Sewing motor capacitor...how to read, what to buy to replace. Looking for assistance.

Thread Starter

Da Taz

Joined Jan 31, 2024
7
Hello, and hi, hey and yo!

I am, admittedly not a brain trust when it comes to certain types of electronics. I do know a bit about not electrocuting myself, and about circuits, motors, etc...etc...you get the picture.

OK. So I am restoring an old 1.0 amp sewing machine motor. I did all the right things, changed out the brushes, cleaned up the can, rotor, stator and commutator (she gleams like a brand new penny now). Bearings oiled, wiring about to be rewired, and then there's this lovely little "noise reduction" capacitor that I believe is a "start/run" cap that keeps the machine from surging when you hit the machine's pedal. I've heard it called other things but its purpose is to filter out noise so that outside electronics don't pick up noise from the machine's circuit being connected to the house. I guess once upon a time that was a thing. But I digress. The main reason it is in circuit with the motor is to keep the pedal from sending too much voltage through the brushes when the motor first engages.

So here is my dilemma. I have NO way of knowing if this is a filter, electrolytic, or what have you. I understand the top letters CP-C. They're what you set your multi meter to (if you have that type of capacitor in circuit multi meter, which I don't). I also understand it is a 400 volt before it blows up cap. I also get the 0.02 as a measure, but here is where I start to become a little too dumb for my own good. I know there are picofarads, microfarads, what have you, and all the reading I've been doing has just confused me more than I can say. Do I read this as simple microfarads? If so, how do I shop for a new cap that will do the job? I'm not sure if this cap is polarized, but it has a tiny dot next to the <JB> . which I assume is the manufacturer code. that . on the right side means? To me, it could indicate that the positive pole is to the right. Am I reading it correctly? I have a few of these motors, and a foot pedal that all need to be recapped, but I want to be certain I buy the correct capacitors for the job.

Can anyone please explain to me what I need to be looking for? I know eBay sells a lot of garbage caps, resistors, what have you, and I want to be certain that whatever I install in these motors/foot pedal(s) is going to last awhile as disassembling these motors is...problematic at best.

Thank you so much for reading. Hope someone can help. P.S. This is all the writing on this capacitor. There is nothing but blue wrapping behind and underneath. capacitor.jpg
 

Pyrex

Joined Feb 16, 2022
267
It's a film capacitor , 0.02 uF microfarads ( uF) +/-20% , 400V. You can buy a capacitor rated to 630V, for reliability
 

Thread Starter

Da Taz

Joined Jan 31, 2024
7
It's a film capacitor , 0.02 uF microfarads ( uF) +/-20% , 400V. You can buy a capacitor rated to 630V, for reliability
Thank you so much! How did you know what the rating was, if you don't mind my asking? I looked under rocks to try and verify what it was, and the type? Just know how?
 

LowQCab

Joined Nov 6, 2012
4,075
The likelihood that that Capacitor is bad is slim to none.

Don't bother with replacing it unless You definitely notice
RF-Hash-interference getting into some other Electronic-Device in the house.
.
.
.
 

Thread Starter

Da Taz

Joined Jan 31, 2024
7
The likelihood that that Capacitor is bad is slim to none.

Don't bother with replacing it unless You definitely notice
RF-Hash-interference getting into some other Electronic-Device in the house.
.
.
.
I've read that these caps last a lot of hours. However, one one of the machines I'm working on, the motor runs at one constant speed on an electronic pedal, and I noted that when I swapped in a resistor carbon disc pedal that it did what it was supposed to do, but if I gunned the pedal at startup, the machine just took off. That tells me that cap is likely out of tolerance or just plain dead. That electronic pedal...I'm pretty sure a diode as well as the capacitor are both cooked. It worked when it first hit my bench, and then it just suddenly punked out. Pedal is from the 1970's, early electronic setup.
 

Thread Starter

Da Taz

Joined Jan 31, 2024
7
The likelihood that that Capacitor is bad is slim to none.

Don't bother with replacing it unless You definitely notice
RF-Hash-interference getting into some other Electronic-Device in the house.

