Rotary Phase Converter Questions - CNC grade RPC really needed?

[cncmachine.ca]

Im looking to purchase a rotary phase converter for our cnc machine. I know you're supposed to get a CNC grade unit, but is this really necessary? Thinking of getting a regular RPC in favor of cost.

Can somebody please describe how a CNC grade phase converter is better than a regular one? What exactly does it mean to be 'balanced', and what would happen to your CNC machine if the RPC wasn't balanced perfectly?

Also does it help to get an oversized unit? Would being oversized compensate for the fact that it's not a precisely balance CNC grade unit?

[Geof]

"Balanced" means that the voltage between each of the three lines is the same. CNC machines 'like' to have balanced three phase. I am not sure whether they could run okay on an unbalanced supply but most of them have sensing circuits that will shut the machine down if one leg of the three phase drops too far below the others.

Is it not possible to get a three phase supply at your location?

[Al_The_Man]

RPC's generate a third phase from the product of the two 1 phase lines fed to the motor, the voltage is stabilized as best as possible using capacitors connected from the third phase to each of the 1ph lines, Generally the 3rd phase is higher initially to counteract the variation that is going to occur between the 1ph pair and the 3rd line when you put a load on them.
It depends on how well the tuning as to how close the voltage is going to remain on the 3rd phase with varying load span.
If the 3ph on the machine is for 3ph motors only, then there is not usually a problem, if you have control power on the machine that is fed from a single phase transformer in the enclosure, make sure that the 240v 1ph lines that are passed straight through from the RPC are feeding this 1ph transformer and not fed by the 3rd phase for stability purposes.
Al.