Inexpensive Capacitor Leakage Tester - Page 1
Forum section: electronics / beginners

author: jsi
author_rank: Regular Contributor
timestamp: February 19, 2018, 02:33:26 am
content: I've got a tube radio and a tube organ from the early 60's that I would like to make usable again. There are ample warnings on the net about how pretty much all old capacitors leak and need to be replaced. So I hacked together a capacitor leakage tester with my DC power supply and an old Simpson Model 374 microamperes meter. My power supply maxes out at 64 volts so I started testing some of the 100 volt capacitors in the parts bin. I was surprised how many of new, never used capacitors leaked DC current.Which brings me to the 600 volt capacitors in these tube devices. To test them I'm going to need more that 64 volts and that gets expensive fast! Heathkit IT-11 or IT-28 testers go for a small fortune and high voltage bench top power supplies are in the thousands of dollars. I want to test the replacement capacitors before I install them because these old guys were NOT designed with ease of repair in mind.Any ideas on how to test these high voltage capacitors without spending a fortune?

author: ogden
author_rank: Super Contributor
timestamp: February 19, 2018, 02:50:45 am
content: I don't see reason why you would want to check specs of modern, band-new capacitors of reputable manufacturer which obviously you shall pick.

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 19, 2018, 03:48:32 am
content: Quote from: ogden on February 19, 2018, 02:50:45 amThey have infant mortality and can fail new. It's extremely rare though for good brand caps (I've seen it happen on Youtube though). For cheap caps, I'm not sure (just avoid them).

author: bitseeker
author_rank: Super Contributor
timestamp: February 19, 2018, 07:01:45 am
content: Nice ammeter, jsi. Be sure to bring caps up to voltage slowly to minimize the risk of pegging the meter.If you want to get an actual leakage tester, don't limit yourself to the Heathkit ones. Many Heathkit devices go for too much money on eBay. It's also a good idea to get one that discharges the cap, either automatically or with a button/lever, prior to removal.Be sure to check local sources, too. I got a Sprague TO-6 locally for significantly less than they go for on eBay.If you're comfortable with high voltages (I assume so, since you're going to work on tube stuff), you could make your own tester. Have a look at the schematics in the operating/service manuals for some of the vintage testers.

author: Damianos
author_rank: Frequent Contributor
timestamp: February 19, 2018, 10:42:56 am
content: Quote from: jsi on February 19, 2018, 02:33:26 amElectrolytic capacitors need some time to operate in specifications. In the datasheets, leakage current is specified, but also an initial time period to achieve this. So, when testing electrolytic capacitors, give them some time to reconstruct the insulating layer.QuoteFor testing capacitors a low power voltage source is enough.Because a small high voltage transformer may be difficult to find, a voltage multiplier seems more convenient. Using a selector switch gives voltage steps/ranges.Another solution is to use a low power boost converter.

author: danadak
author_rank: Super Contributor
timestamp: February 19, 2018, 11:24:34 am
content: Some useful stuff including known manufacturers and types thatwere and are issues -https://antiqueradio.org/recap.htmhttps://www.radiomuseum.org/forum/replacing_old_capacitors.htmlhttp://www.antiqueradios.com/forums/viewtopic.php?t=91359&view=previoushttps://en.wikipedia.org/wiki/Capacitor_plaguehttps://mailman.listserve.com/pipermail/collins/2010-December/msg00031.htmlhttp://www.eham.net/ehamforum/smf/index.php?topic=3785.0;wap2Regards, Dana.

author: Shock
author_rank: Super Contributor
timestamp: February 19, 2018, 02:21:20 pm
content: https://www.eevblog.com/forum/repair/capacitor-leakage-tester-checker/

author: Old Printer
author_rank: Frequent Contributor
timestamp: February 19, 2018, 03:45:20 pm
content: I have a couple Fender tube amps from about 1972 so this interests me. Are you considering replace original caps with new old stock and therefore want to test them? I know good quality large caps can be expensive, but for the work involved that would all I would consider using and would trust the mfgs QC. I would be interested to learn if that is a naive thing to do.

author: jsi
author_rank: Regular Contributor
timestamp: February 19, 2018, 05:30:39 pm
content: Quote from: Old Printer on February 19, 2018, 03:45:20 pmI bought the replacement caps from justradios.com He's got just about everything you could want for these old tube amps. I never considered putting new old stock (NOS) in my projects. Lots of stories about them being bad too. The explanation that seemed to make the best sense to me was it's like replacing the tires on a classic car. Nobody wants to drive around on leaky old tires, and the same thing goes for old capacitors. YMMV, but IMO a cool working radio is far more fun than a pretty box that doesn't do anything.

author: jsi
author_rank: Regular Contributor
timestamp: February 20, 2018, 12:38:57 am
content: Quote from: bitseeker on February 19, 2018, 07:01:45 amGreat! The Sprague TO-6 is officially on the hunt list.My wife loves to hang out at estate sales and she always calls me when she comes across any electric stuff. The Simpson ammeter is an example of such a find.The idea of making a tester has crossed my mind. But, as I think this through, buying a used meter might be the best way to go. I've got 2 projects: a radio / record player from my youth, and a Hammond Organ from my wife's childhood. After that I'm going to be done with this old stuff. I much prefer working in the digital realm. If I pickup a used Heathkit or Sprague tester I can resell it when I'm done. I've done that with other tools that were needed for a project and in the end they cost me next to nothing.