I have dirty power in my house. I've bought filters which helped a bit, but with or without a sewing machine present, it isn't going to make it any better or worse. I think that these "filtering" caps that this would have been a thing back when tubes were just being phased out for solid state, and things like televisions buzzed like a hornet's nest whenever lettering was on the screen. Modern machines are a whole different animal (and often not in a good way), but they're docile when running a circuit through the home's power grid. I think polarized plugs fixed a whole lot of that issue up.
 

Thread Starter

Da Taz

Joined Jan 31, 2024
7
It's a film capacitor , 0.02 uF microfarads ( uF) +/-20% , 400V. You can buy a capacitor rated to 630V, for reliability

@Pyrex

So, would an orange drop Mylar radial cap do the job? It's less voltage, only 600, but that's still 200 above the current max on this cap.
 

LowQCab

Joined Nov 6, 2012
4,075
"Electronics" in the '70's,
on a "Home-Appliance",
means only one thing, a Triac-Light-Dimmer-Circuit.
And, they are hideously NOISY.

But You still shouldn't have any need to replace the Capacitor.

If You want to make a performance improvement, ( and reduce Noise at the same time ),
create a Current-Regulating DC-Motor-Controller using the original Foot-Pedal.
Or,
the cheaper alternative,
is to just add a large Inductor in series with the Motor.
.
.
.
 

Pyrex

Joined Feb 16, 2022
267
Thank you so much! How did you know what the rating was, if you don't mind my asking? I looked under rocks to try and verify what it was, and the type? Just know how?
It's simple. 0.02 is capacity, it can't be picofarads in such a housing :), so it's microfarads. "M" means tolerance, 20 percent. 400 means voltage rating.
And yes, you can use a 600V capacitor.
I'm a little surprised, where you found such a capacitor, rated to 600V, not to 630V. Such a marking was used decades ago. Or, it is suited for a military equipment, their marking is little different
 

Thread Starter

Da Taz

Joined Jan 31, 2024
7
It's simple. 0.02 is capacity, it can't be picofarads in such a housing :), so it's microfarads. "M" means tolerance, 20 percent. 400 means voltage rating.
And yes, you can use a 600V capacitor.
I'm a little surprised, where you found such a capacitor, rated to 600V, not to 630V. Such a marking was used decades ago. Or, it is suited for a military equipment, their marking is little different
When I typed in your rating, one of the first ones to come up was the orange drop. https://www.rpelectronics.com/my-0-002-2-0-002uf-600v-radial-mylar-film-capacitor.html
 

Dodgydave

Joined Jun 22, 2012
11,304
20nF is the same as 0.02uF, just get one 450/630 V rated.

It looks like the Capacitor is across the brushes for suppression of spikes.
 
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Thread Starter

Da Taz

Joined Jan 31, 2024
7
20nF is the same as 0.02uF, just get one 450/630 V rated.

It looks like the Capacitor is across the brushes for suppression of spikes.
That is precisely it's purpose. It's "supposed" to filter out line noise, but honestly, that is not even a thing anymore. The one I need to replace is gone, think the faulty pedal that worked with it kind of caused something to zap and take the old cap down. Machine will run just fine without it, but that surge protection from the pedal is no longer there, which is why I want to replace it. Pedal needs servicing too, going to tear into it today, de-solder the capacitor after I test the circuits to see if anything else has gone south. I know a diode needs to be changed out.
 

MaxHeadRoom

Joined Jul 18, 2013
28,696
then there's this lovely little "noise reduction" capacitor that I believe is a "start/run" cap that keeps the machine from surging when you hit the machine's pedal. I've heard it called other things but its purpose is to filter out noise so that outside electronics don't pick up noise from the machine's circuit being connected to the house. I guess once upon a time that was a thing. But I digress. The main reason it is in circuit with the motor is to keep the pedal from sending too much voltage through the brushes when the motor first engages.
It is just a suppression device, it does very little for the Machine itself.
No such thing as a "start/run cap" on a DC brushed motor.

the machine just took off. That tells me that cap is likely out of tolerance or just plain dead.
Not sure how you came up with that?
 
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