Single Phase Motor 'Run' Capacitor?

Does anyone have any knowledge of "Run" Capacitors for single phase motors?

I have a little pendant drill motor that upon dismantling i discovered the capacitor inside had exploded; there was no clue to the 'value' of capacitor, at least none that was left on the remaining casing. I emailed the original manufacturer to see if they may have information in their archives (long shot as i imagine it's 30+ years old), that turned up nothing.

It is some kind of film capacitor, but unusually has 3 terminals, and I assume the motor is a PSC type motor, it has a footswitch for speed control.

Could anyone hazard a guess to what capacitor to replace it with? I don't want to damage the windings by fitting the wrong capacitor. The motor is labeled 'Deroter' and is 60 watts.

If this motor has a commutator then I think the capacitor is there for spark suppression. It is probably two caps, one connection to each brush and a common earth wire.

John

Just a Delta Capacitor probably. 3 caps.

This is the sort of thing you need but it's too large to fit in. Bottom of page.

**LINK**

There are some others in a smaller package but beware. Similar looking things are made in ratings for low voltage motors ...

Like the items at the top of the link.

Make sure you get one rated for 240VAC

Dave

Just had a sniff around ...

Probably a better bet:

http://cpc.farnell.com/evox-rifa/pzb300mc13r30/capacitor-delta-network-0-1uf-2x/dp/CA08123?in_merch=New Products

Edited By Dave Daniels on 30/03/2014 08:47:11

Edited By Dave Daniels on 30/03/2014 09:01:36

Edited By Dave Daniels on 30/03/2014 09:03:04

I f the motor has a commutator and is fitted with carbon brushes then the capacitors, as others have said, are for interference suppression and the motor should run with out them, for test perposes only !. The capacitors should be X type as the adverts says.Ted

It's a RFI suppression capacitor. Yes they do explode, When I was about 7 or 8 years old, I was tucked up in bed in my room next to the living room where mum was sewing, when there was an almighty BANG, I got up and went to see what had happened, and there was mum, still sitting in front of her Singer sewing machine, in the midst of a cloud of smoke. An hour or so later dad (a radio technician), and he declared it ok for normal use, and it was used for another 30 years, until traded in on a new machine. No RFI noted in all those years, plenty from other bits of machinery around the house. Ian S C

Ah, thanks everyone! It does have a commutator so that does seem like the correct type of capacitor. I'll buy that one that Dave Daniels linked to... It's typical, I placed an order with Farnell just yesterday, I'll have to see if they can add it to that order before they despatch it (it's £20 minimum order on card payments).

Thanks again.

Daniel ..

It's not Farnell Leeds, it's CPC-Farnell at Preston. Unless Farnell have the same item.

You have checked the dimensions to be sure it fits, I hope ?????

To be quite honest, I would do what Ian says, just remove the thing and see if it creates RFI. If not just forget it ever happened ...

Not elegant but cheap ... one of the philosophies I prefer

Dave

Edited By Dave Daniels on 30/03/2014 14:48:15

It is bigger, but it should fit. Farnell does have it, so I may as well try and add it to my order, meanwhile I'll check the RFI.

Thanks.

Daniel,

Most Farnell components are available through CPC (part of the same group) but they have no minimum order and free postage on web orders.

Neil

Just a word of warning. Got an old U/S sewing machine today, it has a Singer motor on it. I plugged in the foot control, and connected up to the mains, and the motor ran OK, and the lamp lit up. Unplug, and start to disassemble, first thing to do is disconnect the lamp so The wire can be threaded through the body of the machine, grab wire cutters, and cut the wire---- BANG, I had forgotten to discharge the suppressor capacitor on the motor, no harm done, but watch it. Ian S C

Visited my cousin this weekend, both his bandsaw and small pillar drill motors would not start without a 'flick' - pretty dangerous !! Anyway, I went down to the local motor re-wind place and bought a couple of 'motor run' caps and then all was well. Would have been cheaper by E boy, but time was of the essence. Question, why would two independent motors have their caps blown. Do caps suffer from getting cold (un-heated garage)?
BobH

Could if they were oil filled, with the cold, the oil contracted and sucked in some damp air which got in the capacitors windings. Just a posibility?

Frank

I just had a start capacitor fail on my pillar drill. It was rated at 150 micro farad but when I measured it the value had fallen to just 26 micro. I borrowed the cap from my bandsaw to get me going, it was only 100 uf but it did the job. They do dry out with age and the value will fall until the point where the motor won't start any more.

Not much use to the op but as the thread had drifted a bit I thought I would add my 2p.

David, had the same happen with my weed mulcher, 1/2 hp motor, grabbed a salvaged one from the junk box, as long as it's within about 50% +/- it should do, they are not high precision capacitors.

ian S C

Hi there, Daniel,

Have you resolved your problem with the Derotor?

I have an identical motor, complete with foot control and flexible shaft - my late wife used to use it for her hobby of glass engraving. When I tried the motor recently it tripped the domestic earth leakage trip. I have tested both the motor and the foot control unit with a Megger and I'm getting 5 Megohms from both phase and neutral to 'earth'. The brushes still have lots to go and there's no evidence of carbon dust.

I explored the maker's web-site but they seem to have migrated their 'core business'.

I'd be grateful to hear exactly what component (supplier & part number) you've used and whether it solved the problem.

Best regards,

Swarf, Mostly!

Hi there, Daniel,

Please check your PM inbox.

Best regards,

Swarf, Mostly!

Suppressor capacitor to earth can create earth leakage which would take the breaker over the edge. There could be some other leakages in your wiring even if the leakage from this motor is inadequate in itself to trip the breaker.

The motor will run without the electro magnetic interference capacitor EMI, these if I remember rightly are know as either Y type or X type. The idea is, they should never fail short circuit. Vacuum cleaners, food mixers have similar ones. These capacitors are not the same as motor start type, which are short time rate AC electrolytic. Motor run are continuously rated. and often have polyprolene or quality paper dielectric (insulation) John.