Electrolytic caps lying?

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kimko

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I need to check (out of circuit) caps. My "Extech" digital multimeter has that feature. When I use the meter the zero level is 0.084nF due to probe cord, I presume. When I measure 1000, 1500, & 2200 uF caps the meter reads 0.206 to 0.268nF. This cannot be correct! Is my problem that the electrolytic is talking back at me? Seems I recall that in my dim past that electrolytics lie when measured. How can I measure these buggers?
 

I would first check a manual for your meter to see what it's capacitance measurement ranges are. And your 'zero level' doesn't sound right, most multimeters with cap functions I have seen clearly show when there is no capacitor hooked to the leads. And electrolytics should be no problem to measure if within range of the meter.

I would test your meter with some known good caps of various valuesand see if it responds as it should.

Lefty
 
If a 100nf ceramic cap reads OK, then the meter is probably OK. Most electrolytics need a DC bias to function properly; does your meter provide one and are you connecting the cap with the proper polarity?
 
My Fluke gives no reading with nothing connected, only goes down to 1nF, but will measure up to a few tens of thousands of uF's correctly. I would check polarity first then ranging.
 
Hare you sure your meter works properly for such large values?

Most meters only go up to 20:mu:F or so.
 
Dawny,
Your meter is correctly showing the capacitance of its input and its leads.
 
Don't forget about the tolerances! you could get a 100uf cap with -20+80% tolerances, so it could be way off. Still I agree with that the meter may not be able to handle that high of tolerances.
 
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