Looking for a decent method to test capacitors without a capacitance tester. - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 03:25:42 am
content: Well, I finally got around to looking at the bunch of caps I managed to snag up some time ago (sadly they are smaller than I remembered, and they are all pretty low voltage), I have a feeling they are somewhat old, but maybe they are still good. Unfortunately I don't have a capacitance meter, I do have my UNI-T meter and can hook it up to my computer with the IR connection, so in theory I could stick a load on it, take a bunch of measurements, and hopefully determine the capacity somewhat accurately? Not really sure as I haven't dealt with this before.I do want to pick up one of those cheap capacitance testers, though I don't know if they would work for the capacity some of these have. I know the built in one on my meter probably won't work for crap, but I'm giving it a go as soon as I finish posting this.Here's an album with some images -http://imgur.com/a/407vTI have:2x 5000uf 50vdc (surge 75)14x 5600uf 60vdc (surge 75)6x 180,000uf 75vdc (surge 95)2x 20,00uf 50vdc (surge 65)2x 150,000uf 15vdc (surge 18)Hopefully they are capable of a bit of fun still, I can only imagine what blowing one of these ones would be like, not that I have the gear needed to be able to do that. I think it would be quite the bang.

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 03:33:32 am
content: Actually, it seems like my meter is fairly close, the couple I have tested are a little bit high, but I figured that with the sheer size and capacity of these it would either take ages for it to tell, or it just wouldn't be able to charge them up at all. I always thought the meter would only be good for relatively small capacitors. Cool.

author: bitseeker
author_rank: Super Contributor
timestamp: February 27, 2016, 04:10:31 am
content: Checking the capacitance is a start, but only tells part of the story. Get one of the inexpensive component testers (you can read all about them athttps://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/ ) so that you can also measure the ESR. Even if a capacitor looks like it still has the rated capacitance, if the ESR is high, it won't do you any good.

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 04:15:10 am
content: Quote from: bitseeker on February 27, 2016, 04:10:31 amYeah, that's the main reason I want one of those. A quick charge up did weld a couple alligator clips together and needed a moderate amount of force to discharge them (this was one of the 6 180k uf caps). I just wish I had some bus bar laying around to make an array of these and have some real fun.

author: bitseeker
author_rank: Super Contributor
timestamp: February 27, 2016, 04:25:05 am
content: LOL! Gettin' a little mad scientist, eh? Bzzzzzzt!

author: Addicted2AnalogTek
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:26:42 am
content: You can also measure capacitance and ESR with a scope and function gen. There are multiple ways of doing either.I've noticed it's a bit more tricky to measure the ESR of very large caps that way, though. The way I have had success doing so is by putting a much higher voltage square wave across it and lowering the frequency, which shows the ESR much better.W2AEW has a video on youtube about measuring ESR this way.

author: bitseeker
author_rank: Super Contributor
timestamp: February 27, 2016, 04:31:31 am
content: I totally forgot about using a scope for measuring ESR. Thanks for the reminder, A2AT. Yes, various videos about it on the Tube.

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 04:34:43 am
content: Quote from: bitseeker on February 27, 2016, 04:25:05 amOh, I've done a bit more mad scientist stuff than that, though when I posted it here a couple members decided to ream me out pretty badly. (using some bridge rectifiers to charge high voltage caps, since I had no other methods). Now I have an electrophoresis power supply, that can provide a pretty wide range of voltages, though not very stable for some reason, tried to fix it but couldn't get it perfect (https://www.eevblog.com/forum/repair/250v-electrophoresis-power-supply-troubleshooting-very-unstable-output/10/?wap2), so that should work to charge them up.That thing also fries resistors ridiculously well, I wish I had a high speed camera, they are like fireworks :pQuote from: Addicted2AnalogTek on February 27, 2016, 04:26:42 amThat sounds even more out of my budget lol Plus this is just tinkering as I've been stuck inside for a week with a nasty ass cold, and I'm feeling the urge to actually do something. Spent a few days of that with maybe 3-4 hours awake tops, and not all at once.

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 04:37:18 am
content: Ah damn, just grabbed that power supply and was reminded why I haven't used it in a while, somehow the fuse holder popped out, and I don't have any extra ones laying around lol.

author: XOIIO
author_rank: Super Contributor
timestamp: February 27, 2016, 05:38:52 am
content: Just remembered I had these for a proper mad science project, I want to make a dual channel tesla speaker system with then, if these little ones can pump out enough voltage. Always been in love with tesla speakers but never gotten around to making one sadly.

author: dexters_lab
author_rank: Unknown
timestamp: February 27, 2016, 11:09:08 am
content: Quote from: XOIIO on February 27, 2016, 03:25:42 amyea, i've done this by charging caps up through a resistor and working out the time constantyou can also measure ESR with a scope and function generator as per w2aew's video:be gentle on old electrolytics if they have been left uncharged for a long period:http://dexterslab2013.blogspot.co.uk/2015/12/reforming-electrolytic-capacitors.html