So much for ESR meters. - Page 1
Forum section: electronics / general

author: G7PSK
author_rank: Super Contributor
timestamp: February 28, 2013, 04:46:47 pm
content: I was adjusting a DC to DC converter when a horrible odour arose and the end of a capacitor started to bulge before my eyes.I removed the offending item from the board to replace it.I checked the replacement capacitor with my ESR meter before fitting it and got the reading of 979.3 uF and 0.11 ESR for what a capacitor rated at 1000uF 35V. out of curiosity I checked the blown capacitor and got the reading of 807uF and 0.08 ESR.How can this cap still appear good when the circuit it is in will not work but does with the replacement and if looking for a fault one would get a reading indicating a good capacitor.

author: w2aew
author_rank: Super Contributor
timestamp: February 28, 2013, 05:02:34 pm
content: Did you check it for leakage at the rated voltage?Also, I have seen some cheap capacitors that were improperly packaged, with the polarity backwards! They don't last long...

author: mzzj
author_rank: Super Contributor
timestamp: February 28, 2013, 05:59:50 pm
content: Quote from: w2aew on February 28, 2013, 05:02:34 pmToday's crappy (mostly water based) electrolyte will show up first as a increased leakage current and only a lot later as ESR increase.Leakage current is often sign of electrolysis going on inside your capacitor and thus gas buildup. Next You have bulged cap...

author: G7PSK
author_rank: Super Contributor
timestamp: February 28, 2013, 06:12:17 pm
content: Quote from: mzzj on February 28, 2013, 05:59:50 pmSo if there is no obvious bulging or leakage the ESR meter may well not pick up the problem when looking for a problem in a circuit. So what good are they then if you suspect capacitor problems, all you can do is change them all out until the problem goes away, as the ESR meter will not show the faulty item as they do not supply enough voltage during testing.

author: kripton2035
author_rank: Super Contributor
timestamp: February 28, 2013, 06:23:57 pm
content: almost same problem here : I changed some 20 capacitors on a motherboard to check them they are all within spec for capacity and esrbut they simply dont work. will try to make a leakage test device to check them better.this one is a good candidate :http://kripton2035.free.fr/digital%20esr/esr-sprut-de.html

author: w2aew
author_rank: Super Contributor
timestamp: February 28, 2013, 06:50:32 pm
content: Quote from: G7PSK on February 28, 2013, 06:12:17 pmA leakage tester, using a simple power supply and one of Dave's uCurrent devices would be a decent way go.

author: mzzj
author_rank: Super Contributor
timestamp: February 28, 2013, 07:02:52 pm
content: Quote from: w2aew on February 28, 2013, 06:50:32 pmNo need for Dave hereYou can as well just use shunt resistor and measure voltage over it. 1k resistor gives you 1mV per 1uA. Burden voltage is not much of a problem since you got plenty of voltage.For low voltage caps I use HP 6632B power supply since it can measure down to 1uA

author: Unknown
author_rank: Unknown
timestamp: February 28, 2013, 09:44:45 pm
content: You may have an AC ripple problem...That's to say, the Cap rating is incapable of taking say 100mV ripple or less.