How to electronically determine polarity of charged capacitor ?

Could some electronics guru please help ? How would one electronically determine the polarity of the plates of a charged capacitor ? Any hints, suggestions would be helpful.

Reply to
Daku
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A DC voltmeter? Is it over 50 volts?

George H.

Reply to
George Herold

I read it to ask if there was a way to design a meter of some kind that could let someone attach two leads to an electrolytic capacitor (or any other type that might also be polarized) and that it could automatically determine which of the two leads was (+) and which was (-) so that the operator could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something that would monitor the rate of change of capacitance vs impressed voltage, etc?

Jon

Reply to
Jon Kirwan

Yes, that makes more sense; instead of 'a charged capacitor'=20 it would be 'a poled electrolytic capacitor'.

There's one way: the leakage should be greater in the 'wrong' direction, so an AC source (transformer-coupled, you cannot allow any DC for this) connected to the capacitor, and a good DC meter, should show you the 'right' polarity. =20

Reply to
whit3rd

I read it to ask if there was a way to design a meter of some kind that could let someone attach two leads to an electrolytic capacitor (or any other type that might also be polarized) and that it could automatically determine which of the two leads was (+) and which was (-) so that the operator could be told, not guess about it.

Perhaps some kind of low voltage leakage test or something that would monitor the rate of change of capacitance vs impressed voltage, etc?

Jon

The OP didn't ask about a shelf capacitor, "charged capacitor" was the question. DC voltmeter is still the answer. Tom

Reply to
Tom Biasi

Any ordinary DVM will give you this. If the red lead is more negative than the positive lead, then the display will show a minus sign ('-') at the left end of the digits. (and, of course, the digits will tell you how many volts the DUT is charged to.)

Hope This Helps! Rich

Reply to
Rich Grise

So, do you ever plan to come back to look for answers, or are you waiting for the answer fairy to leave them under your pillow?

Thanks, Rich

Reply to
Rich Grise

Geesh, OK you can read whatever you like into the question. But it's easy to determine the polarity of a "charged capacitor". I think I'm starting to sound like Phil A. Pretty soon I'll be cussing like a banshee.

George H.

Reply to
George Herold

Thanks for each of your responses. In my original post, when I said "electronically" what I had in mind was an in-circuit automated sub-circuit that would periodically check the plate polarities of a capacitor, and set a flag, for example depending on the polarity of a specified plate. I mean, the capacitor might be getting charged/discharged by some unknown waveform, and all we want is to know the polarity of a specified plate at periodic intervals.

I wish there was an answer fairy. Then, I could ask the questi>

Reply to
Daku

[top-post repaired]

Yes, of course. Just use any differential-input bipolar ADC, that your software can read at its leisure.

And don't top post, and try to get off google; this is USENET, not "google groups." Preferably, get a real news server - your ISP might offer one; I use eternal-september.org - and a real news reader program.

Good Luck! Rich

Reply to
Rich Grise

--
Banshees don't cuss, they wail. ;)

http://en.wikipedia.org/wiki/Banshee
Reply to
John Fields

Use a comparator with one input connected to the specified plate of the cap, and the other input connected to the reference voltage. The comparator output will change from high to low (or low to high) whenever the plate of the cap changes polarity, even if the plate is only slightly above or slightly below the reference. You can poll that flag at whatever intervals you need - the flag will always indicate the polarity per your definition. You'll also need to define what happens in response to the flag when it is polled - does an LED light, does an alarm sound, does some other sub-circuit get reset, whatever.

If you need a range of voltage, use a window comparator. Your definition of polarity determines both the reference voltage level, and the range. For example, you might call anything above 3 volts positive, and anything below 2.5 volts negative.

Ed

Reply to
ehsjr

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