Multi speed induction motor 1

[zeusfaber]

Bit of a schoolboy question here - but one that's outside my normal territory.

Somebody's asked me to look at a three-speed induction motor that's been sitting separately from its partner machine tool for long enough that the identity of the nine terminals on top of the machine has been lost.

After a bit of nosing around, I'm pretty happy that we've got a 2/4 pole Dahlander winding, along with a dedicated 8 pole winding for low speed operation.

My instinct is to assume that there's bound to be a little bit of residual magnetism in the rotor allowing me to use it as a not-very-excited-at-all synchronous alternator, spin it round with an electric drill and put a scope across the various terminals and confirm that I see sine waves at the appropriate frequencies to check that I haven't misidentified anything before risking connecting it to a supply that's powerful enough to let the smoke out.

Is that a pretty normal sort of test? Is it likely to work? Is there anything I particularly need to beware of?

Thanks.

A.

 

[Skogsgurra]

It is a very good way to identify windings. It may be better to use a recorder to get a picture on a slip of paper. Running with a drill usually causes so much jitter that you eventually give the whole thing up. A "stationary" recording on paper is much better, you can make notes on it and figure what is what.

You can easily magnetize the rotor by using a 12 V car battery. Doesn't matter how you connect - the rotor gets magnetized whetever you do. Make sure to just flash the stator, the DC may cause overload. One or two seconds is all you need to build up a decent field.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[zeusfaber]

Gunnar,

Thanks for that - two really useful points.

May be a few days before I get a chance to put it into practice.

A.