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What readings to expect from a DMM's Cap setting

KilgoreCemetery

Apr 12, 2017
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I have a complete rookie question about this Digital Multimeter I just bought. It's a Southwire 10040N and it has a CAP function that reads in microfarads, nanofarads, etc. The confusing thing is, most of the time when I check capacitors I get wildly different readings than what is listed on the capacitor itself. I have been checking them out of circuit, but I can't believe that all the ones I've checked so far have been bad. I'll give some examples in the hopes that someone can either tell me what I'm doing wrong or explain whether or not I'm getting the correct readings.

Cap A: 400v 180uF 105c -> .02nF before going to 0L
Cap B: 400v 180uF 105c -> .02nF before going to 0L
Cap C: 35v 1000uF 85c -> .03nF before going to 0L
Cap D: 10v 22uF 85c -> 41.75uF
Cap E: 15v 150uF 85c -> .03nF before going to 0L

This all makes me think that maybe there is something wrong with the multimeter itself, until I tested an old AC capacitor with it.

Cap F: GE Z25L4403 240v 10/25uf. Going from "HERM" to "C" -> 24.48uF, "C" to "FAN" -> 10.15uF

I don't know anything about AC capacitors, but it seems like more than a coincidence that the readings match the label. Are all the rest of the caps I've checked really bad or am I doing something wrong?
 

duke37

Jan 9, 2011
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Capacitors A to E are DC electrolytic capacitors. The meter often uses time to charge to a low voltage. Leakage can affect the results.
Capacitor F is a foil AC capacitor and will not leak in a similar way but may have a high value discharge resistance across it.
 

davenn

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Sep 5, 2009
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Capacitors A to E are DC electrolytic capacitors. The meter often uses time to charge to a low voltage. Leakage can affect the results.
Capacitor F is a foil AC capacitor and will not leak in a similar way but may have a high value discharge resistance across it.

that isn't the main problem

Cap A: 400v 180uF 105c -> .02nF before going to 0L
Cap B: 400v 180uF 105c -> .02nF before going to 0L
Cap C: 35v 1000uF 85c -> .03nF before going to 0L
Cap E: 15v 150uF 85c -> .03nF before going to 0L

these 4 are all too high a value for the meter as according to the manual, the capacitance max is 100 uF
so I'm not surprised you are getting oddball readings


Cap D: 10v 22uF 85c -> 41.75uF

A bit out, but hard to say if it is the meter, or the cap ??
I wouldn't really expect a good 22uF cap to read anything more than around 28uF, taking into account tolerance


Dave
 

73's de Edd

Aug 21, 2015
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Also check a buuuuuunch of other 10 and 22 ufd caps to see if they are testing out OK,
In olden tymes they would always assure that your electrolytic capacitor met the minimum capacitance spec, but some would also give up to a permissible +200% tolerance spec on its high side.

In some past post I told how a person could get a limited range capacitance tester like yours to be able to read on up in the 4700 ufd range, let me see what it was posted within, or I will just retell again.
( LUV dat fast, high flyin' kat !)

73's de Edd
 
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