Re: [CAD_CAM_EDM_DRO] Power supplies sizing

wanliker@... wrote:

> If I am using three motors rated at 5 amps, in the X.Y, and Z axis. Do I
> have to have a power supply rated at a full 15 amps, or can it be a
> percentage of that? I assume that most of the time, all three will not be
> running at full load, am I correct on this?
> Small home machine, not commercial duty.

Is this steppers or servos? The answer is different.

A chopper-type stepper drive will allow motor current that is much higher
than power supply draw, when the motor is stationary. For instance, if
the motor is rated at 3 V 5 A, and the DC power supply is 60 V (20 x motor
voltage) then the current will be (very roughly) 1/20 of motor current,
or .25 A. This relationship does not hold when the motor is moving, and
it depends on how the energy in the windings is removed. If it is dissipated,
as most do, then the power supply draw may peak at twice the rated motor
current (as there are 2 windings each at the rated current). So, the worst
case could actually be 30 A! but, that would be a very unusual case, with
all 3 motors running at high speed and high load at the same time.
When motors are slowing, they can actually put energy back into the power
supply.

With servo motors, the peak power supply current can equal the peak motor
current, only when the motor is running at high speed and high load.
very high torques can be provided at low speeds without drawing much
power supply current (as total power is small).

Note that most power supplies can deliver much more than their rated
load current for short bursts without harm. It is not necessary to provide
a power supply with a 15 A continuous-duty rating in an application that
will only draw this current for a few milliseconds an hour.

Jon