Deliberately inducing high ESR failure in electrolytics - Page 1
Forum section: electronics / projects

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 02:50:51 pm
content: Hi, I want to demonstrate the behavior of faulty electrolytics in a forum post, for educational purposes. But the problem is, I don't have any electrolytics lying around that are in an high ESR failure mode. So my question is, how can I take a good electrolytic cap and put it into this failure mode? For example, would keeping it in an oven at 150 for an hour work? I don't want to just try it, because the fallout of a blown cap in wife's oven would be disastrous

author: KhronX
author_rank: Frequent Contributor
timestamp: March 28, 2018, 03:03:37 pm
content: I don't suppose adding a series resistor with it is an option..?

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 03:15:02 pm
content: I'd rather work off of a genuine failure, rather than a simulated one.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 28, 2018, 03:31:19 pm
content: Putting the capacitor in an oven at a temperature well above the max rated operating temp while imposing a voltage well over the max rated voltage would probably do the trick. How long it would take is kind of hard to predict.Barely placing the capacitor on its own in an oven may not do much or may take ages to degrade it, unless you set a very high temperature that may set it on fire, which is not what you are after. Likewise, only imposing a voltage that significantly exceeds its rated voltage at room temperature may take ages to degrade it, unless you set too high a voltage, in which case the capacitor will end up exploding. The added benefit of the oven is that if it ever explodes, the mess will be confined inside the oven. An electrolytic cap that explodes can make a real mess.So I would try a reasonable combination of both and evaluate the result every 24 hour or so.

author: SeanB
author_rank: Super Contributor
timestamp: March 28, 2018, 04:35:37 pm
content: Simple enough, apply around 3V reverse voltage, limited to 500mA for around a half hour. Before punch a small hole into the aluminium case to vent the pressure, and the capacitor will boil itself dry pretty fast.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 04:58:22 pm
content: Quote from: SeanB on March 28, 2018, 04:35:37 pmOk, I've set that up. Initial capacity was 1750 uF (2200uF, 16V part), initial ESR was 0.05 Ohms.I have punched a tiny hole to the top of the cap and have connected it to 3V, with 500mA limit. Initially, there was about 1 mA current draw. That has increased now to 4 mA and there are bubbles coming out of the vent hole. It looks like the current has stabilized at 4 mA. I'll let it cook for a while and then check again!

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 28, 2018, 05:15:02 pm
content: The datasheet criteria for failure is usually a doubling of dissipation factor, caused by max temperature operation for x hours, the lifetime they usually publish. I'd think running at high ripple current- AC drive with a limit resistor, would get you there in a reasonable amount of time.ESR became popular/useful with the advent of switching supplies. For line applications and most other things, dissipation factor is the thing to use. Naturally you can convert value and loss in any unit system to any other unit system, but esr is typically a high frequency measurement. It's unusual for the esr component to become a factor in low frequency applications, as the reactance usually dominates.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 05:40:04 pm
content: The main point I want to get across to the kids is that, the nice, expensive multimeter with a capacitance range is not enough to tell whether a capacitor is working properly or not. The multimeter might measure a capacitance, but the high ESR will prevent that cap from doing its job.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 28, 2018, 06:19:20 pm
content: Well. Yeah. Reverse polarizing polarized electrolytic capacitors is a sure way of making them fail fast and hard. I didn't mention this approach because as you have seen, this is very close to complete destruction in a short amount of time. Not punching a hole in it would have led to guaranteed explosion. I bet the aggravated ESR is not the only problem your capacitor now has.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 06:23:28 pm
content: I just removed the cap and wiped it off. During the whole test, I had removed 3 drops of electrolyte from it so far. And just before I removed it, the current was back down to 1 mA. The temperature of the cap was always low, even when the electrolyte was bubbling out of the hole.When I measure it, the cap still is at 1560 uF and ESR is 0.06 Ohms. So it got worse, but very little.So I guess this needs to be pushed a little harderI'll try 12V now.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 06:31:47 pm
content: With 12V, the current immediately shot up to 500mA and the PS started to current limit. And the cap got really hot. After 1 minute, I removed the cap and measured again:1450 uF, ESR = 0.1 OhmI then connected it back to the power supply with a current limit of 250 mA, because with 500 mA it was creating too much stink in the room.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 06:46:42 pm
content: After 5 additional minutes of heat therapy, the cap was down to 910 uF. And ESR is now 0.16 Ohms ... I actually had to remove the cap because the outside plastic started to smoke.But here is what I noticed, too. Before starting this last 5 minutes, the power supply was limiting the current to 250 mA and the voltage was around 6V. But as time went on, the voltage gradually increased and just before I turned off power, the voltage was a little above 10V. I guess as the cap dried out, it got worse at conducting electricity.So connecting an electrolytic in revers is a sure way of ruining its capacity and ESR. But you need to apply sufficient voltage to have a strong effect.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 06:49:42 pm
content: And, after letting the cap cool down to ambient, capacity is now 780 uF and ESR stands at 0.2 Ohms.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 28, 2018, 07:02:52 pm
content: What's the test frequency? If it's the usual 100kHz, you've got about 100% dissipation factor, that is, resistance about equals reactance. Definitely a bad cap! IMO, whenever one talks about cap parameters, it's important to always state test conditions. Capacitance must be noted as series or parallel model, frequency and if possible, test voltage.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 07:09:23 pm
content: Quote from: Conrad Hoffman on March 28, 2018, 07:02:52 pmTested with a keysight U1733C at 1 KHz. Series model is indicated on the display, but don't know what the test voltage is ...At 100 KHz, capacitance is 870 uF and ESR is 0.3 Ohms.

