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Non Polar Capacitors -- Inconsistent Meter Tests

Discussion in 'Troubleshooting and Repair' started by Bud, May 31, 2017.

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  1. Bud

    Bud

    16
    2
    May 31, 2017
    Hi All,

    I'm repairing an amplifier and decided to replace some of the non-polar capacitors. Out of curiosity, I'm testing all the ones I pull out. When I test them in my meter, I can insert the legs either way into the tester and I get a valid reading.

    The replacement caps I bought are the same capacity, same voltage, same radial can, everything. They are clearly marked "non-polar." However, when I test them prior to installing them in the circuit, the meter will only give a valid reading when the legs are inserted in a given direction. That is, it's *behaving* as if it's a polar cap.

    Is this normal? What causes this? My hypothesis is because the cap is unused and therefore was shipped with some polarization. But I have no clue.

    Any ideas?

    Thanks,
    Bud
     
  2. davenn

    davenn Moderator

    13,880
    1,964
    Sep 5, 2009
    Hi Bud
    welcome to EP :)

    what sort of meter ?
     
  3. Bud

    Bud

    16
    2
    May 31, 2017
    Thank you. It's an NRI Digital Multimeter.

    I tried putting a charge on one of the new caps and then testing. That worked, though I'm still not sure why. I think is has something to do with the fact they're new.

    I'm fixing my old Sunn Beta Lead guitar amp. Maybe I'll start a new thread on that, as I'm having some trouble getting it going.

    Thanks for answering!

    Peace,
    Bud
     
  4. davenn

    davenn Moderator

    13,880
    1,964
    Sep 5, 2009
    sorry, that didn't really help, when I googled that I got fluke multimeters ...
    got a link to one please ....
    does your meter actually have a capacitance tester built in or are you doing some other sort of odd-ball test method ?


    Dave
     
  5. Bud

    Bud

    16
    2
    May 31, 2017
    Hi Dave,

    It's an old meter, so I can't find a link to it or even a photo of it. But it's a good meter and has a good built-in cap tester that works great. The new caps *acting* polarized was just something I'd never noticed before. Probably because I don't usually test new caps. Once I charge the cap with a 9v battery, it behaves like any other NP cap in the meter. Just a weird thing, I guess.

    Thanks for your interest!
    Bud
     
  6. davenn

    davenn Moderator

    13,880
    1,964
    Sep 5, 2009
    why are you charging the cap before testing ?? you shouldn't be .... that's a great way to damage your meter

    the cap should be uncharged (un energised is a more accurate term) before connecting it to the meter
     
  7. Bud

    Bud

    16
    2
    May 31, 2017
    Hi Dave,

    I didn't mean to imply that it remained energized during the test. For whatever reason, a cap right off the strip will only test in one direction. But if I put it through an energize-discharge cycle then if behaves as any other NP cap I've ever tested. I tried a few more right off the strip today as I was working and some of them *did* behave normally--without my first putting them through a cycle. I think it's just a quirk of the meter.
     
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