toroidal secondary coils and va usage

[Gads]

hello i need help with toroid selection. my calculations based on my motor
selection 2.3v,5.5a works out to 46-57vdc and 11a for 3 motors and 14.7 for 4 motors that i may want to run in the future for 4th axis.
this works out to 440va for 3 motors and 588va for 4 motors, these are odd
specs and voltages from what i see on ebay. can i go with a 800va 50v+50v
and just use one secondary coil. also good or bad having higher amperage available and correct voltage or lower voltage and correct amperage.
I do intend to add the 4th axis once i get my mill setup and running with 3.
any suggestions would be appreciated.
thanks gads

[daedalus]

first thing is you dont necessarily need the full current of all 4 drives running simultaneously, as you are unlikely to be running all 4 at the same time, so you could derate your power supply a bit. As for current, generally having extra current capacity is not a problem, as long as you make sure that you have some kind of overcurrent protection so that should a motor stall and start drawing its peak stall current, the drive will shut down. Note you need this either way, as should one drive stall when the others are not running, it will have more then enough available current to cook. It should be a feature of your motor driver, but check its set to an appropriate value.

As for the secondary windings, if your using 40v windings to produce 20a i think you should have both windings in parallel, as iirc the power rating for both secondarys.

As for power supply current vs voltage:
Amperage * Kt = torque
voltage *Krpm = speed

so if you want to have the full torque of your motor with reduced top speed then use correct current and lower voltage.