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 07:13:15 pm
content: Just checked the dissipation factor, too.100 KHz, D = 0.1681 KHz, D = 1.07

author: RoGeorge
author_rank: Super Contributor
timestamp: March 28, 2018, 07:16:26 pm
content: Just order an assortment kit bag of electrolytic capacitors from AliExpress.There you have it, many of them will be DoA.P.S. I'm not joking, I ordered such a kit a couple of years ago.Bad memories never fade out.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 28, 2018, 07:18:30 pm
content: Ah, by those numbers the cap isn't so bad. Here's a converter you might like (first item)-http://www.conradhoffman.com/chsw.htm

author: taydin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 07:35:36 pm
content: Quote from: RoGeorge on March 28, 2018, 07:16:26 pmYep, shopping from aliexpress is pretty much like throwing diceMy last order took 2 months to be delivered ...

author: cat87
author_rank: Regular Contributor
timestamp: April 03, 2018, 07:38:19 pm
content: Ideally you'd want to pulse a capacitor with high enough current and frequency (detect the frequency at which capacitor impedance is small enough so that the ripple current is huge) and leave it like that for a few hours. The high current ripple and most likely the high temperature will prematurely age the cap and dry out the electrolyte.It's very hard to condense years worth of use into half an hour or an hour and the end result may be different, but if only high ESR is the goal, I'm thinking maybe you can either set up a simple half-bridge or H-bridge tied to a stout PSU and use that as the high current pulser, with the proper drive signals, of course. That might do it.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 03, 2018, 08:50:24 pm
content: The idea that aluminum electrolytics dry out is real enough, but don't forget that they're not full of water! The electrolyte base is one of various things like a glycol. The vapor pressure should be down around 0.1 mm of hg, not up at 17.5 for water, depending on just what they used. That means it's a lot harder to dry them out. BTW, avoid breathing whatever it is you're driving out of them.

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2018, 03:34:16 pm
content: Go to the dump and pick up some old electronic items. Some will work but the ones which don't will quite likely have bad electrolytic capacitors.

author: The Electrician
author_rank: Frequent Contributor
timestamp: April 05, 2018, 01:55:45 am
content: Quote from: taydin on March 28, 2018, 05:40:04 pmYou might find this post relevant:https://www.eevblog.com/forum/testgear/about-capacitance-measurement-with-dvms/msg489690/#msg489690

author: taydin
author_rank: Frequent Contributor
timestamp: April 05, 2018, 07:53:54 pm
content: Quote from: The Electrician on April 05, 2018, 01:55:45 amThat is good information, thanks a lot!

author: cvanc
author_rank: Frequent Contributor
timestamp: April 06, 2018, 02:57:14 pm
content: For what it's worth, I always keep a small handful of the defective electrolytics I pull from repairs I'm doing.I find it's useful to verify that my LCR meter can still identify a known bad part. Plus they're very handy if you need to teach someone else how to use an LCR meter.