Can't find low-ESR cap - alternative solution? - Page 1
Forum section: electronics / repair

author: sb1370
author_rank: Newbie
timestamp: October 16, 2020, 10:02:47 pm
content: HiI'm repairing my monitor power board and I found two blown capacitors which are from low ESR series. I could find a replacement for 680uf 25v cap which is 50v and have to fit it someway. But my problem is I couldn't find a replacement for 1000uf 25v with low ESR.I thought about using two 470uf in parallel to reduce ESR but according to the ESR formula it won't work cause by halving capacity the ESR doubles (in theory).I know I can order from the internet shops but the shipping costs outweighs the capacitor price and won't worth it.What's your suggestions? Also is it a right thing to not touching the other caps cause as I said I can't find the proper replacement.

author: ogden
author_rank: Super Contributor
timestamp: October 16, 2020, 10:09:14 pm
content: There is no such manufacturer part number "capacitor which is from low ESR series". Please be specific - what exactly capacitors you are talking about. I doubt that low ESR is key property in your case. Put new generic capacitors in and most likely you will be fine.

author: sb1370
author_rank: Newbie
timestamp: October 16, 2020, 10:26:08 pm
content: What? I have seen many of them. BTW it's GF series of Samxon.

author: wraper
author_rank: Unknown
timestamp: October 16, 2020, 10:38:31 pm
content: Quote from: sb1370 on October 16, 2020, 10:02:47 pm470uF capacitor will have higher ESR than 1000uf from the same series, however when you connect 2 capacitors in parallel, ESR basically halves. So two 470uF caps instead of one 1000uF is a viable solution. Or if those two 1000uF caps are in parallel, better use three 680uF capacitors instead.

author: precaud
author_rank: Frequent Contributor
timestamp: October 17, 2020, 02:05:18 am
content: All of the 1000uf 25v radial polar 'lytics of current manufacture I've measured recently have pretty low ESR, in the 15 to 25 mOhm range. To get one that isn't, you'd have to buy the cheapest junk available, or a series that is made to a higher-ESR spec, such as Nichicon PM series.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 02:18:58 am
content: Quote from: precaud on October 17, 2020, 02:05:18 amIt's not so much about ESR as such but that general purpose capacitors will not survive there for more than a few months due to high ripple current.

author: precaud
author_rank: Frequent Contributor
timestamp: October 17, 2020, 03:37:11 am
content: Quote from: wraper on October 17, 2020, 02:18:58 amPerhaps, but that's not his question.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 04:05:15 am
content: Quote from: precaud on October 17, 2020, 03:37:11 amHis question is about suitable replacement. General purpose capacitors are certainly not suitable to be there.

author: precaud
author_rank: Frequent Contributor
timestamp: October 17, 2020, 04:12:22 am
content: Quote from: wraper on October 17, 2020, 04:05:15 amWhere is "there"? He hasn't said where in the circuit they are. If they're post-regulator, ripple current will be negligible.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 04:14:46 am
content: Quote from: precaud on October 17, 2020, 04:12:22 amHere there:QuoteCapacitors on secondary side of SMPS/power input of CCFL inverter.

author: sb1370
author_rank: Newbie
timestamp: October 17, 2020, 07:25:21 am
content: Quote from: wraper on October 16, 2020, 10:38:31 pmHave you tried it in practice? because in theory ESR=tan δ / (C*f*2π) says otherwise. Unfortunately I don't have a ESR meter to measure it.Quote from: precaud on October 17, 2020, 02:05:18 amWell you are right the DF between general purpose and Low-impedance/ESR series isn't much different so in theory their ESR shouldn't be much different I can even get higher voltage ones for lower ESR, but I don't know how they are in practice. I think the more important factor here is "Ripple Current". Ripple current of a low-impedance series is twice the general one with the same ratings.Quote from: wraper on October 17, 2020, 02:18:58 amI agree with you, however I looked up the power board of another monitor newer but close to my model from the same brand and there they likely had used regular capacitors.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 07:48:20 am
content: Quote from: wraper on October 17, 2020, 02:18:58 amIt is very much about low ESRandhigh ripple current - combined. Low ESR capacitor will heat-up less, thus live longer. My consideration of suggesting generic (105oC) cap - most monitors do not consume much, thus ripple current may be tolerable for generic to live some 5 years or longer. There's always option to replace capacitor againI would not even consider putting multiple capacitors where is place for only one. What's the point of adding low ESR capacitors through long, inductive leads which have higher ESR/impedance than generic caps?

