Solenoid

Discussion in 'General Electronics Chat' started by qitara, Aug 14, 2013.

  1. qitara

    Thread Starter Member

    Jan 18, 2013
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    Hi folks

    how is a solenoid tested, is it possible to megger it ?


    Got a bad 110Vdc solenoid that I want to test, but using a multimeter I don't see any change in the ohm reading, I think this is due to the multimeter not supplying enough voltage to the solenoid to detect the fault, so is there another way to test it ?


    The solenoid is bad because when energized it draws to much current and causes indication lamps that is supplied from the same power source to dim.
     
  2. #12

    Expert

    Nov 30, 2010
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    That last sentence is a valid test. Failure to work under the conditions it is supposed to work in is a dead give away. Apply rated voltage and see if the current is too high.

    Then, there is a ringing test to find internal shorts. The, "growler" test involves inflicting a power line frequency magnetic field on the coil to see if it loads down the magnetic field.

    I'll bet there are methods I didn't think of.
     
    Last edited: Aug 15, 2013
  3. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    The reason the multimeter Ohms range won't see the problem is that a shorted turn (or several) will not affect the DC resistance enough to be visible.
    It will,however,affect the inductance of the winding,& in turn,its ability to move the core,
     
  4. qitara

    Thread Starter Member

    Jan 18, 2013
    87
    0
    Is there any ohm meter that supplies high voltages like a megger do to test such problems ?
     
  5. qitara

    Thread Starter Member

    Jan 18, 2013
    87
    0
    Just magnetic wire wounded around an iron core.
     
  6. #12

    Expert

    Nov 30, 2010
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    That might be enough, but, shorted turns while stressed by the rated voltage is the test I believe in. Unfortunately, ohm meters don't go that high.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A bit of a contradiction, your meter shows open yet it draws excessive current??
    A normal VOM should be up to the job, usually the only misleading reading is when testing S.S. components on the Ohms scale.
    The normal resistance range for a 110vdc pneumatic or Hyd. solenoid is around 700-500ohms on average.
    A couple of things come to mind, are you sure it is a DC solenoid?
    An AC solenoid of the same voltage rating is much lower in resistance.
    If it has been in circuit for some time it could be an internal reverse EMF diode shorted, or if fitted with a diode could have been connected up in reverse?
    Max.
     
  8. #12

    Expert

    Nov 30, 2010
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    I don't think he said, "open".
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I took 'no change in ohm reading' to mean no indication on his meter?
    Not that clear why he would expect a change??
    Max.
     
  10. vk6zgo

    Active Member

    Jul 21, 2012
    677
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    I went with the fact that it is not possible to determine shorted turns on transformers & chokes with an Ohmmeter,as the change in resistance is such a small percentage of the total.
    A shorted turn is enough to render a transformer or choke unusable.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Although more likely to have much greater effect on a AC inductive device, an adjacent shorted turn on a DC device is much less affected.
    Max.
     
  12. qitara

    Thread Starter Member

    Jan 18, 2013
    87
    0
    Its a 900W DC solenoid coil that runs on 110VDC as specified, its used in a vacuum circuit breaker to de latch the contacts.

    using my ohm meter I get 12,3 Ohms, that is the same reading I get when measuring the good coils on the other breaker we got installed, but this one dims all the indication lamps and causes a voltage drop when energized.

    Will this Work ?, I was thinking about supplying the coil with 110VDC and measure the current and calculate the wattage using ohms law and see where the values ends up
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The resistance will give you the current exactly on DC.
    So 900w & 12.3 ohms is about correct?
    110/12.3 = 8.94a
    Comes 0ut to 983w however.
    Max.
     
  14. #12

    Expert

    Nov 30, 2010
    16,298
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    Measuring the current is a way to see if this solenoid is different from the others, as compared to it trying to work properly in a circuit that has a bad connection that is restricting the available current. (That means, "yes".) It would be a good double check to measure a known good solenoid. I figure the current should be about 8.2 amps.
     
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