author: Old Printer
author_rank: Frequent Contributor
timestamp: February 20, 2018, 01:46:30 pm
content: Quote from: jsi on February 19, 2018, 05:30:39 pmWhat I meant is I would trust QC on good brand caps from current manufacture (i.e. Sprague from DigiKey). NOS maybe fine for tubes, but old caps are old caps, in circuit or in the bag.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2018, 01:56:28 pm
content: It's easy to measure the leakage of a capacitor, with a multimeter and stopwatch.Charge the capacitor, to the appropriate voltage.Leave it to stand, with nothing connected to the terminals, for a known amount of time.Set the multimeter to read the maximum voltage, connect it to the capacitor and record the reading.Calculate the lost charge and work out the equivalent parallel resistance/leakage current.

author: jsi
author_rank: Regular Contributor
timestamp: February 20, 2018, 05:25:39 pm
content: Quote from: Hero999 on February 20, 2018, 01:56:28 pmThe procedure you describe sounds like a discharge test which in my learner's mind is different than a leakage test. I need to test for DC leakage through the capacitor. I'll leave the distinction between the two for the more experienced people here.What I'm going to do is haunt ebay and Craigslist untill I find a suitable tester. I'll buy it, use it for two projects and then sell it. If I pay the right price to start with, I'll be able to sell it for what I paid. So, when all is said and done the tester is free.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 20, 2018, 07:01:06 pm
content: http://www.pa4tim.nl/?p=1385my page about reforming and leakage measurement. At the end of the page some simple schematics from the ones I builded and use (a lot)There are two different leakage principles. The first one is stated in the manual from the electrolytic caps. Stated for 1 and/or 3 minutes. I have never done those tests so I do not know the right set up for that. I have a WK bridge that has a leakage function but the manual does not explain how to interpret the result and do the test. It is done with a low voltage. I think it is some kind of coulomb measurement. After one minute the cap must be charged to the max voltage (3V ? ) from the tester. The charging current then will be zero. If not it is leaking. This is a test for normal formed caps.This is not the leakage you worry about in old tube gear that is long not used. That has to do with the leakage of the degraded oxidelayer on the working voltage. So a "defect" but often "repairable" You test that at the working voltage so you know for sure the oxide layer can withstand that. Just for safety. This way you can find defects in the isolation. If have seen caps working perfect at some voltage (far beneath the working voltage) but if you increase the voltage, nothing happens other them more leakage current. Almost like it is a zener. (until it heats up to much and then poefffff )

author: daedalux
author_rank: Contributor
timestamp: February 20, 2018, 09:34:22 pm
content: Use a regular 250V 500V 1000V insulation tester in the range it fits. Have one, is very useful for lots of stuff as you need high voltage safely lots of times for testing for shorts. We trust our regular multimeters too much and they inject just 0,3V in resistance mode.If you don't go on anything that may remotely be dangerous like real power electronics a BM500 insulation tester may work for you.

author: Unknown
author_rank: Unknown
timestamp: February 21, 2018, 01:25:47 am
content: Quote from: PA4TIM on February 20, 2018, 07:01:06 pm^This^. Old paper caps in particular can often test OK at a lower voltage (or even their in-circuit operating voltage) but start leaking heavily between that & their rated voltage - they're faulty ones that just haven't failed yet, but soon will.I normally replace most paper caps on sight, but right now I've got a couple of unusual radios in the queue that deserve to be kept as original as possible. Original caps that test OK or come good after drying / reforming will be kept, & faulty ones will be re-stuffed where possible.At the moment I'm building a leakage tester based on the supply in the3rd schematic here, current-limited to 10mA and should be good for ~700V. I'll wait until it's built & tested before I post the schematic - most of the parts are from my junkbox/ebay, but I'm waiting for Mouser to get their finger out & send the MOSFETs & caps I ordered last week...

author: PA4TIM
author_rank: Super Contributor
timestamp: February 21, 2018, 08:04:47 am
content: QuoteDo you reform paper caps ? (reforming only works for electrolytic caps)And what do you mean by drying ?Are you talking about caps from very old radios (1920's or so) like the electrolytic cap on my picture (from a 30's Philips 836A that was damaged by a granate during WW2. the radio was from his parents)I restored a only a few radios (maybe 15 or so), but never replaced all caps. Only the ones that tested bad. The good caps worked fine for 50-60 tears and they all still work fine now.I know, this is a big nono in the audioworld where recapping is the magic word.(But I'm for most into testgear restorations, there the quality of components is probably just better)

author: Calambres
author_rank: Frequent Contributor
timestamp: February 21, 2018, 06:04:01 pm
content: I built a very good working Capacitor leakage tester / reformer following the instructions from M. Caldeira's very detailed youtube series:https://www.youtube.com/playlist?list=PLy5M_tA9ux7KWexvEjLB0SANSxQXi0zTSI also wrote an article on my build in my own web page. For those who can read spanish and may be interested, clickhere.My tester:

author: jsi
author_rank: Regular Contributor
timestamp: February 22, 2018, 05:25:10 am
content: Quote from: jsi on February 20, 2018, 12:38:57 amSCORE!!!!!!All I can say is make sure you marry a good woman. I told my wife to be on the lookout for any capacitor checkers at the estate sales. She then proceeds to tell me she'd bought some electrical "stuff" without telling me about it. Danged if she hadn't bought a Heathkit C-3 condenser checker and a Heathkit radio frequency generator. And, nobody wanted them so they were half price. They need to be rebuilt, but that's going to be far easier than starting from scratch.

author: bitseeker
author_rank: Super Contributor
timestamp: February 22, 2018, 09:35:38 pm
content: Nice score! Congrats!

author: notsob
author_rank: Frequent Contributor
timestamp: June 27, 2018, 08:42:46 pm
content: Mr Carlson has released a low voltage leak detector, all details are available from his patreon site, here's his release video