Help wanted in sourcing sewing machine motor capacitor

[egaParticipant @ega]

After scanning the long list of topics I have opted for this one.

I decided I should either scrap my old Jones VX561 domestic sewing machine or replace the motor, which appeared to have failed. However, dismantling the “three prong socket” into which the power lead is plugged revealed an apparently burnt out capacitor; the separately located motor seems itself to run OK when connected directly ie without the capacitor.

I assume that the capacitor is either for starting and/or running the motor and nothing to do with the built-in machine light.

The capacitor is marked "nichicon JAPAN" and is rated at 0.05 uF 250 VAC. Being situated inside the socket on the machine, it needs to be no larger than the existing at about 1" long by 1/2" diameter.

I have tried in vain to locate a suitable replacement and am wondering whether the technology has moved on to the point where such capacitors are no longer available (my electrical knowledge is minimal).

Can anyone suggest a source for a replacement, please?

[egaParticipant @ega]

[Brian WoodParticipant @brianwood45127]

Ega,

Radio Spares used to be a fertile source of capacitors of all kinds, it may still be for all I know. Farnell might also be worth checking.

Regards

Brian

[Neil WyattModerator @neilwyatt]

It is probably an interference suppression capacitor, or a capacitor resistor combination.

If so it isn't essential unless you cause problems for things like WIFI.

Google will find you lots of alternatives, the value is unlikely to be critical.

Neil

[John RuddParticipant @johnrudd16576]

47nF will be the preferred value in todays electronics world…Ensure that the capacitor is an X rated type too….( nothing to do with adult movies..)

ESR electronics list one for 19p that is suitable…..at the bottom of the page

https://www.esr.co.uk/components/products/frame-capacitors.htm

Edited By John Rudd on 03/10/2018 16:30:12

[John RuddParticipant @johnrudd16576]

Wrong post

Edited By John Rudd on 03/10/2018 16:29:53

[SillyOldDufferModerator @sillyoldduffer]

Sounds like a suppressor capacitor rather than a Run or Start type. It's to stop radio and TV interference. Only the VAC rating is critical (at least 250VAC and X-rated), otherwise any value between 0.15uF and 0.022uF should do. These days values are often expressed in nanofarads rather than microfarads ie 0.1uF is also known as 100nF.

Rapid will sell you a pack of ten 100nF for a couple of quid. Farnell, Radiospares should also sell them. They don't seem widely available on the hobby component sites, probably because hobbyists rarely mess with mains voltages.

Dave

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 03/10/2018 16:35:31:

Sounds like a suppressor capacitor rather than a Run or Start type. It's to stop radio and TV interference. Only the VAC rating is critical (at least 250VAC and X-rated), otherwise any value between 0.15uF and 0.022uF should do. These days values are often expressed in nanofarads rather than microfarads ie 0.1uF is also known as 100nF.

Rapid will sell you a pack of ten 100nF for a couple of quid. Farnell, Radiospares should also sell them. They don't seem widely available on the hobby component sites, probably because hobbyists rarely mess with mains voltages.

Dave

If they go direct across the mains input they usually have a 100R resistor built in.

[egaParticipant @ega]

Brian Wood and Neil Wyatt:

Many thanks for the instant replies.

I had previously looked at both the RS and Farnell websites and had no joy. It may well be that a more savvy searcher would get a result. One problem is not knowing the function of the capacitor; normal motor capacitors are, of course, a good deal more bulky than the one in question.

I did wonder about its precise function. My conclusion was based on the idea that these rather puny motors (60W in the present case) have to start under load. I will, however, as a temporary expedient, try to see whether the machine, including the speed control, will run without the capacitor.

In the meantime, does any other knowledgeable member confirm Neil's suggestion?

[egaParticipant @ega]

John Rudd and SOD:

No sooner asked than answered – thank you!

Neil: so far as I could see when dismantling, the capacitor is wired across the neutral lead to the motor and the live lead to the lamp but this does not take into account what goes on in the foot switch.

Thanks again for the helpful suggestions which I will pursue.

Incidentally – sign of the times – the Jones was made in Taiwan and my Singer replacement is a Brazilian!

Edited By ega on 03/10/2018 16:58:58

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 03/10/2018 16:44:16:

Posted by SillyOldDuffer on 03/10/2018 16:35:31:

…

Dave

If they go direct across the mains input they usually have a 100R resistor built in.

Never heard that before Neil. Doesn't sound a daft thing to do on a suppressor, but its not mentioned in various X spec sheets I looked at eg this Vishay example . How common is a built in resistor?

I've put 100W of RF through one to feed a transmit antenna – surely a 100 ohm resistor would have smoked? Perhaps I just got lucky!

Dave

[John HaineParticipant @johnhaine32865]

I've got a pile of these in a drawer somewhere – I'll send you one for free if you're in the UK and drop a couple of squids in a charity box. PM me address.

[egaParticipant @ega]

John Haine:

Many thanks; I have sent you a PM.

Someone asked for a photo of the capacitor and I have put one in my Miscellaneous album (at the end).

