Bulging caps with very low ESR??? - Page 1
Forum section: electronics / repair

author: kgavionics
author_rank: Regular Contributor
timestamp: July 03, 2017, 06:49:55 pm
content: Hii'm trying to fix a plasma Tv.Took the tv apart and i found 2 3300uF 100V bulging caps.Took them out measured their Capacitance found 2800uf( within the 20% tolerance) and was surprised that they have a low ESR around 0.035 ohm ( for that type of caps ESR <0.1 ohm is good).I did my trouble shooting and didn't find any problem with the other components.i want to know how can these caps measure good and have pretty bad bulge.

author: wraper
author_rank: Unknown
timestamp: July 03, 2017, 07:07:50 pm
content: When they are bulged but not vented the gases yet, often they still have good ESR. Post a picture.

author: kgavionics
author_rank: Regular Contributor
timestamp: July 03, 2017, 07:10:01 pm
content: Quote from: wraper on July 03, 2017, 07:07:50 pmupdated my previous post with a picture

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: July 03, 2017, 07:11:54 pm
content: Bulging caps are bad news, imminent failure, replace them.

author: wraper
author_rank: Unknown
timestamp: July 03, 2017, 08:26:26 pm
content: It's not common for KMH series to bulge. Also cap on the right looks like it has a few tiny holes on top, but off center, not on the vent. I've seen such happening if there was rapid surge through the capacitor, like when rectifier fails and AC goes into the capacitor.

author: kgavionics
author_rank: Regular Contributor
timestamp: July 03, 2017, 08:52:28 pm
content: these two caps are not the filter capacitor after the main bridge rectifier,they are from the output stage(Va and Vs voltages) that goes to the PDP module.

author: PA4TIM
author_rank: Super Contributor
timestamp: July 03, 2017, 09:01:34 pm
content: For the future if you want to know if a cap needs` replacement: forget ESR, it is only an indication based on some obscure tables. OK, it is a handy tool usable with some experience but if you want to really know if the cap is still good an ESR meter is useless. Besides that, a shorted cap can have a very low ESR. Repaired an industrial powersupply last week. On cap with a high D, the rest leaked so much the LCR meter showed Rs at 120 Hz instead of Cs.Do this to be shure the cap is dead (bulging is dead, no need to measure):1) Use a decent LCR meter that also states D and measures at 100/120/1000 Hz, higher is a bonus2) Find the datasheet :http://www.chemi-con.co.jp/cgi-bin/CAT_DB/SEARCH/cat_db_al.cgi?e=e&j=p&pdfname=kmhlug3) Look up the specs:100V 3300uF is a tan d (= DF = D) of 0,15 max new at 120 Hz4) do the math: That is a reactance of 0,4 ohm at 120 HzThe ESR at 120Hz is 0,15 x 0,4 = 0,06 ohm max for a new cap.The end of live value for tan d = 200% = 0,3 and that is 0,12 ohm at 120 Hz.They do not state the impedance (Z) at 100 kHz in this case so it is not possible to calculate the ESR at 100 kHz. Often they do and then you can calculate the ESR at 100 kHz from the reactance and impedanceWhy they almost never state ESR at 100 kHz is the wrong question. Why do people measure ESR at 100kHz is the right question....(if have 1 time seen ESR in the specs at 100 kHzbut that was for SMD polymer caps)5) Measure capacitance, and not with a multimeter, that only works for new caps , a high ESR causes a much higher capacitance reading. So useless, use a decent LCR meter.6) Measure leakage current, for this cap 0,02CV = 0,02 x 3300 x 100 = 6600 uA but the datasheet states also not more as 3mA. I test a lot of caps and most caps leak not more as 50-100uA.

author: kgavionics
author_rank: Regular Contributor
timestamp: July 03, 2017, 09:08:53 pm
content: Quote from: PA4MTI on July 03, 2017, 09:01:34 pmThank you PA4MTI for these useful information.

author: Armadillo
author_rank: Super Contributor
timestamp: July 03, 2017, 10:15:36 pm
content: Quote from: PA4TIM on July 03, 2017, 09:01:34 pmIn regards to the frequency of measurement, manufacturer generally conform to the industrial accepted standard method of measurement to qualify their capacitors [See attachment]. Essentially the method is to obtain more accurate readings from the various ranges of capacitance.Quote from: PA4TIM on July 03, 2017, 09:01:34 pmEhm!.... Would you want to derive that in Maths? I think it's your personal observation but generally is not true. The 2 entities are different. Many times, high ESR and drop in capacitance value were observed. Would you care to elaborate your findings?ESR should be viewed as a measure of the quantifiable wastage of energy, compare to its reactance as an indication of acceptance criteria norms.