author: mzzj
author_rank: Super Contributor
timestamp: October 17, 2020, 09:12:47 am
content: Quote from: precaud on October 17, 2020, 04:12:22 amAnswer to "where?" is "Iran" and it might explain if OP has problems sourcing any components.

author: precaud
author_rank: Frequent Contributor
timestamp: October 17, 2020, 01:28:51 pm
content: Quote from: mzzj on October 17, 2020, 09:12:47 amGood point...Some cap makers list ripple current rating as a function of case size. So, if there's an absence of detailed info, the OP could put the largest cap he can find that will fit in there. Voltage rating can be higher than 25V, of course.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 01:33:51 pm
content: Quote from: sb1370 on October 17, 2020, 07:25:21 amI've never seen LCD monitor with general purpose capacitors in PSU on 12V+ rail. And overall they are almost nonexistent in SMPS, sometimes placed on some power rail with low current, while the rest use LOW ESR.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 01:36:30 pm
content: Quote from: ogden on October 17, 2020, 07:48:20 amEven some LOW ESR caps do not survive there for long. General purpose caps will pop very fast, hopefully without electrolyte spraying over the board. If OP can get 470uF LOW ESR, using general purpose capacitors is dumb.QuoteThe point is they will not fail. Longer leads will make no noticeable difference.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 01:58:44 pm
content: Quote from: wraper on October 17, 2020, 01:36:30 pmYes. - It will work when one of two capacitors is right where 1000uF needs to be and other is doing low freq bulk storage work.QuoteHold your horses. Extra length of capacitor leads will increase impedance at high frequencies, thus increase ripple amplitude on the PSU output. It's SMPS design basics - do not use extension cords for your filtering capacitors

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 02:04:25 pm
content: Quote from: ogden on October 17, 2020, 01:58:44 pmThen look at length of traces on those one layer PCBs. Also it's not like there are super high frequencies.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 02:26:50 pm
content: Quote from: wraper on October 17, 2020, 02:04:25 pmLook where exactly? Filtering capacitor connected to power rail through "length of traces"? Could you please show what you are talking about?QuoteBroadband noise of SMPS easily reach 20MHz. Inductance of 1cm long 0.5mm dia conductor is 7nH, impedance of such @10MHz equals 0.4Ohms. Take a moment to consume this.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 03:01:50 pm
content: Quote from: ogden on October 17, 2020, 02:26:50 pmTake a moment to consume there is easily 4-5 cm or more trace length from transformer to capacitor (each lead). And there is no solid ground plane as well. And PCB is located in a steel cage, so don't worry about electromagnetic emissions.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 05:49:44 pm
content: Quote from: wraper on October 17, 2020, 03:01:50 pmRight. So what. I talk about prolonged leads/tracks between filter capacitor and DC bus, capacitor connected to DC bus "through extension cord". If this does not explain what I mean then just leave it there and we better end this fruitless chat.QuoteSo what. There is condcted emissions as well. If you do not filter hi-frequnecy ripple in DC bus, then wires going out of steel cage become antennas. Also downstream circuit my not like unfiltered ripple.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 06:03:01 pm
content: Quote from: ogden on October 17, 2020, 05:49:44 pmDon't be ridiculous, additional centimeter or two from electrolytic capacitor leads will not make any significant difference in SMPS operating at about 30-60 kHz. It's not like extending leads of MLCC in a high frequency device. If you are so concerned about 20MHz, place 0.1uF MLCC with short leads in paralleland it will have much lower impedance than electrolytic cap at such frequency.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 07:02:32 pm
content: Quote from: wraper on October 17, 2020, 06:03:01 pmYou need to learn, kid.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 07:48:09 pm
content: Quote from: ogden on October 17, 2020, 07:02:32 pmYou need to learn to be realistic grandpa. Suggesting general purpose caps in a place where they will certainly fail instead of LOW ESR on somewhat extended leads is lame. Not that he will bring that monitor to EMC certification to begin with. And apparently you have completely no idea about monitor SMPS and how stressed those caps are. They run damn hot and at high ripple current.Quote from: ogden on October 17, 2020, 07:48:20 am

