Re: Power Supply for 4-axis CNC stepper driver

Dave,

The difference between the calculated power using motor current and
resistance ratings and using the 66.6% of phase current times supply
voltage relates to the "rarely extract full mechanical power" part of
my response. The motor current times resistance will specify the
power consumed by the motor's resistive losses while at rest. If the
motor is being driven by a chopper type drive there will be
additional losses due to magnetic hystersis, not a lot, but still
present. The major difference comes from the mechanical output of the
motor. Most systems never come close to extracting full mechanical
power from the motor, nor should they be expected to do so. Typically
only systems like fans or pumps succeed in extracting anything near a
motors rated mechanical power. BUT, it you did extract full
mechanical power from the motor, you would find that it would be
drawing the rated phase currents at near the power supply voltage,
not at the voltage implied by resistance times current. This would be
due to the back EMF and the inductance effects of the motor windings.
Remember that power is RPM times torque, so a stepper motor at rest
is producting no mechanical power. To get full mechanical power you
must be spinning the motor fast and loading it at high torque,
something our CNC motion systems don't typically do. Hence my
comments that the 66.6% of phase current assumption is very
conservative. Many systems will operate quite well if you used 25% of
phase current for your calculations.

Regards,
Steve Stallings
www.PMDX.com


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@y...> wrote:
<snip>

>
> Interesting. If the motors are 2.4 volts and 6 amps or 14.4 watts
> times 4 motors for 57.60 watts total, why is the secondary selected
> for 1,032 watts ? (43 volts times 6 amps time 4 motors ?) why not
> the 60 VDC final voltage times 6 amps times 4 motors ? (1,440

watts?)

>
> IIRC, this question was asked some many months ago, but was never
> answered. Maybe one of our guru's can give the definitive answer ?
>
> I'll put it in the files section for posterity.
>
> The 1.8 times rating for the RMS in the DC filter is fine, but the
> above ratings are worlds apart.
>
> On another note, I had thought Mariss offered ratings (5x to 25x)

for

> his drives, not all drives. I have seen a few others, like the
> AutomatonDirect line that have 2.4 volts motors but one of the

drivers

> are 150 volts DC.
>
> I know that Mariss's numbers work pretty safely, universally, but I
> had thought other manufacturers have other ratings ??
>
> Dave
>
>
>
>