author: ovnr
author_rank: Frequent Contributor
timestamp: July 03, 2017, 10:20:01 pm
content: Quote from: Armadillo on July 03, 2017, 10:15:36 pmI think what PA4TIM is saying is that a cap with a high ESR will erroneously be read as having a higher capacitance than it really has, because multimeters are usually terrible LCR meters.

author: PA4TIM
author_rank: Super Contributor
timestamp: July 03, 2017, 11:09:56 pm
content: That is indeed what I'm trying to say. DMM' s measure capacitance through measuring the time it takes to charge and decharge a cap to a certain voltage. The ESR increases that time so the DMM shows a value that is to high.QuoteYes, I know, that is why I talked about ESR @ 100 kHz. The manufacturers do not state the ESR at 100 kHz. So you can do nothing serious with the measured value. Except if they state |Z| at 100 kHz, then you can calculate Rs but I woul;d not do that. With 3300 uF you are at 100 kHz probably above the SRFBesides that ESR is not a constant. It very high around DC, drops fast to the lowest point and after that it goes up again. The lowest point is often somewhere between 10 kHz and 50 kHz but depends on several factors. So measuring it at 100 kHz gives a value that is not usable as substitute for the ESR at 120 Hz

author: Armadillo
author_rank: Super Contributor
timestamp: July 04, 2017, 01:14:59 pm
content: Quote from: PA4TIM on July 03, 2017, 11:09:56 pmUsing Cheap multimeters and a 22uF 25vdc capacitor with a simulated increase in ESR by 10 ohm as comparison.Please stay contemporary with your definitive assertion.Would appreciate your demonstration in return.Not entirely untrue and I understand the square wave method and the problem you raised but those must be yesteryear meter. Would you please examine.Thanks.Edit: Updated with correct frequency

author: alm
author_rank: Super Contributor
timestamp: July 04, 2017, 01:34:10 pm
content: Of course an LCR meter in parallel mode will give incorrect values for a series circuit. What did the LCR meter indicate in series mode? How did the DMMs behave with parallel resistance (i.e. leakage)?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 04, 2017, 03:58:40 pm
content: Someone had asked me this same question when I was looking at the Gossen. If you watch the first few minutes, I ran a similar test.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 04, 2017, 04:01:56 pm
content: Also, YT recommended this video to me the other day where several antique capacitor testers are shown. I like old equipment like this.

author: Armadillo
author_rank: Super Contributor
timestamp: July 04, 2017, 04:28:17 pm
content: Quote from: joeqsmith on July 04, 2017, 03:58:40 pmGreat video, if I have known you have done it, wouldn't have spend the time.The LCR meter, what frequency are you basing on?

author: PA4TIM
author_rank: Super Contributor
timestamp: July 04, 2017, 07:00:15 pm
content: Armadillo: First about your LCR meter.The 19,38 uF is Cs, series capacitance, D=0,182 so Xc=8,2 ohm Rs=1,49 ohm Z=8,334The 6,431 uF is Cp, parallel capacitance, re-calculating with D=1,45 gives Cs=19,95 uF, Xc=7,977 Rs=11,56So your meter is correct, but I hope the meter tells you it is measuring Cp instead of Cs. Cs = Cp only if D is very low.I do not know what you mean with a squarewave. The meters I measured to test Capacitance after repair used DC to charge the cap and measuring the time. See several service manuals from for instance Fluke. You can measure ESR with a squarewave.Then the multimeter test, here I'm surprised because I never tested it like that on a DMM. (I did for bridges to calibrate D) My theory is based on experience with caps with real bad ESR and not simulated ESR. So I now tested both situations. And indeed with 39 ohm simulated ESR both my DMM's see almost no difference in capacitance. I can not explaine that. But a real bad cap does what I wrote. (i have tested that many times in the past. see for instance the picture below from a test on caps together with a TV repair man the results are from his caps and his meters checked by me.)If I find time I will do more measurements and make a video and blog page about that.My short test like yours and Joes:100uF panasonic FMIET DE-5000 93,15 uF, D=0,057 at 1 kHz 95,61 uF and D=0,019 at 100Hz,Agilent U1252A DMM 101,5 with Rs=39 ohm and 101,4 withoutBrymen BM869s DMM, 92,2 using the 39 ohm and 98,9 withoutI measured some more but results are about the same:IET: 10,087uF D=0,112 at 1 kHzIET 10,084 uF D=2,54 at 1 kHz with 39 ohmAgilent 11,03 uF alone versus 11,00 with 39 ohmBrymen 10,85 uF alone versus 10,77 with 39 ohmThat is all nice but these are good caps with a series resistor. I always keep a small collection bad caps for testing. I have a lot of LCR meters, bridges, leakage testers and RCL standards. My pride and joy a GR-1620 that comes out GR's own standards lab. For my daily work (repair of measurment gear and calibration gear) I use a IET DE-5000.So I took a real bad 470 uF, the IET: Cs 276 uF with a D=1,092 at 1kHz Xc=0,576j Rs= 0,6296 ohm. So no extreme ESR if you look at ohms (but a D of 1 is bad)The Brymen: 457,3 uFSo if you would measure this cap with an ESR meter and C with a DMM it would be a perfect capAnd a bad 100 uF, IET: 76,45 D=1,281 at 1 kHz, Xc=2,082 j, Rs=2,081 D is bad, capacitance is just outside specs (20%)Brymen: 108,3 uFI did not note the Agilent because it was in the same ballpark as the BrymenSo now the 1000 dollar question, why do they ignore a real series resistor upto a certain level like Joe showed but go very wrong with a real bad cap (like I told before)I did not test more because an industrial calibrator is spread out in pcb's all over my bench for testing so no room.

