Capacitor Checking, Electrical

Old 06-16-04, 04:32 AM
John A. Kelley
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Capacitor Checking, Electrical

What are the specific steps that should be followed to test an electrical capacitor to see if it is good or if it needs to be replaced?
Old 06-16-04, 06:57 AM
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Well, its usually cost prohibitive to test a capacitor. Most people replace them if they are suspect, and if it doesn't solve the problem, move on to something else. Unless you are talking about a very large/expensive one.
The more expensive multimeters sometimes have Capacitance settings.

If its a very large one, you you could connect it accross a known DC voltage source (maybe 6-12 volts) and then disconnect the source and use the voltage setting of a multimeter to see if the voltage slowly lowers.

What kind of circuit is this capacitor located on?
Old 06-16-04, 08:00 AM
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Look out when you do it but. Pull the cap out, put power to it.Take the power off of it and short it out with a good insulated screw driver,should get a good blue spark. Now if a start cap and it has a resistor on it you have to take it off the cap on one end to do this. AS I SAID LOOK OUT WHEN YOU DO THIS

Old 06-16-04, 10:57 AM
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John A. Kelley,

Another way is close to what Ed suggests but you could also apply power and measure the amperage.

Not as accurate is to use an analog ohmmeter.
Remove the capacitor, short the terminals with an insulated screwdriver to remove any residual charge and cut one side of the resistor if there is one.
The range setting on the ohmmeter will depend on the mfd and voltage rating of the cap but I would start on X1 and work down from there.
While watching the needle apply the probes to the terminals and if the capacitor is close to being ok the needle will rise as it accepts a charge and then immediately fall once charged.
If the needle doesn't move then raise the range, short the terminals and then try it again.
Can't get the mf rating this way but it is a reasonable go/no go test.

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