Replacing a Capacitor (Polaroid Processor)

[bvy]

It's a motor-start capacitor, which needs to handle significant surge currents. You CANNOT replace it with that tiny polyester capacitor linked above because it will explode.

Secondly, are you SURE it's 0.8uF? It looks much larger than that and I think 8uF is more likely but could be misjudging the scale of the photo. Can you post a picture of the identifying marks on the cap? Anyway, search for "0.8uF motor capacitor" on eBay; they'll be mostly 450V but that's a good thing and means it will have a longer life due to less stress on the dielectric. Expect to pay about $1-$2/uF and buy one that has a physical form factor that matches your old one so it's easy to mount.

Note that this capacitor handles mains power, and contains enough energy to hurt you. Be careful installing it and make sure there is no way that the leads can get near to contacting any other metal items like the chassis.

Thanks polyglot. It's most definitely 0.8 uF. I'm not in a position to post any pictures at the moment, but I've found (or was directed to) two other sources of folks using the 0.8 uF MP capacitor:

Post #5
http://www.largeformatphotography.in...-8x10-question

Post #20
http://www.largeformatphotography.in...how-much/page2

Still, if the MP capacitor is going to cause me problems (or harm!) I'm happy to avoid it in lieu of a better match. Problem is 0.8 uF capacitors are hard to come by in any voltage. The chassis, by the way, is hard plastic, but I'll take all the same precautions.

[polyglot]

What you have is a small-signal capacitor. It can block high voltages and has a lovely frequency response but it is not designed for power-factor correction, which implies continuous duty at significant current. It won't cause any great harm until it dies (probably with a pop), and it's a lot less toxic than the one you replaced. Just don't expect much life from it. I can't really tell from your photo whether it's wired as a start or run capacitor; in the latter case this will see a lot more voltage than the mains voltage, hence the need for a high rating and the propensity for the crappy 200V ones in these processors to explode messily.

The proper replacement will have a 400VAC+ rating, be resin-potted in a rigid plastic case with mounting hardware, and come with a datasheet including continuous-duty current rating of at least 150mA or so. Note also the presence of either heavy leads or screw terminals, not weedy little wires designed for PCB mounting.

Depending on the circuit, 1uF may also be a fine substitute.

[Amedeus]

I have a number of motor caps left over from my repairs ... Wired and terminated with spade connectors ... These are the no-oil variety and that's what I'm using in my 4 processors ...

I pay $7 each, ship them from China and connectorise them ...

Email me if I can help out

[bvy]

Thanks Rudi. I just sent you an e-mail...

[Sevo]

You want a 240V one - the 220V standard has been obsolete for decades...

[bvy]

I'm still at a loss as to what to buy -- some good but conflicting information has been offered.

Polyglot, is this the kind of "cased" capacitor you're referring to?
http://www.ebay.com/itm/Lot-of-4-Met...-/170262581032

[wombat2go]

Hi, Bvy,

Your capacitor is in the "hard to find" category. These days, capacitors around that value are not really required/ available , it must have been a small/ unusual motor.

What you need is a modern capacitor with type "X" or "X2" rating which means the manufacturer complied with various international standards to make it fail in a safer mode when connected directly across the 120 V or 240 V utility line.

I did a search and there are not many capacitors in 1 uF range that have type X compliance and are available in low quantities to consumer.

However, if you are in USA, here is one:
(1000 nF == 1 uF, Don't worry about the difference 0.8 ~ 1 uF for your application)

http://www.amazon.com/Amico-1000nF-P.../dp/B008DG9YP0

[bvy]

Thank you. That does look like a good match. What bothers me is that all of the start and run capacitors that I'm looking at (and I'm still not sure which I'm replacing -- "run" if I had to guess) look a bit more durable than some of what's been suggested so far. They have thicker insulated wire connectors or spade connectors -- not the bare "twist-tie" connectors that I'm seeing. Am I just being fussy?

[wombat2go]

Yes, to use the above Amico capacitor in your unit you would need to solder flexible tails on, and slide heatshrink back to cover the bare leads. The body can be attached to the case with silicon rtv.

If you want a 1 uF capacitor with isolated metal case and terminals, the problem is that motor capacitors are not readily available in such a small capacitance of 1 uF.
I suggest to search for an scr snubber capacitor. They will be larger, more costly and not easily available 1 off retail.
For example Ronken 64A79105K82 http://ronkenind.com/products.php

[bvy]

Really appreciate your help, wombat2go. I'm going to order the Amico capacitor(s) from Amazon. It seems like I can just solder the wires directly to the bare leads. I can sleeve some heatshrink in advance to pull over the bare leads and soldered joints when I'm done. Sound like a plan?