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ML7 Motor - what would you do?

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Phil Whitley23/01/2015 23:58:45
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1533 forum posts
147 photos

Hi Peter, Your motor is almost definitely star connected, the box on the label under the frequency should have a symbol, or S or D in it, but as far as I can see it is not marked. the star point will be on the winding itself where the other three ends of the coils will be soldered together and insulated. If you want to run this motor in delta, you will have to find this connection, unsolder the ends, solder a tail wire onto each one and bring them into the terminal box.Test with a multimeter to find the three coils. designate the three connections you already have as A1, B1 and C1, designate the other ends of the respective coils A2, B2 and C2. Connect A1 to B2, B1 to C2 and C1 to A2. put one phase of the supply to each junction. If the motor runs smoothly and quietly, but the wrong way, reverse any two of the incoming supply phases. If it runs slowly and growls, swap over the A1 and A2 connections. if it is still the same, put the A connections back where they were and swap the B connections.if no better,swap the B connections back, and continue with the C connections , and you will be sorted!

Phil

Peter Bond24/01/2015 09:42:24
65 forum posts
8 photos

Hi Phil -

I suspect you're right on the connections, particularly given the age of it. Reading the books, I'm intrigued as to how it is dual voltage without any obvious wiring links. I note that some of the VFD manuals advocate delta connection only, whereas others don't mention it at all.

The rewiring sounds worse in description than it is likely to be in practice!

Phil Whitley24/01/2015 10:56:04
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1533 forum posts
147 photos

Hi Peter,

The motor has been rewound at sometime in its life, the varnish on the rating plate is a dead giveaway. the motor would have been star connected for high voltage, and delta connected for low voltage. Obviously this cannot be done with only three connections available, so it looks like it has been rewound in star only configuration. strip it down and see if you can find the other connections.

Phil.

Peter Bond25/01/2015 16:17:35
65 forum posts
8 photos

Interesting - why is it a dead giveaway? The thing has been resprayed at some point too - assuming it wasn't standard practice to paint the motors after assembly.

Windings exposed

There's a nice load of resin over the insulation, so it's going to be entertaining trying to find the termination...

Mike Poole25/01/2015 16:24:42
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3676 forum posts
82 photos

I think most rewind shops paint motors after assembly, it would be a nightmare to mask and spray before.

Mike

Phil Whitley25/01/2015 16:47:05
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1533 forum posts
147 photos

Hi Peter, they usually dip the whole stator in varnish, agitate it, wait till the air bubbles stop rising, then lift it out, let it drain, and when the varnish has "tacked off" they bake it in a stoving oven. Rewinds nearly always come back with a nicely varnished rating plate.

Phil

Phil Whitley25/01/2015 16:49:37
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1533 forum posts
147 photos

PS, have you looked at the other end of the motor, it would be unusual for the connections to be there, but you never know.

Phil;

Peter Bond07/02/2015 11:03:05
65 forum posts
8 photos

Sitrep... I can't seem to locate the ends of the tails, and the varnish on the tape wrap is sufficiently tough to get through that I'm a wee bit bothered about damaging the wiring as I do so. I might try a heat gun and see if it makes it any more biddable.

Les Jones 107/02/2015 12:06:26
2292 forum posts
159 photos

Hi Peter,
I think you should try to find someone more familiar with motors to have a look at it to see if they can locate the star point. As you do not have a profile no one on here knows if they are close enough to offer help. You could try a local model engineering club or pay a motor rewind company to do it for you. If you live close enough to me I am prepared to have alook at it.

Les.

Peter Bond07/02/2015 13:48:04
65 forum posts
8 photos

While that is a suggestion with some merit, if I have to admit defeat and take it to a motor winder then I may as well buy a new motor, it'll probably be more cost effective. Fundamentally, all this is is a bundle of wires - I *should* be able to find the end!

I've been remiss on the profile; mea culpa - now updated. I'm in Romsey and I don't know of any nearby model eng. clubs.

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