Rewiring old 3 phase motor for low voltage

Gallery, Projects and General > How do I??

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loply:
Thanks for the help folks.

Armed with the entirely safe combination of an undue sense of confidence, a small pair of scissors and a little bit of knowledge, I set about chopping up a 50 year old motor.

After some searching I found what I presume is the star point, as it's the only bit that looks like a star.

And after removing a battery from a less worthy device to power my multimeter, I can confirm that each point of the star, when separated, connects only to one of the original screw terminals.

Now the only thing I don't know is how to reconnect them. I've read a few pages but they seem to conflict with each other. Can I just randomly label the pairs as U/V/W as I see fit, then connect them in Delta as per usual?

Cheers,
Rich

lordedmond:
yes you can ,but the rotation would be random , if its wrong just swap two power leads and you will be fine

make sure you clean the enamel off completely ( scraping is best )

I use to use silberloy barraging rod ( no flux required and above all no cleaning of the enamel

good luck and dont forget to tie the wires in tight and put some varnish on them ( poly is ok for this its to stop the wire rubbing together)

long time ago ( during my apprenticeship ) I did stator and armature winding

Stuart

BillTodd:
Well done :thumbup: Glad it went well for you :)

--- Quote ---Can I just randomly label the pairs as U/V/W as I see fit, then connect them in Delta as per usual?
--- End quote ---

The original wires should identify the phases so just wire and label the tails as U2,V2 & W2.

If you connect

U2 - V1
V2 - W1
W2 -U1

It should rotate as expected.

Bill

loply:
Bill, Stuart - Thanks to both of you for the help.

I stripped the varnish from the 'star' leads and soldered on some new extensions, then hooked up this 3 point junction box bringing all 6 ends to the electrical access point and wiring it into Delta at the same time:

Slightly non-standard cable colours admittedly, but I got it sealed back up and popped a new grommet and armoured cable on for good measure:

One quick hoist with the engine crane later and I ground my first parts - the jaws of this old WW2 Paramo vice (which were too bad to get completely flat!) and this triangular chuck adapter plate for my RT. Motor ran perfectly and the finish was impressive for my first shot with an unidentified wheel!

Thanks folks,
Rich

David Jupp:
Great - I have a similar original motor for my Smart & Brown lathe (in my case a 6 pole, 970 rpm) - every time I've looked so far I've chickened out from digging to find the star point - I have a modern 4 pole motor in place temporarily.

I really must have another go at finding the star point - no obvious joints that 3 wires head into.... it would be really good to get the speeds back to original plus have VFD.

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