer.
    What is the primary:secondary turns ratio?
    What is the voltage/current/wattage rating of the transformer?
    Are you measuring across the primary or secondary windings?
     
  4. Alan fay

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    Mar 30, 2015
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    I measure 57 ohms across both the input and output leads of a transformer the input is 110 volts.i think it is an isolation transformer.does this sound right?
     
  5. MrChips

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    So you don't know if it is step up or step down?

    Find a low voltage AC/AC adapter. For example, one that puts out 12VAC from AC mains.
    Use this lower voltage to test your unknown transformer. This would be a safer test than attempting to put full 120VAC across an unknown transformer.
     
  6. Alan fay

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    Mar 30, 2015
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  7. #12

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    Nov 30, 2010
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    Fifty-seven ohms seems a bit high. This would be compatible with a small transformer, around one amp.
     
  8. Alan fay

    Thread Starter New Member

    Mar 30, 2015
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    If the primary is simply a coil of wire and the ohmmeter sends a cd voltage,thus no induced reverse emf,shouldn't
    The resistance be close to zero?
     
  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    What are the transformer's general dimensions?
     
  10. Papabravo

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    Feb 24, 2006
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    The resistance of the winding depends on the wire guage used to fabricate the winding. In order to get a large number of turns on the primary winding you have to use a small diameter wire. AWG #30 for example is 103 ohms per 1000'
     
  11. Alan fay

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    Mar 30, 2015
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    It s small. About 2.5inchesx2in. What difference does the size make?if it's just wire wound in a coil with no reverse emf why isn't it just like measuring a strait piece of wire?
     
  12. Papabravo

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    Feb 24, 2006
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    So 553' of AWG #30 wire would give you 57 Ω
     
  13. cmartinez

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    The size is important because it will give you an idea of how much power it can handle.
    Also, accurately measuring a winding in a transformer is a bit tricky, since a voltmeter normally pumps a little current into what it's measuring, and that current in an inductor can cause fluctuation readings.
    Anyway, Papabravo's observations are important... can you measure the winding's wire diameter? Do both windings use the same wire size?
     
  14. Alan fay

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    Mar 30, 2015
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    Both responses answered my question thank you very much
     
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