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Capacitor Testing


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  #21  
Old 08-08-2019, 09:32:33 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Capacitor Testing

So a polarized capacitor is marked as vdc? Non polarized are marked VAC?
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Old 08-09-2019, 11:07:08 AM
Radiomike Radiomike is offline
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Default Re: Capacitor Testing

The capacitors should be marked with the value in µ farads which is 10-6 of one farad. There will be a Voltage rating and this may be AC or DC. Also a manufacturers name and type number. The strategy used for testing will be dependant on the type of capacitor and its value. Electrolytics, much used for filter duty, may require a polarising voltage to establish the insulating oxide layer. This wiki article goes a long way to explaining them https://en.wikipedia.org/wiki/Electr...valent_circuit Electrolytic capacitors will have a quoted ESR and the data sheet will usually give values for the maximum ripple current (usually 120 or 100Hz) in amps. This article deals with testing https://www.testandmeasurementtips.c...ic-capacitors/

Data sheet for typical motor run capacitor, gives typical leakage values as well http://www.bmicaps.com/wp-content/up...runsection.pdf


We need to know the type of capacitor before going further.

Mike
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Old 08-09-2019, 03:45:36 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Capacitor Testing

I believe these are considered aluminum electrolytic capacitors, uf ratings range from 290uf to 53000uf, voltages range from 30vdc to 750vdc, all voltages are listed as vdc. All have screw terminals, diameters range from 1" to 3", height 3" to 9".

There is a pic, but I'm still getting "Internal Server Error" when trying to upload pics
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Old 08-09-2019, 07:56:42 PM
Radiomike Radiomike is offline
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Default Re: Capacitor Testing

These then are electrolytic capacitors that need to be polarised in use. Typically used for filters to remove ripple in rectified DC supplies. The manufacturer will give ESR and ripple current ratings.

If they have been around for a long time and not used they may appear to be short circuit when measures at low voltages, like a DVM or an analogue meter. The answer may be to try reforming them. This recreates the electrolytic action that leads to the insulating film being restored. This article outlines the procedure, but it is just a slowing increasing DC voltage, with a meter and a series resistor to limit current if there is a short. This man has made a smart box to do the job.
https://www.youtube.com/watch?v=fUDB7oavJkg

This is a good summary of what you need to know about electrolytic capacitors.
https://www.tdk-electronics.tdk.com/...nformation.pdf

and a slide show of good information.

https://www.dfrsolutions.com/hubfs/R...Capacitors.pdf

Mike
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Old 08-23-2019, 01:20:13 PM
johndeerefarmer johndeerefarmer is offline
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Default Re: Capacitor Testing

I have used Sencore equipment for years. I have had a LC 103 for probably 30 years. It tests (at rated voltage) value, leakage, dielectric absorption and ESR. Then in about '90 I got a EDS-88A ESR meter that lets me test caps in circuit. This saved me lots of time. It's not for testing motor caps but works great on electrolytics. I have found that on this tester if it's in the bad range it's bad. If it's in the "yellow" range it's still good in most cases. In some circuits higher ESR might not work but in most applications these caps work fine.

I do use my Sencore meter for reforming every electrolytic that I use because I have had them laying around for 35 years.
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Old 08-29-2019, 12:22:34 AM
Zephyr7 Zephyr7 is offline
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Default Re: Capacitor Testing

Quote:
Originally Posted by dalmatiangirl61 View Post
I believe these are considered aluminum electrolytic capacitors, uf ratings range from 290uf to 53000uf, voltages range from 30vdc to 750vdc, all voltages are listed as vdc. All have screw terminals, diameters range from 1" to 3", height 3" to 9".
I’m a little late to this thread.

Nearly all aluminum electrolytics are polarized caps. Screw terminals usually mean you have what are know as “computer grade capacitors”. They generally have high ripple current ratings and usually pretty high capacitance ratings too.

You generally need an LRC (inductance, resistance (fancy resistance though), capacitance) meter. These aren’t usually cheap, but they can measure BIG capacitors as well as TINY resistances. Mine cost me about a grand.

Any big cap will show as a short on a regular multimeter set to resistance or continuity checking mode. It can take a LONG time for the cap to charge enough from the tiny current the meter uses for the test to show as open. It’s better to charge the cap with a battery and measure how much the voltage drops in how much time using a resistor connected across the cap.

Bill
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