Non Polar Capacitors -- Inconsistent Meter Tests

[Bud]

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

 

[davenn]

Hi Bud
welcome to EP

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.

what sort of meter ?

 

[Bud]

Hi Bud
welcome to EP

what sort of meter ?

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

 

[davenn]

It's an NRI Digital Multimeter.

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

 

[Bud]

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

 

[davenn]

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.

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

 

[Bud]

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.