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Posted to rec.crafts.metalworking
Grant Erwin
 
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Default Will this work? VFD question. Silly.

Eric R Snow wrote:

Just wondering. I'm not gonna try it out. No sense in it. But here it
is: Three 240 volt single phase motors are wired together in delta,
the shafts are connected together in line, and the starting windings
are disconnected. If connected to a VFD, or any three phase source for
that matter, will they spin up? Will they maybe need to be rotated at
assembly 120 degrees to each other? I think it will work. Just idle
curiosity. We all know how dangerous that is.
Thanks,
Eric


Basically you have L1, L2, L3 each 120 degrees apart. If you feed motor 1 L1-L2
(which would be 208 volts) and motor 2 L2-L3 and motor 3 L1-L3 then if they run
on 208 volts they should all run OK but with no start windings they wouldn't
start, as there is no rotating magnetic field when connected to a single phase.

My intuition is they'd just sit there and hum, but if you didn't disconnect the
start windings they would all work OK.

The load would be balanced as long as each motor was loaded the same. Only way
to do that would be to have 3 208-230V motors each with shafts at both ends, and
use shaft couplers e.g. Lovejoy ..

GWE