Electrolytic Cap Replacement - Page 1
Forum section: electronics / beginners

author: b9creations
author_rank: Contributor
timestamp: April 20, 2015, 09:22:39 pm
content: Hello, Greetings Dave love your youtube stuff, can't stop watching! LOVE IT!I am re-creating a circuit board from the 80's and wondering about the 2ea 22uF 250V Electrolytic caps.Thinking about possibly replacing the current ones with 8000 hour lone life rated models, but confused about how to go about that, or if it's possible?This looks like an exact match: Expensive things in exact vintage form!http://www.ebay.com/itm/1pcs-BC-PHILIPS-118-AHT-22uF-200V-125-C-250V-85-C-Axial-Capacitor-12-5x30mm-/151284364560?pt=LH_DefaultDomain_0&hash=item2339403510And here is the data sheet for the current model:http://www.vishay.com/docs/28334/118aht.pdfAnyone know how to figure out a suitable replacement that will work reliably, or should I just stick with the modern equivalent which seems to be this part?http://www.mouser.com/ProductDetail/Vishay/MAL211892229E3/?qs=%2fha2pyFaduhI6g1igiRtPZqnQBOYbfWfTa5vM2IWXpfiBZjQx2wuLg%3d%3dAlso, the vintage originals say 250V but the modern day equivalent seem to be rated @ 200V.Thanks for the help, I am a newbie of course.Best, B9C

author: b9creations
author_rank: Contributor
timestamp: April 20, 2015, 10:39:26 pm
content: Ok, maybe I should rephrase the question:How important are ripple current and ESR and impedance ratings? Should they be the same can they be a bit higher/lower?This seems to be a possible replacement 250MA ripple 250V VS 225MA ripple but can's seem to find ESR or impedance rating anywhere:http://www.digikey.com/product-detail/en/UCY2E220MPD/UCY2E220MPD-ND/2597724Original cap is rated at ) 3.17 Ohm ESR and impedance of 2.22 Ohm. Hmmm..Perhaps for ultimate reliability I shroud stick with modernized identical original? @ 2.90 each from mouser vs .90 cents? Big difference if I make several of these boards.I also wonder if there may be suitable SMD equivalent? I can't seem to find anything. Will keep searching.Thanks for any possible comments!Best, B9C

author: mariush
author_rank: Super Contributor
timestamp: April 20, 2015, 11:27:43 pm
content: In general, ESR should be as close as possible or lower than original capacitor's value.Ripple value should be as close as possible or higher than original value.In your particular case, the board being so old it would also have capacitors with plain average specifications. Nowadays, even general purpose, cheapest series of capacitors would probably meet or exceed the specs of those old capacitors you have on the board.ESR probably matters less with the circuit you have, it's more critical with switching power supplies and similar circuits.You shouldn't look in online stores for the best spec capacitors, aim for something close to the specs of those old ones.For that 22uF 250v capacitor, it would also be safe to go with capacitors that are rated for higher voltage like 400v or 420v. You should keep capacitance the same.

author: b9creations
author_rank: Contributor
timestamp: April 21, 2015, 06:42:25 am
content: Excellent, thank you Mariush, that's exactly what I needed to know.I do have one more question: If the ESR is not listed in the data sheet, is there some way to calculate it from some other commonly listed data? I will look again, maybe it's there and I am just not seeing it.Some of the vendors list it in the description, but apparently not in all cases. So I guess it depends on the manufacturer.And since ESR is in ohms is there a simple way to test it with a multimeter or digital scope?Many thanks B9C

author: mariush
author_rank: Super Contributor
timestamp: April 21, 2015, 09:35:51 am
content: For capacitors used in switching power supplies (pc power supplies, monitors, tvs etc), where the circuits work at high frequencies (60kHz and up usually), the ESR value of a capacitor is very close (almost the same) to the Impedance value specified in the datasheets (the one listed at 100 kHz), so generally that's what the measurement is compared to when checking a capacitor's "health"You measure ESR with an LCR meter (that has ESR measurement function) or cheap ESR meters you can find on eBay.The cheap ESR meters don't really measure the ESR but something very close to the actual ESR, and for what they're used (checking if a capacitor is bad or close to specs) they calculate a good enough/close enough value to be worth the money.Note that there are actually some "professionally" made meters that only do capacitance and esr like the atlas meter shown below but these are exceptions.An LCR meter with ESR measurement can be bought starting from around probably $80-90, cheap esr meters can be found with prices from about $15-20.It is possible to measure the ESR with an oscilloscope but it's cumbersome and you'd need additional components to make a small circuit in which you'd "plug" the capacitor under test, see first video below if you want to learn.

author: b9creations
author_rank: Contributor
timestamp: April 21, 2015, 06:34:52 pm
content: Excellent, got it. Thanks for posting all the vid's, greatly appreciated!Best regards, smiles, B9C