Capacitors

The problem is that usually the capacitors you want to test are installed in malfunctioning or nonfunctioning piece of equipment.

As such, the capacitors in question are typically not isolated, so using a multimeter or wheatstone bridge won't help.

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There is a reliable method for diagnosing a bad capacitor in malfunctioning electronics. Answer the following questions:

1. Is the malfunctioning device free of things like signs of arcing (mostly on circuit boards), blown fuses, dead batteries, absent power supply, evidence of blunt force trauma, and/or dripping water?

2. Does the device have one or more electrolytic capacitors?

Yes to both? Currently have a Bad Capacitor. Look for swelling.

Yes to #2? Bad capacitor... if not now, eventually.

thanks guys, both ga's from me.

to find the capacitor is good or bad, simply put the capacitor probes into the socket and switch it on for 1sec and after that remove the probes from socket and try to touch one probe with other probe, on touching it generates some spark ( discharging the charged current). If it is not generated any spark then it is a bad capacitor other wise it is good capacitor

This can work in some cases but it would be much better to use a multimeter set to voltage setting to see if the capacitor is holding a charge (provided by a battery or similar extra-low voltage DC source).

Surely you have access to a multimeter durtieduck .

yes, ihave a multimeter, but i was'nt sure how to charge the cap without using high voltage.

You can still use extra-low voltage (for example 12V DC).

The results are less accurate if it is a high voltage low capacitance capacitor but will still give you a good (and safe) indication.

When you say high voltage I'm thinking you want to check a start or run cap. You can use your ohm meter. The leads from the meter will charge the capacitor. Start at the 1k setting. Read the meter will show low numbers to higher numbers until the capacitor reaches saturation then the numbers will drop to 0. Then reverse the leads and check again. If its leaking the numbers will go up but won't return. Open will read infinity. Shorted will read 000. If the capacitor has a resistor across it you will have to disconnect it first or you will be reading the resistor. Remember what Mike said always short the cap in question across the terminals with a well insulated screwdriver for safety sake. Hope that helps.

If this capacitor has terminals for quick disconnect, it's fairly easy. First short out the cap with a load resistor, a nice big one, don't hold it in your hand, it'll get hot.

If you don't have a resistor, short it out with metal, but be careful, some caps can hold quite a wallop.

Once discharged (which usually means the cap is good) take an ohm meter and check for resistance. The meter should jump, and then settle down to no reading. Then reverse the leads...the meter should jump the same amount again, and settle down. This shows a good cap, usually.

If the cap is soldered onto a board, you usually have to remove it for testing. The same test applies. Be careful un-soldering it, discharge it first. Like mentioned, a swollen cap is bad, the little cover on the top bulges at the score marks.

If you're going to be fussing with electronics, get a cap tester, and an ESR tester.

Sorry Mike. I didn't mean to rain on your parade. I didn't read all the comments before answering. It is consoling to know that we are on the same page.

No problem, happens all the time. I'm sure I do it, too.

this may seem a bit off subject, but does anyone remember charging a car ignition cap from a spark plug wire, then tossing it to some innocent soul to catch it?

Electrolytic capacitors nearly always fail open. So a quick check is to parallel another capacitor that has the capacitance that the failed capacitor had.

Of course this doesn't work for other type capacitors. Don't know if it works for tantalum capacitors or not.