Motor Run Capacitor Safety Advise - Page 1
Forum section: electronics / beginners

author: adamboon
author_rank: Contributor
timestamp: July 02, 2016, 11:36:59 am
content: Hi,I ordered (and received) a whole bunch of these:http://au.element14.com/kemet/r75mn34704030j/cap-film-pp-0-47uf-400v-rad/dp/2456383?CMP=i-55c5-00001621To use as a Motor Run capacitor inside open reel tape machines.But I think I should have ordered these instead:http://au.element14.com/kemet/r463n347050n0k/cap-film-pp-0-47uf-300vac-rad/dp/2446250?ost=2446250&selectedCategoryId=&categoryNameResp=All%2BCategories&searchView=table&iscrfnonsku=falseIs the X2 rating important for safety for this purpose? It is behind a fuse, and not directly across the mains, as it's in series with the motor's winding. If there's less risk of fire or motor damage, i'll absolutely re-order the other part. What do you think?

author: Gyro
author_rank: Super Contributor
timestamp: July 02, 2016, 11:52:45 am
content: You will have a motor winding in series with the capacitor which should limit any spike current anyway (relative to being straight across the mains), what it lacks is certification testing for class X use. I would think it will be fine. Worst case the capacitance value might decrease over time, but motor-run capacitors do that anyway as they self-heal. Looking at the datasheet, the caps are designed for good pulse handling, electronic balasts, PFC, SMPS so they're obviously good quality.P.S. you said you ordered a 'whole bunch' of them, are you planning to put several in parallel to make up the required value? If so you might just want to get the equivalent value motor run cap for convenience.Edit: The voltage rating is a bit close (depending on your local mains) so the caps might self-heal and lose capacity a bit faster. You might want to wait for some other opinions too.

author: adamboon
author_rank: Contributor
timestamp: July 02, 2016, 12:07:19 pm
content: Quote from: Gyro on July 02, 2016, 11:52:45 amI've got 3 motors per machine, and a couple of machines... I think the bigger motors may have a couple in parallel, it's on a little sub-board though, So I'll just repopulate the way Studer intended. They originally had Rifa paper caps, but they dry out and fail. One of the machines has been "Fixed Up" a bit with some crappy parts, so I just want to change them out BEFORE they give me trouble.

author: Gyro
author_rank: Super Contributor
timestamp: July 02, 2016, 12:20:07 pm
content: In that case I'd take a look at the ratings of the Rifa caps (although most I've seen are X/Y rated). It's a wise decision to change them to the polypropylenes, they don't die gracefully when they start to crack (actually moisture getting in, not drying out) and the results are 'messy'.

author: adamboon
author_rank: Contributor
timestamp: July 03, 2016, 10:57:48 pm
content: They original capacitor is labeled:Rifa Mindprint PMZ 2015 CK2 0.47uF 150V~50Hz -40 to +60ºCI appreciate your advise and help - It's now more of a curiosity though, as I decided to not take any chances on safety - and have ordered the X2 part. The lead time is a bigger problem than the expense - but I thought it worthwhile for my piece of mind.

author: Gyro
author_rank: Super Contributor
timestamp: July 04, 2016, 08:14:15 am
content: QuoteIn that case, the motors must be running from a lower voltage winding on the mains transformer rather than directly off the mains (iirc 240V in Australia?). Your 400V parts will be absolutely fine in that case. Too late to cancel your order?