Are film capacitors directional?

Hey Al....once again, thanks for your valuable input on all technical subjects. I don't mean to sidetrack this thread - but since audiogon disabled the ability to communicate otherwise I'd like to ask & hopefully this is valuable to others as well...is it worth buying a really quality grade multimeter? I've used a $20 Radio Shack digital multimeter for years to bias my amps & often wondered if I'd get different readings from a better grade meter?

Hi Pehare,

Thanks! I don't know the answer to your question, though, as I haven't ever used a RS DMM. FWIW I did use a RS FET-input (high input impedance) analog multimeter many years ago, and it seemed to work well, and lasted a long time.

If the opportunity arises, perhaps you could borrow a Fluke or other good meter from someone, and compare readings.

Believe it or not, the only meter I've had here in recent years is a not particularly accurate Triplett analog multimeter, supporting both my audio and antique radio endeavors. I do have a low end oscilloscope, though. I'll have to get myself a good Fluke DMM at some point, probably one that also measures capacitance and perhaps inductance as well.

Best regards,
-- Al

Thanks, Al! Very helpful. I bought a better meter today, so I will try the procedure you described tomorrow and report back.

Bryon

Okay, Al, I think I'm following your instructions exactly, but I'm not getting consistent results. I've tried several different capacitors, and I get a different reading every time. Don't know what I'm doing wrong...

-I checked the outlet and it is definitely grounded.
-I've drained the capacitors by connecting a wire between the two leads and then taken readings.
-I'm using clips to ensure that I have a good connection.
-I've draped power cords from 2 different devices over the caps.

...and still I get constantly changing results. Some of the time, the meter WILL come to rest on a specific number. But when I remove the meter's leads and check again, the number is different. Sometimes the number is positive, sometimes negative, even for the SAME end of a cap. I'm confused. Any ideas?

Bryon

Hi Bryon,

Are you using a setting for AC (not DC) volts? Not sure how you could sometimes be getting a negative number for AC volts.

Also, charge that is stored in a capacitor can sometimes "bounce back" to some extent after a connection that has been used to discharge it has been removed. That can occur as a result of what is known as dielectric absorption. So it would be a good idea after discharging the cap to use the meter to verify that no DC voltage exists across it.

Beyond that, it may be a good idea to tape the power cord in place on the capacitor, to be sure that its exact position relative to the capacitor doesn't change as the leads are being removed and applied. And also try to keep the test leads as far away as possible from the power cord.

Also, let us know the make and model of the meter, and I'll try to take a look at its description, which might give me some further ideas.

Best,
-- Al