author: Armadillo
author_rank: Super Contributor
timestamp: July 04, 2017, 08:06:08 pm
content: I am happy that all technical like minded people here are contributing to this constructive discussion of a rather puzzling subject.The next pertinent question is if we simulate an increase in ESR by putting a resistor in series, will it be similar looking waveform as seen in an oscilloscope to validate the experiment.The answer is Yes, done it today, the resistance drop portion is merely elongated.Technical people know of the need to conform to the industry standard frequency of measurement for measuring capacitor. By the way, How much does a 1 Mega hertz LCR meter cost?So frequency of measurement is important and costly subject.Then using multimeter to measure capacitor can only be an indicative figure if the frequency of measurement is unknown.If someone can find a faulty ESR increased capacitor, do share the findings.Thanks.

author: Armadillo
author_rank: Super Contributor
timestamp: July 04, 2017, 08:13:15 pm
content: Quote from: PA4TIM on July 04, 2017, 07:00:15 pmBy the way, please conform to the standard frequency of measurement to validate the data so that it could align well with other instruments measurement results.

author: kgavionics
author_rank: Regular Contributor
timestamp: July 04, 2017, 11:21:52 pm
content: In my experience it was easy to locate faulty capacitor by using a cheap chinese ESR meter (MESR 100 V2).My only concern this time was the low ESR of the 2 bulging caps.sometimes we have to make thing easy and not complicate thing.that how we do it here in canada and US..Sent from my GT-I9505 using Tapatalk

author: joeqsmith
author_rank: Super Contributor
timestamp: July 04, 2017, 11:37:22 pm
content: Quote from: Armadillo on July 04, 2017, 04:28:17 pmThat was ran at 100Hz.For high frequency, I just use my antique VNA with LabVIEW to do the calculations.

author: Armadillo
author_rank: Super Contributor
timestamp: July 05, 2017, 12:09:08 am
content: Quote from: kgavionics on July 04, 2017, 11:21:52 pmI think joeqsmith is from the US and he is more advance using Labview, much complicated.That MESR 100 is for the beginner and can give error as large as 100%. I am not joking. Maybe some US people can convince you.Hey, but as long as you are happy with the low ESR reported, that will be all good.And by the way, thanks for supporting chinese product. Cheers

author: kgavionics
author_rank: Regular Contributor
timestamp: July 05, 2017, 12:24:54 am
content: guys don't get me wrong.i didn't want to offend anyone,but my point was that finding a bad cap is not rocket science.Even with the crap chinese Esr meter i fixed a lot of boards with bad capacitors.

author: Armadillo
author_rank: Super Contributor
timestamp: July 05, 2017, 12:49:23 am
content: Quote from: kgavionics on July 05, 2017, 12:24:54 am

author: peteb2
author_rank: Regular Contributor
timestamp: July 05, 2017, 05:02:56 pm
content: In all the 30+yrs of repairing all manner of electronics i must say the entire subject on dying caps is a real eyeopener and hugely common issue. In the rush to make things occupy less space the same amount of generated heat still has to go somewhere, somehow. I see layouts designed with say a 330uF-100V cap jammed hard up against the onboard heatsink of a power semicondctor that runs HOT thus boiling hell out of the cap. These days if the equipment has been powered on permanently, done long service or hard work or has run a high temperature because of overloaded or broken fans... I simply replace all electrolytics on spec irrespective of whether they measure OK for values or ESR.The other condition for replacement is if the item contains the OneHungLow brand of cap... if you get my drift... and that bit of gear is mission critical or else i tell the owner to buy something truly reliable (especially if it's for a business and part of main income)...I guess i am lucky the end user/ owner of the gear usually doesn't mind the extra expense of my time and buying name-branded fresh as possible replacements but i can so see that in some cases there's someone who wants only the cheapest of cheap fix... I then say well it'll very likely it'll breakdown again in a few weeks.

author: kgavionics
author_rank: Regular Contributor
timestamp: July 05, 2017, 07:30:14 pm
content: by the way i tried what Joe smith did in the video, i put a small value resistor in series with the capacitor and the Chinese meter gave me every time the value of the esr + the series resitor.So, the meter isn't that bad for its price.