Quote Originally Posted by John S View Post
Lee the accepted figure is 2/3 for a parallel wired motor and 1/3 for a series wired motor.
These are figures that Marriss Fremanis at gecko drive came up with and are repeated as law.

So a 3a motor in parallel take 2a and 1a in series.

However I have had clamp ammeters fitted to power supply leads and running a system under rapids and loads i have never seen these figures, they have always been far less.

In fact in many cases the figures have been very small, far smaller than I would have imagined so the 50% is a far more acceptable figure.

One machine I used to convert I used 650 VA transformers at 50 volt AC, in a cost cutting exercise, due to rising copper costs, I dropped to 500 VA and saw no difference, a drop to 400VA still didn't make a difference but going to 330 VA did,

So the drop from 650 VA to 400 VA halved the transformer cost.
Shouldn't be taken into account the motor amps/torque vs. the machine weight/working material?

If I put 3A motors on a belt driven PCB milling machine it is impossible to use that power assuming to have idle-current reduction.

I think the 60% rule for the power supply works only with toroidal transformers which have an instantaneous power at least 25% higher than the nominal, and with one PSU for all motors because it is unlikely to have all axis under high loads at the same time.

John, what rated current had the motors and drives for your conversion where you used reliably a 400VA transformer?