----------- Actually it won't- except for losses - the power is supplied electrically, not mechanically - >
-------------------- That would require a bit of calculation but the "supply" machine must be able to handle its own real and reactive needs, as well as those of the load motor from the single phase line without smelling funny. It will not have balanced currents. If "large" with respect to the load, it is not a problem. If you have access to cheap, large 3 phase motors it is reasonable. If you have to spend $$ to set this up, it is not and electronic single to 3 phase converters are more attractive. The case that I have seen were where someone got his hands on a surplus 3 phase motor for a fire sale price (probably ex-military stuff shipped to East Boondock and not worth the cost of shipping back out as often happens - the farmer lived in Moose Wallow which is somewhat north of East Boondock ).
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I agree- it is a fix dependent on what is available and cheap at that time and location.
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---------------- It's a point but --if you could start the first machine somehow (supply one phase and use a string on the shaft to spin it up or whatever) then the starting method might be actually easier for the smaller "load" machine - why bother with the first machine?
--------------------- If you have a 3 phase machine and a smaller single phase machine as well as some way to get the 3 phase machine starting to turn in one direction or the other, you can try it.
Cheers