What sort of capacitors are these? - Page 1
Forum section: electronics / repair

author: motocoder
author_rank: Unknown
timestamp: October 16, 2014, 04:43:41 am
content: I'm doing some work on a very old Power Designs precision power supply. Among other things, I've been replacing the electrolytic capacitors. However, there are a couple of capacitor types I see in there an for which I am not sure what type they are, and whether they are the kind that degrades over time and may be in need of replacement.The first type is the large green capacitor in the first picture below. The "+" and "-" on top (partially visible) were drawn by me with a marker, based on the polarity of the voltage across the cap. So don't see those and assume it's polarized; it may or may not be.The second type of capacitor is the orange cap visible in all of the pictures. I can't see any clear polarity marking on these either, so I wasn't sure.Thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 16, 2014, 06:31:03 am
content: Probably both film, I've seen those Spragues before but not sure what's inside them really. The metal case suggests electrolytic, but not the value/rating. Any other numbers on them?If they're film, I'd be very surprised they're showing problems.Tim

author: Kjelt
author_rank: Super Contributor
timestamp: October 16, 2014, 07:08:27 am
content: Quote from: motocoder on October 16, 2014, 04:43:41 amThis might be a bipolar electrolytic capacitor, not sure though.

author: motocoder
author_rank: Unknown
timestamp: October 16, 2014, 08:00:42 am
content: Thanks for the replies, folks. I ended up blowing that power supply up,this evening, so no point in checking these caps.

author: David Hess
author_rank: Super Contributor
timestamp: October 17, 2014, 06:16:37 am
content: They are Sprague 192P series polyester (Mylar) film/foil capacitors making them larger than metalized film capacitors.http://www.symmetron.ru/datasheet/vishay/passive/42024/192p.pdfI have a parts drawer full of them.

author: motocoder
author_rank: Unknown
timestamp: October 17, 2014, 11:53:59 am
content: Quote from: David Hess on October 17, 2014, 06:16:37 amThanks, David. Good to know they are non-polarized, and maybe the info will come in handy on a future Power Designs repair.

author: David Hess
author_rank: Super Contributor
timestamp: October 17, 2014, 01:30:22 pm
content: Quote from: motocoder on October 17, 2014, 11:53:59 amAs a practical manner, any C0G/NP0 ceramic capacitor or film capacitor should work to replace it but they may have used a film/foil capacitor for lower ESR or ESL or because metalized film capacitors are sometimes noisy because of the way they clear shorts.Based on the location, I think they wanted low ESR and/or ESL.I have never encountered a bad Sprague 192P series capacitor.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 17, 2014, 10:03:46 pm
content: Seems more likely they simply didn't need or want something cheap, like metallized film. Or it wasn't even available (when was metallized film introduced?). Or, they'd just been using the Spragues for literally the last 30 years, and had no reason to change as they were still available.715P ("orange drops") are still chosen today for much the same reason, except the time frame is even longer. They're actually quite good at RMS current / pulse, though this aspect is not well rated IIRC, and the people who pick them rarely understand the appropriateness of that choice for their application (e.g., recapping tube amps -- freaking coupling caps don't take any current at all, and the cheapest polyester is more than sufficient there).Tim

author: David Hess
author_rank: Super Contributor
timestamp: October 18, 2014, 02:51:03 pm
content: Quote from: T3sl4co1l on October 17, 2014, 10:03:46 pmI am not old enough to remember a time when film/foil capacitors were available and metalized film capacitors were not. Metalized capacitors are less expensive, smaller, and more reliable if not as rugged. Film/foil capacitors have a lower ESR and may be quieter; that could be enough to not replace them in some applications. In this case they are being used for very low ESR decoupling.Vishay must have discontinued the 192P series after acquiring Sprague. I could find neither them nor a replacement for them them on their web site but there is a Vishay labeled datasheet for them.QuoteI just use whatever film capacitor is convenient but not polystyrene if tubes are around because of temperature. The original paper/oil capacitors are so poor that any film capacitor is an improvement unless the non-ideal qualities of paper are desired or there are noise issues with metalized film from self healing.I still need to finish replacing the paper/oil capacitors in my ESI impedance bridges.