Can I check electrolytic caps?

[tpatton]

I've taken 15 electrolytic caps out of a hopelessly broken-down CD player.  These are upgrade caps I put in myself, and I blush to admit that once again (last time with my SEX amp) I put one in with reversed polarity.  It heated up and started to bulge.  What I'm wondering is whether it took other caps with it.  It does seem to have destroyed a regulator, which heats excessively even with the wrong-polarity cap replaced by the original one that it replaced.  That CD player is, for other reasons, a dead loss, and I've now removed all 14 right-polarity upgrade caps.  Is there any way I can tell if they're still okay?  I've tried resistance measurements across their pins, with no hope of learning anything, just giving it a try.  But I have an ancient Heathkit sine/square wave generator that still seems to work.  Is there any way I can use it to test these possibly compromised upgrade caps?  Again, they're now out of the CD player, which is itself in a closet, maybe good for spare parts, especially its drawer/laser assembly, which has been declared by an expert to be in good shape.  Thanks in advance for any advice.

[Laudanum]

Wouldnt capacitance measurement be a good start?   Im suggesting but morseo asking for a chance to learn something.

[cvandyke]

Having repeatedly faced the question of whether an electrolytic capacitor is still good, I eventually bought an ESR meter which is designed to answer this question. Not particularly cheap and definitely a specialty tool, I've found it very worthwhile because I sometimes repair old equipment or salvage electrolytics. The ESR meter measures the equivalent series resistance of a capacitor by applying a high frequency, low level AC signal. If the capacitor is bad, this ESR will rise. The best part is you do not need to remove the capacitor from the circuit to test it.

A good introduction is at this link which also contains a schematic if you want to DIY: http://ludens.cl/Electron/esr/esr.html

I bought a kit that cost $85 and was easy to assemble (can also be bought assembled). When I was looking into this years ago, I found a number of kits and assembled meters and I don't really remember why I selected the one I did. I suspect it was one of the cheaper ones available since I'm frugal (e.g. "salvage electyrolytics"). Here's a link to the one I purchased: http://preher-tech.com/esr.aspx

[tpatton]

My Fluke multimeter measures capacitance only up to 47 uF, in answer to the first reply.  As to the second, thanks for the Praher-Tech suggestion, but to be even more frugal, might this one be any good?

http://www.ebay.com/itm/VC6013-digital-capacitor-capacitance-meter-200pf-to-20mF-discharge-/290631312490?pt=BI_Electrical_Equipment_Tools&hash=item43aaf9e46a#ht_5424wt_952

I'll wait to hear before doing anything drastic.  Thanks again.

[Grainger49]

I have seen some damaged electrolytic caps.  If either the bottom or top, the two circular ends, are bowed rather than flat the capacitor is damaged. 

I should have kept one of those I removed from a still dead PS Audio P500 I own.  I did post a picture of a dead Oiler here:

Spotting A Bad Oiler Or Electrolytic

[ironbut]

That 'Blue' ESR meter looks like a great deal and I like the idea that it's a kit.
Unfortunately, about a year ago I gathered the parts for another DIY meter. Worse yet, all the parts are still in a labeled box and is waaaay back in the project queue.

http://members.shaw.ca/swstuff/esrmeter.html

[cvandyke]

"My Fluke multimeter measures capacitance only up to 47 uF, in answer to the first reply.  As to the second, thanks for the Praher-Tech suggestion, but to be even more frugal, might this one be any good?"

I don't think measuring the capacitance will really tell you if an electrolytic is healthy so I wouldn't get that inexpensive meter if that is your reason for buying it. According to an old Sencore information sheet for the LC53 meter, "less than 25% of capacitor defects cause a change of value." Of course, this is effectively an advertisement so who knows if this is true; it doesn't seem unreasonable from my experience.

I own both a handheld LCR meter (Extech 380193) and an expensive benchtop LC meter (Sencore LC53) and both will measure capacitance even on an electrolytic that is going bad. The LCR meter is useful for quick measurements and can tell you if a capacitor is completely dead but it's not very accurate . I actually use the cheap meter more which is mostly a matter of convenience but if I want to accurately measure capacitance or do a leakage test, I use the Sencore. If I want to know whether an electrolytic is OK, I use the ESR meter preferentially. It's easy and gives an fast "go" or "no go" answer.

[tpatton]

I asked, in my first post, whether my old Heathkit Sine/Square wave generator could be used.  Here might be a Ludens passage to note:

The design presented here works by applying a 50kHz, 200mV square wave to the capacitor under test, in series with a 10 Ohm resistor. The AC voltage appearing across that resistor is measured and displayed on a meter. So the whole thing is nothing else than a simple ohmmeter that uses ultrasonic AC for measurement instead of the usual DC used by every common ohmmeter.

I can't see why I couldn't manage that, though making it convenient might be a challenge: getting the 10 ohm resistor in series with one of the cap's leads--should it be the negative?  I'll work on that.  Can anyone assure me that it should work?  I can measure AC voltage.

Thanks for any ideas/confirmation on this.

[Grainger49]

The 10 ohm will form a high pass filter at 1/2*Pi*R(10 ohms)*C.  I think that might work.

[2wo]

How about applying the expected DC voltage to them. If they are OK they will just sit there, if not they will get hot, maybe pop. Cover it with an old tumbler or jar...John   

[Paul Birkeland]

I would apply the rated DC voltage through a 10k resistor in series with the capacitor.  Of interest is the DC voltage across that 10k resistor.  It should ramp up, then steadily decrease to zero as the capacitor charges up. 

If the voltage doesn't drop to zero, then you can throw the cap away (note - this necessitates not having a bleeder on the cap).

[ironbut]

Nice tip Paul!
Thanks.

[tpatton]

My signal generator does square waves or sin waves, and unless I'm missing something, is not a source of DC voltage.  Hopeless?

[Paul Birkeland]

My signal generator does square waves or sin waves, and unless I'm missing something, is not a source of DC voltage.  Hopeless?

You can rectify the sin or square waves to get some DC.