Myford two speed motor wiring

Can anyone help with the wiring of a Crompton two speed motor as fitted to a Myford TriLeva. A friend has the machine and it was delivered with the switch gear removed and just the motor tails hanging out. The motor plate says it is a 2 speed, 1440/2800 RPM single phase motor and it has a single capacitor mounted on the side, but the associated (and incomplete) slip of paper found in the connection box does not match either the motor iteslf nor the remains of the switchgear. FWIW the motor tails from within the guts are: Red, Red/Bk, R/Wh, Wh, Bk, Yellow, Yellow/White(or orange)

All suggestions gratefully received Richard

Reply to
Richard Shute
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I'd have expected 8-10 wires (assuming a fully reversible motor) but presumably some have been linked inside which will make it more interesting!

It will be a case of carefully measuring resistances between all wires to identify 4 windings and a capacitance meter to find the capacitor. There will be two run and two start and the capacitor which will almost certainly be permanently connected to the centrifugal switch.

Using something like an electric fire element in series you can apply mains to each winding in turn and spin the motor by hand in either direction. It will run faster with two of the windings than the others so you can see which are the two pole windings and which are the four pole ones. The run windings are likely to be the lower resistance of each of the pairs.

Then wire up and test your theory!! Always earth the motor body and have a supply of fuses on hand!!

It will be fun if nothing else!


PS Some back of envelope doodles have come up with 5, 6 8 and 10 wire topologies but not 7 ! I'll be very interested in your conclusions

Reply to
Bob Minchin

Bob, thanks for that. It gives me some idea of what to expect. I am familiar with pole changing 3~ motors, but not had to deal with a 1~ one before.

Interestingly, I did find this query which also noted a 7 wiire motor:

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unfortunately there seem to have been no informed replies.

I'll post an update when I have some more details.


Reply to
Richard Shute

I can't even recall me making that request but it was nearly 10 years ago. I get about 5-6 motor queries a week so hardly surprising I forget some!!


Reply to
Bob Minchin

Knowing sod all about wiring motors, only mending them it came to me that of the colours stated there look to be three pairs if you match a colour up to a stripe and then an odd black.

Could these three 'coils' be high, low and a common starting coil with the black being one side of the switch ?

If what I say makes no sense then tell me to sod off and I'll go sulk for 8 or 9 seconds.

John S.

Reply to
John S

John, I strongly suspect you are right, but the motor isn't within arms reach for me to check and I was hoping that something as common as a Myford would have a well documented answer.

Chees Richard

Reply to
Richard Shute

Have you tried calling Crompton as I remember the same sort of thing being asked before the internet and they could sometimes be of help.

Reply to
David Billington

I just happen to have the "Brook Crompton Parkinson" "Little Red Book" discussing the Installation and maintenance of motors. Unfortunately nowhere can I find a diagram for a two speed single phase motor. However Yellow and blue tend to be the colours for "Start" windings and red and black for "Run" windings. White is often used for switch wiring. As has been discussed you need to check resistances with a good meter. Has it got a switch, is there only one capacitor?

-- Richard

Reply to
Richard Edwards

Hi Richard & Dave I did contact Crompton, but unfortunately the relevant division closed last year and they have passed Service to some other firm whom I called afterwards. Ssadly they were completely unaware of any technical details. So much for 'Service'.

I have a BC motor on one of my lathes and I agree with the comment about wire colours and was going to take a stab in the dark based on that, but jumping from 4 wires to 7 leaves a fair bit to faith and chance so I thought a post here would help.

At present the motor has one cap., but I strongly suspect it should have two. This for two reasons: there is an incomplete slip of paper with some wiring hints stuffed in the connection box from which I deduce that two cap's are expected and secondly there is the old ref. above from Bob who encountered the same problem and the motor he was working on then had two caps.

As yet I have not had the chance to get accurate resistance measurements done and it is complicated further by the fact that the motor is remote from me, I can't just nip round and check. However the young lady with the machine is pretty savvy so with a bit of guidance she should be able to get the readings.

Thanks to all so far, I'll update when I have something useful Richard

Reply to
Richard Shute

7 wires when I would expect 6. Perhaps one is a frame ground ?. 2 of the wires will be the starting winding, which may be of smaller gauge wire than the run windings and which is normally reversed, in series with the starting cap, to get f / r rotation. May be much higher resistance than the run winding, but be carefull not to run the mains direct to this, as it may cook the winding.

This leaves 4, with two each for the high and low speeds, though they may be interconnected in some way to save wire.

Perhaps the best way to find out which is which is to connect 110v to each run winding in turn and manually spin up with string around the shaft to find out which is the high speed winding. It should run in either direction with the start winding disconnected.

Somewhere, I have an old P Marshall book on rewinding motors which may have info on winding configuration. Will check...



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