author: bdunham7
author_rank: Super Contributor
timestamp: October 17, 2020, 08:35:15 pm
content: Quote from: sb1370 on October 16, 2020, 10:02:47 pmI recently repaired my monitor power (brick) and had similar issues. The original caps were made to fit tightly and just barely meet specs, so they cooked. I was able to do a little grinding and make way for 35 volt caps, which were bit taller and had better ripple ratings. I don't know if you have the room for that.As for ESR and ripple...Don't obsess about the ESR in particular, instead try to find caps that have a ripple rating at least equal to the output current of the power supply circuit. And parallel caps do add up, so if you sub in two 470uF for 1000uF, just multiply the ripple rating X2. If you find caps that meet that requirement, the ESR is going to be fine--high ripple and low--or low enough--ESR ratings usually go together. I would make specific suggestions, but I have no idea what your parts availability is there. I'm sure it isn't easy.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 09:06:05 pm
content: Quote from: wraper on October 17, 2020, 07:48:09 pmYou may consider me grandpa, but apparently you are not up-to date with your knowledge about what general purpose aluminium caps are *today*. Other option: you think absolute noname crap equals general purpose. For me general purpose is something like Panasonic EEUFR1E102LB, while others may consider it low ESR with it's 0.018 Ohms and 2.4A ripple current @100KHz specs.

author: bdunham7
author_rank: Super Contributor
timestamp: October 17, 2020, 09:32:59 pm
content: Quote from: ogden on October 17, 2020, 09:06:05 pmWell, if 'others' includes Panasonic themselves, you'll note that the first listed feature in their datasheet for the FR series is 'Low ESR'. The FR series are a good product--10K hour @ 105C and generally good ripple ratings--but you'd be pretty much on your own calling them 'general purpose'. They are a premium product that is priced accordingly. I doubt the OP will have an easy time getting his hands on any.http://www.farnell.com/datasheets/2820375.pdf

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 09:54:42 pm
content: Quote from: ogden on October 17, 2020, 09:06:05 pmI know that their ripple current rating is generally more than 2 times lower than of average LOW ESR cap. Even if they have such rating at all. General purpose caps are about the same as 15 years ago, not much of change there. Panasonic EEUFR1E102LB can be considered to be almost an ultra LOW ESR cap, much better spec than what you generally can find in a power supply.QuoteYou basically are mocking OP by writing this

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 10:07:47 pm
content: Here is typical inexpensive but fairly decent general purpose cap Jamicon TKhttp://www.jamicon.ru/pdf/TK.pdfUsing 1.2 multiplier for >=10kHz (according to the datasheet), 1000uF 25V cap has 0.88A ripple current rating. General purpose available to OP probably is even worse. 1000uF 25V Samxon GF used originally is an entry level low ESR cap with 1.4A ripple current.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 10:21:34 pm
content: Quote from: wraper on October 17, 2020, 09:54:42 pmOh now you blame me that main brands are manufacturing aluminium electrolytic capacitors which all are essentially low ESRHow convenient. Back to the topic: better to put low ESR 470uF where 1000uF designed and add extra capacitance where you can find space for it. Yes I agree that using capacitors having ESR worse than 0.1 Ohm @100KHz will not do any good for decent runtime.Again: read the funny datasheets. It's all there.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 10:39:23 pm
content: Quote from: ogden on October 17, 2020, 10:21:34 pmYou remind me a famous phrase 'If they have no bread, let them eat cake!' Panasonic has general purpose series and even 85oC BTW, it's just you who buys their high end product. FR series you mentioned are explicitly stated to be LOW ESR in the datasheet, not "essentially."QuoteYou won't find brand new 1000uf 25V with such high ESR.