[Robert Atkinson 2Participant @robertatkinson2]

The component Neil mentioned is called a Snubber. It limits the rate of change of voltage across a contact (or electronic switch like an SCR). While not a EMI suppressor per se, reducing the rate of change reduces the EMI.

Robert G8RPI.

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 03/10/2018 17:04:48:

Posted by Neil Wyatt on 03/10/2018 16:44:16:

Posted by SillyOldDuffer on 03/10/2018 16:35:31:

…

Dave

If they go direct across the mains input they usually have a 100R resistor built in.

Never heard that before Neil. Doesn't sound a daft thing to do on a suppressor, but its not mentioned in various X spec sheets I looked at eg this Vishay example . How common is a built in resistor?

I've put 100W of RF through one to feed a transmit antenna – surely a 100 ohm resistor would have smoked? Perhaps I just got lucky!

Dave

Note circuit diagram and wording "RC-UNIT"

[Howard LewisParticipant @howardlewis46836]

If you want a motor, I have one that you can have for free.

I am in East Anglia, just off the A47, if you or anyone else, wants to collect, (PM me).

Howard

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 03/10/2018 21:11:55:

Posted by SillyOldDuffer on 03/10/2018 17:04:48:

Posted by Neil Wyatt on 03/10/2018 16:44:16:

Posted by SillyOldDuffer on 03/10/2018 16:35:31:

…

Dave

If they go direct across the mains input they usually have a 100R resistor built in.

Never heard that before Neil. Doesn't sound a daft thing to do on a suppressor, but its not mentioned in various X spec sheets I looked at eg this Vishay example . How common is a built in resistor?

I've put 100W of RF through one to feed a transmit antenna – surely a 100 ohm resistor would have smoked? Perhaps I just got lucky!

Dave

Note circuit diagram and wording "RC-UNIT"

Well I never – it's a single component. All these years I've messed with electronics and never realised you could get RC in the same package. Begs the question though, should ega fit a plain suppression capacitor or a snubber to his motor? My guess : it doesn't matter much!

Dave

[Robert Atkinson 2Participant @robertatkinson2]

If the OP's component is connected across the mains (L & N) then it should be a class X capacitor (this is what I think it is). If it's connected across the switch a snubber would be more appropriate.

Robert.

[egaParticipant @ega]

Howard Lewis:

Many thanks for the offer (I saw your old post and wondered if you had found a taker). John Haine, however, is kindly sending me a capacitor which I hope will solve my problem.

As a matter of interest, does your motor have an integral socket? I actually have a spare motor with this feature bought with GHT's UPT in mind but have never fitted it. Unfortunately, the Jones has a separate socket and fitting the spare would involve undesirable complication so I am hoping that the capacitor is all that is required.

Neil Wyatt et al:

As to snubbers, I am "none the wiser but so much better informed" and, as I say, hoping to get by with the capacitor!

[Howard LewisParticipant @howardlewis46836]

Hi ega.

Glad that you are, or soon will be, up and running. Nice to know that a poster's problem has come to a good conclusion.

My motor is still hard wired to the pedal. Came from stripping down a redundant machine that I was given, and lacked the heart to dump it!

Would be happy if it went somewhere it was useful rather than into a skip.

Howard

[egaParticipant @ega]

Howard Lewis:

Interesting that your motor is hard wired to the pedal rather than being connected via a socket. Incidentally, there was an earlier thread with suggestions for re-purposing the mechanical components of an old machine.

I will post the result of trying the replacement capacitor in due course and in the meantime will be taking in your article in the current MEW.

[egaParticipant @ega]

I am happy to report that, thanks to the helpful replies to my post and, in particular, to John Haine who very kindly sent me a replacement capacitor, the Jones is now working.

I am, therefore, confident that the problem was a failed capacitor; is there, I wonder, an accepted and accessible way of testing these? My initial, unscientific, diagnosis was based on smell and the burnt-looking spot on the casing of the original device.

[John HaineParticipant @johnhaine32865]

Glad you're sorted now. The problem with testing them is that the capacitor is in parallel with the motor, so any test based on looking at the input terminals, for example with a test meter, only really sees the motor since it has a rather low impedance while the capacitor to all intents and purposes is an open circuit except to RF interference. A "loud brown smell" is probably the best diagnosis!  Suppressor capacitors seldom go, and when they do are self destructive so it's obvious.

Edited By John Haine on 06/10/2018 16:56:20

[egaParticipant @ega]

The mention of RF interference suggests the "method" of turning on the radio and noting the quality of the reception!

I remember being unpopular a long time ago when running a pre-war Austin Seven with unsuppressed plug leads.

[SillyOldDufferModerator @sillyoldduffer]

Testing capacitors used to require ouch expensive specialised equipment, but as with other electronics, prices have dropped amazingly. Not the best test kit in the world but this £15 multimeter can measure capacitance. Plenty of other examples on the web, also more sophisticated boxes that can test inductance, resistance, capacitance, ESR and other goodies.

Even with fancy kit, exactly as John explains, you still have to disconnect one lead to make sure the measurement isn't wrecked by whatever else the capacitor is connected to.

Dave

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