Start capacitor failure?

[Chipmaster]

Over the last couple of weeks my Colchester Chipmaster motor has been increasingly reluctant to start. I have been able to tug the drive belt to encourage it but it refused to go yesterday and just growled at me until the thermal cut out - cut out. This appears to be symptomatic of a failed capacitor.

The motor on a Chipmaster is difficult to remove slung upside down beneath the Kopp Variator.

IMG_3494 (2) by Andy, on Flickr

IMG_3498 (2) by Andy, on Flickr

I bought the Brook Crompton 2.2kw single phase motor new 31 years ago just after I'd bought the lathe but couldn't afford a phase converter. Fitting it was a straight swap for the three phase motor which I still have, at the time I didn't imagine acquiring more machinery and a Transwave Converter as has happened as my salary increased.
It took some mauling to remove the variator and motor assembly, I was fitter then and don't relish having to repeat the exercise. By the way there is only this single capacitor on the motor.

So, I managed to remove the just the capacitor and felt quite pleased. However, The large clips that held the capacitor plus the manufacturer's paint job almost obliterated the specification on the sticker attached to the capacitor.

I think it reads 160 micro farad and a couple of sources reckon that is likely, can any MEM members confirm or suggest the spec for the start capacitor?

The capacitor 130mm long x 50mm diameter.
IMG_3496 (2) by Andy, on Flickr

A couple of zoomed in shots of the label,

 IMG_3495 (3) by Andy, on Flickr

 IMG_3497 (2) by Andy, on Flickr

The start capacitors aren't expensive and I assume the spec wouldn't be precise so reckon if I fit a new capacitor and the motor starts quickly that's ok. If it doesn't start quickly I turn it off before the capacitor explodes!

Andy

[Jo]

Tugging the belt 

Great news surgery has moved on greatly over the years  . I think Stuart had his finger go under a belt round a pulley he can give you the gory details   



Any part of the series circuit could have done what you describe. Have a measure of the windings while the caps off. On a 3HP motor it may well be a 160 UF Cap.

..... I hate to think how big the spike is that goes down the mains when that starts. Does it cause interference 

Jo

[Admiral_dk]

I read it as : 160µF -0/+25% (tolerance -> 160-200µF), 250-275Vac. 50-60Hz.

A new cap should be a cheap solution - and a VFD combined with the old 3 phase, would be the fancy solution.

I hope that you solve this to your satisfaction 

Per

[Chipmaster]

Ah yes I agree Jo, I should add that the motor wasn't turned on when I tugged the belt, I was only moving it a few inches before closing the cover and trying to start the motor again. The Chipmaster has a safety switch (plunger type) that disconnects the power when the large fibre glass end cover that protects all the belts and change gears is open. 

I haven't been aware of my motor causing interference, it used to dim the lights momentarily when I started it but it didn't cause any problems with computers. That was in a 1930's house I lived in until 2003, perhaps the electricity cabling to the house wasn't up to current standards. Where I live now in a thirty year old house there's no problem at all, my wife hasn't noticed the lights dimming.

So you think 160uf is likely, thanks.

Andy

[Chipmaster]

Thanks Per I feel I can order a 160-200µF tomorrow and be confident of a satisfactory result.

Andy

[MJM460]

Hi Chipmaster, my mill was a bit slow on starting particularly on high speed.  I replaced the capacitors after a little research and solved the problem very nicely.  My lathe is starting to show similar problems, but like yours, a pain to get at.  But that is next on the list when the weather warms up a bit.  I wrote it up recently on the tooling and machines board.  It does not seem like an uncommon problem, and replacing the capacitors seems the right place to start.

Will be interested to hear how it goes when your new capacitor arrives.

MJM460

[Jo]

I just wandered over to Brook Crompton website. They very helpfully provide lots of useful information in their booklet on single phase motors: http://www.brookcrompton.com/upload/files/products/2227e_1phase_v1.1e.pdf

Their modern 2.2KW single phase Capacitor Start Capacitor Run motors they identify them using  20OUF start and a 20UF running capacitor. Did you check is there a running capacitor?

I went there trying to find the starting current for single phase motors. I assume you have it on a 40A ring main 

Jo

[Chipmaster]

Hello Jo,
thanks for your interest, when we moved to this house five years ago I had professionals install a new power supply taken from the meter and routed underground to a new distribution board in our detached garage. I know that the board has a 100A circuit breaker then individual mcbs for radial circuits to the lathe and phase converter, there are further ring circuits for sockets, lighting, garage doors, outside lighting etc. I don't remember the rating of the circuit breaker dedicated to the lathe, perhaps 35A but it hasn't tripped in the last five years or the previous 25yrs in other locations where it was on its own 35A supply.
My 2.2kw single phase motor definitely only has one capacitor unless another one is cunningly concealed inside the motor casing  . 

I hope to report a successful conclusion if I can fit a replacement capacitor tomorrow.

Andy

[AOG]

If you don’t see a run capacitor it may be built into your start cap. The way to tell is the number of leads on the part. If it’s 2 it’s probably a pure start capacitor. If it has 3 separate leads it’s the start/run type.

Tony

[Chipmaster]

The Chipmaster lathe motor is back to normal, a new capacitor did the trick

A local Redditch firm 'Electrical Mechanical Solutions' ( http://e-m-s.uk/index.html ) who specialise in the repairing, servicing and supplying of electric motors didn't have start capacitors in stock, they suggested I contact Rush Industrial Sales in Sandy, Bedfordshire ( https://www.rushind.com/index.html ). Here I spoke with Andre who took time to discuss the problem motor and identified the appropriate capacitor by reference to his records of backdated GEC Brook Crompton specifications. The capacitor supplied and posted.....



The new capacitor was fitted this morning and I have started the lathe many times, it's running as it should, what a relief.

I recommend Rush Industrial Sales - Andre, to MEM members for the supply of capacitors.

Thanks to Jo, Per, MGM 460 and Tony for their input and advice.

Andy

[Jo]

 

[Chipmaster]

Oh dear, back to square one the motor is playing up again after an hours use 

Time to think about putting the original three phase 3hp motor back in the lathe and buy an inverter.

Andy

[Admiral_dk]

Oh dear - that is annoying .... there must be another reason it kills the caps, but probably not worth trying to discover why, as it most likely means another motor anyway ....

[Jo]

 

Did you measure the coil winding resistance? Did you measure the old capacitor to see if it was short circuit?

The other (relatively) cheap thing that may have gone wrong is the switch  .


Was there any "odd smell" and was the motor hot? (= possible cooked winding  )

Jo

[Chipmaster]

Hi Jo,

I don’t know what the coil winding resistance should be even if I was able to measure it. The motor is in such an awkward position that it’s not possible to access particular terminals on the motor. I had to use an inspection mirror to disconnect the capacitor but I was very lucky with the connections which happened to be on the two convenient to reach posts.
I feel that if I go to the trouble of removing the motor and Kopp variator I might as well opt for putting the original dual voltage three phase motor back, dispense with the variator and use an inverter, perhaps from Transwave who are only ten miles away.
A friend had his single phase motor from his Myford lathe repaired a couple of years ago, it was quite expensive, so repairing my 3hp single phase probably won’t be worthwhile.
This is the opportunity to have a smoother and quieter three phase motor driving the lathe....so any suggestions gratefully received.

How do you power your machine tools Jo ?

Andy