Motor starting capacitor - Axminster M900

[Glynne]

After a blue flash, bang and tripping the power in both workshop & house, the goo coming from the capacitor housing was a bit of a giveaway as to what might be the cause.
The capacitors was: -

SSEC Motor Starting Capacitor
cap 200 mfd
wv 250 vac

I've tried googling for a direct replacement but can't immediately find one.
I'm assuming another starting capacitor of the same specification will be suitable but thought I'd better ask those more knowledgable?
Any suggestions as to a supplier would be very welcome to please.
Thanks.

 

[CHJ]

That capacitor figure does not look right,

Is it a replacement fitted by someone else.

It should be 300-400 volt working. and value in the order of 10's of Mfd. and should be RUN Rated.
Start rated will overheat if used continually connected.

Something like this is what was fitted to my Perform version of the lathe.
http://www.ebay.co.uk/itm/20uF-Motor-Ru ... SA:GB:1123

 

[Glynne]

Thanks for the reply Chas.
I've had the lathe for ~ 15 years, bought from Derek Pyatt as an ex-demo so I doubt that it has been replaced.
I've never had any problems in the past so it would seem to be compatible or I've been lucky.
I'm not sure what motor the Perform has but mine is a 1/2 HP 5 Amp if that makes any difference.

 

[sunnybob]

http://www.motors-direct.co.uk/index.ph ... uct_id=445
200 is right according to the research I've just done.

 

[CHJ]

All the machines I've come across from that series of lathes branded by various retailers use a simple aluminium framed motor using a Run capacitor that stays in line at all times (provides start in correct direction and a pseudo 3rd phase to increase torque whilst running)

If the motor is using a start capacitor then it must have some form of switching fitted, either a centrifugal switch in the motor or a sophisticated starter unit, I can't see a Axminster M900 machine having such.

Mfd's in the 100's I would expect to see in 3-5 HP systems not 1/2HP

Do you have an image of the motor on the lathe?

Does the machine basically look like this.

http://www.axminster.co.uk/media/downlo ... manual.pdf

 

[sunnybob]

This video explains a lot.
https://www.youtube.com/watch?v=OMd9QkinXz4

 

[CHJ]

Glynne , are you sure it is 200Mfd, and not 20.0 Mfd.

I would not fit a 240 volt rated device as replacement.

The 240 volt mains is an RMS voltage so the voltage spike/highest value the component sees is much higher and needs internal insulation that will stand this.

 

[Glynne]

Thanks for the replies guys, I really appreciate your time.
Photos as requested: -

Motor assembly obviously has the cover removed (black is from ebonising spray!).
As I said, I've had the lathe for about 15 years and even if the supplier (Derek Pyatt Woodworking) had replaced the capacitor which I very much doubt, it has lasted me this long without any problem.
You can't really see it on this photo, but there is a spring assembly within the motor that looks very much like it could be a centrifugal mechanism.
As you can see the lathe is similar to the manual but appears to be a more modern version.
After the original "bang" and I'd reset the electrics, the lathe would still run only it sounded considerably different. After a second bang (but no electrics trip), I decided discretion was the better part of valour and hence my post.
Thanks again.

 

[CHJ]

OK that looks like a much earlier version with a Centrifugal starter switch, In which case the capacitor size will be more generous and start rated.

Do you remember that the motor generated a reasonably loud click or rubbing noise whilst it slowed down, (switch closing)

It could be that the centrifugal switch is not working correctly and has not opened up the contacts and hence subjected the capacitor to a prolonged current draw which cooked it.

You need to take the cooling fan off and inspect the switch, you should be able to open up the contacts by pulling the spring held weights apart, check that the contacts are not welded together, if they look pitted clean them up with some fine glass paper, not emery paper.

All with machine disconnected from mains, not just switched off of course.



To test motor, cut off damaged capacitor leaving as long as possible leads, insulate the ends.
Apply power to the motor and if it does not move and spin up slowly straight away (don't leave it in condition long, it will overheat) with care spin the motor or lathe spindle by hand and see if it runs.

If it does then fit new capacitor, the 200Mfd figure is not critical. The nearer the more start toque.

 

[Glynne]

Thanks Chas.
Followed your instructions and: -

Pulling the weights apart, the assembly slides forward and a thin metal plate contacts the terminal behind the bent bracket above the spring. I"m guessing this is the electrical contact but I would struggle to see if it's pitted or not.
Capacitors removed (screw fittings) and wires insulated, the lathe starts up straight away and the centrifugal switch seems to work fine.
So I think I'll order a new capacitor and see how it goes.

 

[CHJ]

That looks remarkably clean and tidy for its age, guess it's just a case of old age on the capacitor, once a small hole appears in the internal insulation they go down catastrophically.

 

[NazNomad]

... and let's not even get started with the old µF / MFD debate.

 

[Glynne]

Thanks Chas.
I've sourced and fitted a new capacitor (with a bit of Heath Robinson engineering as I couldn't match the physical size of the old one) and the lathe works fine. When I say fine, I've now noticed it is incredibly noisy and so I'll start a new thread on this!
Thanks for your help again.