Cap testing - Page 1
Forum section: electronics / projects

author: boston617
author_rank: Newbie
timestamp: January 30, 2016, 05:16:36 am
content: I've got a Nippon Chemi-con CE02W SM 2400uf 25v, test showing 2765uf and testing ohm range shows not shorted (OL on display). Sadly I don't have an ESR meter (yet) so I can't test that. I'm not sure if I'm within spec or if the cap has gone and needs to be replaced. Was in a audio power supply filter that I was checking due to HF noise. Searching online has got me nowhere yet.

author: CaveMannDave
author_rank: Regular Contributor
timestamp: January 30, 2016, 08:03:12 am
content: Hi:25+ years ago, when I first butted-heads with ESR, (WAY before it had become common knowledge outside of the cap 'industry', before there was any affordable tester) I found that standard (ie, not switchers) power supplies of malfunctioning equipment would show LARGE AC voltage across the terminals of filter caps, I mean, several volts on a +/- 12 volts rail PID temperature controller.Look at the ripple, under load, at 1x and 2x the rectifier frequency, IGNORE really HF crap and noise (those probably are riding-in on wiring, or coming backwards from later stages), and try to correlate the noise with it's origin.HTHCheers,Dave

author: halexa
author_rank: Regular Contributor
timestamp: January 30, 2016, 06:46:31 pm
content: Hi,If you have a function generator and a oscilloscope you can easily check the ESR of a cap:

author: uncle_bob
author_rank: Unknown
timestamp: January 30, 2016, 10:45:39 pm
content: Quote from: boston617 on January 30, 2016, 05:16:36 amHiIf by HF you mean it in normal "RF" terms (above 2 MHz) then the cap you have is going to make zero difference. Electrolytic caps have turned into open circuits long before then. If an electrolytic still shows low impedance by the top end of audio, it is doing *very* well. The physics of the part makes this be so.If by HF you mean "high audio" then *maybe* but still not likely. If the part is in the power supply, it's dealing with rectified AC mains voltage. There's not a lot that can go wrong in that process that would normally be described as high audio noise. When one goes out, what you get is low end audio hum.As noted in another reply, a quick check with a scope while the gear is running will show you the ripple while it's under it's normal load. That will give you a good idea if it is doing the right job or not.Best guess (and its only a guess): The cap is fine and your problem is somewhere else in the equipment.Bob

author: boston617
author_rank: Newbie
timestamp: January 31, 2016, 02:42:35 am
content: Quote from: CaveMannDave on January 30, 2016, 08:03:12 amQuote from: uncle_bob on January 30, 2016, 10:45:39 pmThe supply seems to have other issues going on. The only thing that seemed out (at the time) was the cap reading 300+uf higher than the marked rating. I'm replacing the supply tomorrow with another that should do.

author: uncle_bob
author_rank: Unknown
timestamp: January 31, 2016, 02:46:52 am
content: HiYou have to consider the tolerance most electrolytic caps are made to. Things like GMV (guaranteed minimum value), -20% +80% and the like show up on electrolytic cap data sheets (occasionally on bypass cap data sheets as well). If anything, the cap being "over value" is a good thing. More C makes the supply work better. Less C gives you more ripple and can cause trouble.I'd suggest you keep digging into the supply.Bob