Help identifying old capacitors for a repair job. - Page 1
Forum section: electronics / repair

author: Antipixel
author_rank: Newbie
timestamp: August 08, 2022, 01:22:07 pm
content: Hi,I have a blown cap that I cannot find a new replacement and would appreciate help finding a good substitution, as well as a cap this one has vomited all over which I would also like to replace as well as a precaution. [Warning graphic pictures included]To what I could find online the blown capacitor is a filter caps for the sewing machine, while I know they are not strictly necessary I would like to install them back, cheer up my mum a bit.https://flic.kr/p/2nD6AAZand from the other sidehttps://flic.kr/p/2nD7LJU1: Rifa PME 271 M610 100nF X-class 250V~MP CP2 GPCI cant find a new replacement for this cap at all, but know enough to avoid old stock of these because of plastic cracking issues. I have no idea what the MP, CP2, or GPC stand for. Can I replace this with a X2-class? Why is it paper, must it be paper? Are there any benefits to paper? Many questions on this one.So far can only find this paper one around my neck of the woods [https://asset.conrad.com/media10/add/160267/c1/-/de/000456756DS01/tehnicni-podatki-456756-wima-mpx20w3100fg00mssd-1-kondenzator-za-odpravljanje-motenj-x2-radialno-ozicen-01-f-250-vac-20-1-kos.pdf].https://flic.kr/p/2nD6ABW2: Plessey 10nF K 250V~ X2All the other numbers on this cap confuse me and would love to hear an explenation of what they are. No idea what type it is I just assume it's paper like the other one. Am including a picture of the same type of cap just the one that was not vomited on and easier to read.N.B. My mother is quite attached to this sewing machine so my head is on the line and cheapening out for a few € saving on two caps is absolutely out of the question.PS: Can include a photo of the whole board if someone is interested to study it for fun.

author: alm
author_rank: Super Contributor
timestamp: August 08, 2022, 02:10:26 pm
content: 1. I'd replace it with a 100nF X2 cap with a voltage rating of 250Vac or higher (275Vac is common) with the same lead spacing. Get metalized polypropylene (MKP) or polyester (MKT), not paper. Polypropylene is more durable than paper and less likely to burst like this. They should be easy to find at any parts distributor.2. Same specifications as #1, but 10nF.Regarding some of the other markings, I imagine 40 85 21 SH might be a date / batch code. Like week 40 (or 21) 1985. Other marks and numbers, like VDE, are related to approvals and compliance. MKT means it's ametalized polyestercap. I 1.58.00 is probably a part number. None of this information, except MKT, matters for finding a replacement for repair.

author: Antipixel
author_rank: Newbie
timestamp: August 08, 2022, 06:32:00 pm
content: Thanks!As a physicist I only had basic electronic cirquits. So I can calculate the needed capacity and voltage. Everything else is quite arcane and have a hard time finding out more about.Our of curiousity: Why are Paper caps still out there? Surely they have to have a benefit. From what I can find online it only states that they are cheaper than MKP. But when I look in my local stores the paper ones [of my specs] cost 2€ while MKP are an order of magnitude cheaper 0,2 - 0,4€Also how bad would it be to pop in a 275VAC instead of a 250 [more options in the online store]?As for the markings the 40 85 21 one is one of the few I happen to know. It is temperature range. The cap is good between -40°C and 85°C and surviving 21 days under a certain set of harsh conditions [that I don't know exactly]No idea what the SH means though.

author: alm
author_rank: Super Contributor
timestamp: August 08, 2022, 06:51:49 pm
content: Quote from: Antipixel on August 08, 2022, 06:32:00 pmI have no idea why anyone would use a paper cap these days, except audiophiles who'll try anything and generally don't worry much about measuring anything.Quote from: Antipixel on August 08, 2022, 06:32:00 pmAny value >= 250V will work. 400V would also be fine if the price and size are okay.

