Equivalent of Obsolete Mains Rated Capacitor?

[sean0118]

Hi everyone,

I'm fixing an old sewing machine as a present for someone.

The problem was easy to spot, the capacitor that's over the motor, light bulb, neutral and motor earth was split and leaking oil. I think it's to stop the sewing machine from creating too much EMI, but I guess it's also possible that it allows the motor to start quicker? (The sewing machine does run without it, however I would still like to replace it).

I have two problems though. Firstly, the wiring diagram on it doesn't seem to be in English? I tried measuring the capacitance between each wire, but it seems well and truly fried.

Secondly, if I get replacement X1 or X2 capacitors how should I connect them? It's not possible to crimp directly to capacitor leads is it? Not that I actually have a crimper anyway...  any ideas?

[Paul Moir]

You're right about the EMI.  These are really important if the motor is using a centrifugal speed control, since the open contacts will arc without it.  Having no capacitor will cause these contacts to wear out very quickly due to excessive arcing, so even if you ignore the EMI it's important.

You'll want Y1 or Y2 capacitors to the green/yellow wire, since it runs to ground.  X is for across mains wiring.

I'm guessing it's German?
gr - grau - grey
g/gü - gelb/grün - yellow/green
sw - schwartz - black
w - wiess - white

Personally I'd just solder the old wires to the new capacitors.  I *might* try to fit them in the old capacitor's housing with the guts pulled out or some other plastic case.  Possibly pot them with epoxy.  Or just cover them all with a big piece of thick walled heat shrink tubing if I wasn't looking for a cosmetic job.

[sean0118]

Thanks. 

I have no idea if it has a centrifugal speed control, but I'll replace it and not take the risk.

You make a good point about the Y capacitor. The motor itself is a double insulated type, but I'm not sure if it's outer case is insulated, I'll have to check.

Also, I think German would be a good guess. It's a Leclanche capacitor from  Switzerland, looks like German is one of their four national languages. 


I think your also on the right track about soldering the new capacitor to the old wires, seems easiest.

Cheers 

[SeanB]

The 3 wire version of that capacitor is still in common use in appliances, so should be a spare part you can find in a white goods repair spares place. The other capacitor ( between black and white leads) is easy to replace with a 22nF 250VAC class X capacitor. If you cannot get it using 4 capacitors connected like the original will work, though you might not fit them all into the same space. If not then try to get them close to the motor itself.

[sean0118]

Thanks SeanB, I didn't know that, but I'll probably get four separate capacitors just because I'm trying to get it fixed asap.

One further question though. I know you can't use X capacitors in place of Y types, but can you use Y types in place of X types? Eg. can I use four Y types in this case?


Edit: I just checked and the motor case is insulated completely from the user, so I guess I could use all X type capacitors?

[SeanB]

You can use the class Y in place of the class X as the class Y has to have the same capabilities as the X but also cannot fail as a short under any circumstance, it must fail as open, even if self healing. The class X can self heal, but the Y cannot. not recommended, especially as class Y is only available in low values, typically max of 22nF.

[Seekonk]

If you are tight for space just put an X2 across the line and another across the switch contacts.  Y1 capacitors are a little overkill, but if you must use the common 470pf. .002 ought to be hard to find.

[macboy]

I would assume that the green/yellow is ground, so the two 0.002u (2nF) caps are Y type. The other two should be X type as they appear go appear to go across the line and from line or neutral to something else.

[sean0118]

You can use the class Y in place of the class X as the class Y has to have the same capabilities as the X but also cannot fail as a short under any circumstance, it must fail as open, even if self healing. The class X can self heal, but the Y cannot. not recommended, especially as class Y is only available in low values, typically max of 22nF.

Ok thanks, that makes sense then. The stuff they don't teach you at uni. 


I ended up ordering the following:

22nF, X2, ECQU2A223KLA
68nF, X2, ECQU2A683KLA
2.2nF, X2/Y2, ECQ-U2A222ML

The short leg ones will be annoying to solder the wires too, but element14 didn't have long leg options in those sizes...   


Just to clarify, the green/yellow wire connects to the motor housing which is double insulated and not earthed. But the 2.2nF capacitors I ordered are Y2 anyway so I guess there is no problems either way.