19-yr old 250v Cornell-Dublier Electrolytic caps - still trustable? - Page 1
Forum section: electronics / beginners

author: Cliff Matthews
author_rank: Unknown
timestamp: May 19, 2015, 02:13:09 am
content: Lately I got some work shutting down and scrapping some big tri-phase inverters. Amongst the gems, were 18 x 9,100uf 250v caps, similar Spragues, some HiCon 6,800uf 250v, and some 6 other 2,100uf 400v Nippon Chemi-con's. Yesterday, I charged them all for about 20 seconds to 180 volts and today, most are still above 100vThey were just pulled from working equipment, but will my shelving them cause them harm? Should I be hurried to put them to other use?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 19, 2015, 10:53:48 am
content: At worst, they might need to be reformed (charged slowly up to rated voltage with a limited current). If they were in continuous or infrequent use until recently, they're probably perfectly fine.ESR might go up if they dry out, but if they weren't heavily used, that should be fine as well.You might not be able to measure the ESR because it will be fairly low for capacitors of that size.Tim

author: rsjsouza
author_rank: Super Contributor
timestamp: May 19, 2015, 11:25:31 am
content: As said by T3sl4co1l, they are probably fine if they were not exposed to extended use or extreme conditions (temperature, humidity, etc.)A good thread that discusses older capacitors and reforming ishere

author: macboy
author_rank: Super Contributor
timestamp: May 19, 2015, 01:05:09 pm
content: I would not hesitate to use those caps. I might be tempted to reform them first.I would, however, have reservations about putting 180 VDC, from a capacitor capable of delivering immense current, across that $5 multimeter.

author: Cliff Matthews
author_rank: Unknown
timestamp: May 19, 2015, 01:13:42 pm
content: Thanks rsjsouza, nice thread indeed! Although Dexter's Lab YT channel diverted me for a while..I'm planning to use two of the caps on the far left to view inductor saturation traces.Macboy, yes they were 5.99 a few months ago I believe.. but your point is well taken. I got three of those from crappy-tire to use as my shop floaters. But then again, what could happen in one milli-second?

author: eas
author_rank: Frequent Contributor
timestamp: May 21, 2015, 09:42:11 pm
content: Quote from: Cliff Matthews on May 19, 2015, 01:13:42 pmWell...

author: Cliff Matthews
author_rank: Unknown
timestamp: May 28, 2015, 07:45:59 pm
content: FWIW, 12 days past since charging all to 180v and out of 24, only 2 self-discharged within ~3 days. The others still measured between 20 and 40 volts before I discharged them with a 4.7k resistor.An odd observation:All were rated 250v except the 4 smaller (2100uF/400v Nippon Chemi-Con's) on the right - It is these, despite being of smaller capacitance, that retained the highest charge. Is this brand just better? or was it the dielectric?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 28, 2015, 11:33:15 pm
content: If you didn't reform them (idle up to rated voltage with a limited current supply), the leakage can be expected to be very large, especially at voltages near the rating (and proportional to it).One would suppose the 400V caps are in a "formed" state such that their leakage at equal voltages (and therefore smaller V / Vmax) is lower.Value doesn't matter; self discharge is essentially a time constant. Obviously, bigger caps have more potentially-leaky area, and higher voltage caps have thicker area.Tim