author: Per Hansson
author_rank: Unknown
timestamp: August 08, 2022, 07:22:09 pm
content: Quote from: Antipixel on August 08, 2022, 06:32:00 pmYou can learn it from the datasheet, SH means "Self Healing"https://www.elfa.se/en/x2-capacitor-100nf-275vac-630vdc-20-kemet-pme271m610mr30/p/16564686However the datasheet also says this so I am not 100% sure of its trustworthiness:"The highest possible safety regarding active and passive flammability""The impregnated paper ensures excellent stability and outstanding reliability properties, especially in applications with continuous operation"Quote from: alm on August 08, 2022, 06:51:49 pmThe old Rifa (now Kemet) Metallized Paper caps do have a higher dV/dt rating compared to modern Metallized Polypropylene capacitors.

author: Antipixel
author_rank: Newbie
timestamp: August 08, 2022, 10:31:10 pm
content: Thanks!I'm no expert but I'd imagine a small sewing machine motor maybe might not need a MP cap with higher dV/dt. Don't think that little thing pulls that much, also feels like it has soft engine start as well as a soft stop.

author: Per Hansson
author_rank: Unknown
timestamp: August 09, 2022, 07:44:18 am
content: Quote from: Antipixel on August 08, 2022, 10:31:10 pmNo there is no problem with the capacitor alm suggested in this implementation, I just wanted to provide a possible reason for why the paper caps are still being soldI'd recommend something like this for the replacement, just check lead spacing and size in general fits:https://www.elfa.se/en/x2-class-aec-q200-metallized-polypropylene-film-capacitor-100nf-310vac-630vdc-10-kemet-f862bk104k310zv054/p/30181980

author: Haenk
author_rank: Super Contributor
timestamp: August 09, 2022, 12:05:38 pm
content: To my knowledge, 275V types are mandatory in 230V EU countries. Don't use 230V types, unless you have 100-117V only units.RIFA X2 275V as a replacement should be available almost everywhere.

author: Antipixel
author_rank: Newbie
timestamp: August 09, 2022, 12:39:58 pm
content: QuoteWill take both of your advice and see what I can find localy. The smaller cap wont be an issue, just the larger has a 20mm lead spacing. Might have to buy a pack of 5 which still beats shipping costs. Are there any special storage needs for these apart from dry, dark and cool? I imagine I don't need to short them out for long term storage.EDIT: 22.5mm in a 20mm hole wouldn't beneat und tidy, would it?

author: Haenk
author_rank: Super Contributor
timestamp: August 09, 2022, 01:00:14 pm
content: "Dry" storage would be a good idea, otherwise they are pretty robust. *I* would just bend the wires a bit to make it fit, as long as it fits in otherwise, there is no technical disadvantage.

author: Antipixel
author_rank: Newbie
timestamp: August 09, 2022, 09:46:55 pm
content: Quote from: Haenk on August 09, 2022, 01:00:14 pmSilly final question. Around here cant find 20mm 100nF X2 MKP caps, either 10€ for ordering abroad or a min order of 500 caps.Localy I have on offer 22,5mm terminals MKP caps 20mm fresh MP caps [All of the relevant specs for me being the equal].Which would you go for? Paper cap or slightly bending the pins to make it fit?

author: nightfire
author_rank: Frequent Contributor
timestamp: August 09, 2022, 11:20:35 pm
content: As long as the capacitor stands solidly on the PCB, and is not able to vibrate loose, I would bend the legs slightly. In general, it might not be a bad idea to add some silicone goop (non-acetic) to really affix it to the PCB and dampen possible vibrations.

author: alm
author_rank: Super Contributor
timestamp: August 09, 2022, 11:53:06 pm
content: 20 mm vs 22.5 mm lead spacing is 1.25 mm on both sides. I would also bend the leads over a paper cap, or paying a ridiculous price. It might be that modern creepage requirements from IEC standards dictate the 22.5 mm lead spacing in more modern parts.