author: ogden
author_rank: Super Contributor
timestamp: October 17, 2020, 11:22:33 pm
content: Quote from: wraper on October 17, 2020, 10:39:23 pmWell, note that I mentioned "generic105oCcapacitors". Yes I agree that you have your point as well, no worries.QuoteYou are starting to use your head. Good

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 11:30:41 pm
content: Quote from: ogden on October 17, 2020, 11:22:33 pmNope, it's you who has not started using it yet. As you still don't get the difference between general purpose and low ESR capacitors. And preach Panasonic to OP from Iranto which no western distribuitor will ship anything. <0.1 Ohm does not mean they can survive a lot of ripple current. I can mention Panasonic NHG which @100kHz has about a half of ripple current rating of FR series (low values). Sort of general purpose, but almost qualifies as entry level LOW ESR for low capacitance but is not much better than Jamicon TK at 1000uF. Not that it's likely to be available to OP anyway.https://eu.mouser.com/datasheet/2/315/ABA0000C1215-1109177.pdf

author: precaud
author_rank: Frequent Contributor
timestamp: October 18, 2020, 03:22:52 am
content: This is eevblog at it's worse. OP's needs getting lost as the thread devolves into pettiness.

author: sb1370
author_rank: Newbie
timestamp: October 18, 2020, 07:25:54 am
content: Quote from: bdunham7 on October 17, 2020, 08:35:15 pmThanks, this is what I needed to know.Quote from: wraper on October 17, 2020, 11:30:41 pmYou guys are saying that like I'm from NK or a remote island, I can get brand capacitors from online shops in capital but for 2-3 caps it won't worth the shipping cost.I could find a high ripple 680uf 50v from samyoung LXV series (to replace 25v one) but I have problem fitting it (too tall), and for the 1000uf 16v one I found a 1000uf 25v from JWCO at my friend's place which is from LF series and low ESR and the datasheethttp://www.jiaweicheng.com/en/product/87919028.htmlclaims suitable ripple current ratings.Now the problems are:1. How can I fit the samyoung one? Maybe I have to settle with a JWCO?2. Can I trust JWCO?3. Is it better to keep the other good looking caps from samxon or replace them with JWCO?It's worth noting that the bulged caps have a common point, they are both placed before an inductor on the trace. So I think it's better not to touch the other caps.

author: wraper
author_rank: Unknown
timestamp: October 18, 2020, 11:45:44 am
content: JWCO is unreliable trash. Samxon capacitors are fine except GF and GK series made before 2010 or so.

author: bdunham7
author_rank: Super Contributor
timestamp: October 18, 2020, 02:23:41 pm
content: Quote from: sb1370 on October 18, 2020, 07:25:54 amWell, we don't know the particulars of your situation. For many of us the cost and availability of parts like that is a really trivial matter--like less than $5 for all of your caps including shipping and much less if they're riding along with another order. Would you be able to get better caps if you waited until you were ordering something else?Quote1. Perhaps use the JWCO for now with the intention of redoing it later with Panasonic FR or UCC-Nippon KZE types? Can you list the exact dimensions--length, diameter and lead spacing?2. Based on a web search, it looks like they're not great. That doesn't mean they won't work for a while.3. I don't know your exact configuration, but it sounds like perhaps a flyback converter with the initial output caps (the failed ones) followed by an output inductor filter and caps after that. The caps after the inductor see much less ripple, especially if the load is fairly steady. I wouldn't be in a hurry to change them out unless you can test them.

author: sb1370
author_rank: Newbie
timestamp: October 23, 2020, 06:52:12 pm
content: Sorry for the long delay. I soldered the caps and the monitor is working now. I also added a 470uf cap in parallel to the 1000uf one (from the same series) because I wasn't sure that its current ripple would be in range of the older one.Quote from: bdunham7 on October 18, 2020, 02:23:41 pmDimensions are 16 * 10 mm, forgot to measure lead spacing.