Actually the power factor correction does not change at all with load.
Changing the load only changes the real power and the power factor
caps only change the imaginary current. The effects of power factor
are much more obvious at no load, so do power factor correction at no
load. If there is always going to be a good sized load, then power
factor correction is a waste of time.

If you measure the current to just a PF cap across the line, you will
know the imaginary current that goes thru that cap. ( slightly off for
puritans, but close onough for the real world ). Then measure the
current of the motor with no load and no PF cap. Then put the PF cap
across the input to the motor and measure the current. Now plot a
triangle with the side proportional to the three currents you just
measured.

Now rotate that triangle so the imaginary current is vertical ( the
current to just the power factor cap ). Now draw a line horizontal
from the angle of the triangle that is away from the imaginary current
line. And extend the imaginary current line down to the horizontal
line. The length of the horizontal line is the real current. And by
now it ought to be obvious to the most casual observer that it isn't
worth correcting the power factor completely.

Dan




(DoN. Nichols) wrote in message ...

Hmm ... you could start out by adding a respectable capacitance
(power factor correction) in parallel with the motor to reduce that
current quite a bit so you could then tune the converter, and then tune
the power factor correction capacitance for the optimum current draw.
Note that the optimum will shift somewhat depending on load applied, so
if you expect to have the idler running unloaded more than at a
respectable load, you probably should tune the power factor correction
capacitance for the no-load condition.

Apparently running these things unbalanced is a lot messier than
running them on the right no of phases.

I'm not sure about that as far as the power factor correction
bit is concerned. It is just that if you have the right number of
phases available, you also typically have beefier breakers and wiring
available to start with.

Also -- I *think* (but I don't know for sure) that a fully
loaded motor would have much less need for the power factor correction.

Good Luck,
DoN.