Sewing machine motor capacitor wiring? - Page 1
Forum section: electronics / repair

author: Pfaff84
author_rank: Newbie
timestamp: January 18, 2020, 02:52:18 pm
content: My Pfaff 84 sewing machine motor bogged down, stopped, and a loud pop and smoke rolled out.Sounds to me like capacitors, but I'm not sure. I cleaned the armature up and the brushes still have plenty of life.Can't figure out the wiring. It has a self contained dual capacitor with three wires coming in from the power supply end, one to each cap and another wire right in the center of the unit. Two wires coming out the other end, one to each field winding on the motor.What can I replace it with, and most importantly, how will I rewire it. I'm sure I can't find an exact replacement. The description on it is 2 X 2000 pF XY +.02 uf x (SW) 250V 4A HPFI've got pictures, but can't figure out how to post them on this forum yet!

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 18, 2020, 03:24:51 pm
content: EMI filter, not hard to find, harder to find on that will have the same dimensions.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 18, 2020, 03:34:44 pm
content: You could go for something in this style:https://www.ebay.com/itm/311439021611That would need mounting outside the motor though, as close to it as practical. Either that or don't care about interference and go without filter...You may find cylindrical 3 wire versions that fit, in that case center/yellow-green is earth, take live and neutral to your motor and parallel remaining filter wires with motor.If you search long enough you'll find one that fits, maybe even a 5 wire version.https://www.directindustry.com/prod/iskra-dd/product-40394-1848434.htmlhttps://www.amazon.de/dp/B011R18SQ8The thing is getting the right combination of keywords to search with in the U.S...

author: Pfaff84
author_rank: Newbie
timestamp: January 18, 2020, 04:02:41 pm
content: Thanks for that link. That's the only possibility I've seen that has the same wiring.I'm still trying to determine the purpose of that 3rd white wire coming in. Is that a ground wire?I don't really care if it has noise suppression or not. I just want to be able to know if the motor is still okay.If I knew that the white wire is a ground wire, I could disconnect the cap on the other end, cut the old cap open to expose the wires, and wire it direct to the field coils.??Sound like a plan?

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 18, 2020, 05:06:40 pm
content: Unless the EMI filter has inductors in it (and I see no inductance values on yours) there really is no point in having the 2 extra wires, 3 are enough. The white should be ground, prick a needle into the insulation and test continuity with the screw tab and plug ground to be sure if in doubt. (I wouldn't recommend this in most cases, but as you're going to remove the part anyway...)You may find this useful:https://www.emea.lambda.tdk.com/uk/faq/question.aspx?id=99

author: Pfaff84
author_rank: Newbie
timestamp: January 18, 2020, 06:22:12 pm
content: I did trace the wires from the input leads to the output side of the capacitors. I get conduction on the grey and black wires, but nothing on the white wire.Wouldn't this test confirm that the white is ground?

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 18, 2020, 08:03:50 pm
content: Quote from: Pfaff84 on January 18, 2020, 06:22:12 pmYes it would.

author: Pfaff84
author_rank: Newbie
timestamp: January 18, 2020, 11:31:15 pm
content: Thanks that's good to know. Shows how much I know!Anyway, now that that's confirmed...How can I test the motor without the caps inline? (To be sure it's just the caps).

author: james_s
author_rank: Super Contributor
timestamp: January 19, 2020, 12:48:02 am
content: Are you sure the capacitors are bad? That looks like a universal motor, the first thing I would suspect with symptoms like that is worn brushes that are no longer pressing against the commutator.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 19, 2020, 12:57:25 am
content: The quick answer is to power the motor with filter removed, for your safety make sure the motor itself has a ground connection one way or another.O.P. Did say that brushes were still nice and long, besides a pop /crack and nice puff of thick smoke is quite typical of the "Rifa / Schaffner" syndrome...

author: james_s
author_rank: Super Contributor
timestamp: January 19, 2020, 01:41:00 am
content: The motor should run fine from 12V, likely even 6V from a lantern battery or some alkaline cells in series. It won't develop very much power but it's a good way to test the motor without the risk of a spectacular failure.I've seen the suppression caps spark and smoke like that, but that doesn't explain why the motor slowed down, unless the fault current burned out the speed controller.

author: floobydust
author_rank: Super Contributor
timestamp: January 19, 2020, 02:51:05 am
content: I believe the EMI filter module has three capacitors. Two Y-caps 2,000pF and an X-cap 0.02uF plus some inductors. So I would check the capacitors for shorts.The speed controller board has many parts that would act as a fuse, you can use an incandescent light bulb as a load to check it. Although some controllers (Elna Stella) look at motor back-EMF to regulate speed. Those boards have the EMI filter at the mains input (with cursed Rifa caps) to stop TRIAC switching noise from getting out and just two inductors for a filter going to the motor.If a cap shorted the speed controller board might have gotten damaged.

author: mikerj
author_rank: Super Contributor
timestamp: January 19, 2020, 11:24:07 am
content: Quote from: james_s on January 19, 2020, 01:41:00 amA cap in the process of shorting out will be shunting current from the motor, the speed controller will have a limited output current capability (particularly if it's the old fashioned rheostat type pedal).OP, these parts are widely used on appliances with universal motors e.g. vacuum cleaners, blenders etc. and shouldn't be hard to find, The exact capacitance values will not be critical, they simply provide a low impedance path to shunt high frequencies so something in the ballpark will work ok. As someone else mentions don't get hung up on a part having five wires as a three wire part provides the same functionality and will be much easier to find. Googling "Three Wire Interference Capacitor" brings up numerous possibilities for me though all UK/EU based, but I would think they would be equally available in the US.

author: Pfaff84
author_rank: Newbie
timestamp: January 20, 2020, 11:28:00 pm
content: I found this information on a german site that specializes in Pfaff sewing machines, and offer this solution.The original 4A loadable filter of the motor was replaced by a simple, 6.5A loadable component in a capacitively similar X1 / Y2 circuit (Miflex X1 Y2 suppression capacitor KSPpz-10 0.1 microF 2x 0, 0027 microF 2.7nF).I can order that capacitor from Germany, but there is surely an american equivalent.

author: james_s
author_rank: Super Contributor
timestamp: January 20, 2020, 11:37:43 pm
content: Yes, you can easily order capacitors in those values in the US. You can probably find a very similar filter module too, it's really not critical at all, what you find doesn't have to physically resemble the original part as long as it fits.