Re: [CAD_CAM_EDM_DRO] Need help with servo power supply design

cnc_4_me wrote:

>I would like some advice on how to calculate the proper power supply
>size for a 3 motor servo system as specked below. I also have a post
>from Mariss who has tried to help me.
>
>

A couple of points. First, these so-called bulk power supplies can
handle momentary
overloads if they are not too frequent. The motors cannot handle peak
torque for more
than a couple of seconds a minute, at most. Unfortunately, there is no
continuous
torque (or current) spec on these motors. With a 20 A peak current
rating, the
continuous rating is likely to be no higher than 4 A. So, the 3-axis
system could never
handle more than 12 A continuously. Another thing is that the PWM motor
drives
are power-in approximates power out. When the motors are exerting power
at low
speeds, the required voltage will be low. For instance, a Gecko 320
drive with a 60 V
power supply, and delivering 2 V at 20 A, will draw 40 W, or only 1.5 A
from the power
supply at 60 V. (2 * 20 = 1.5 * 60) So, these motors could all be
delivering peak torque
at low speeds and STILL draw less than 5 A from the power supply. The
only time the
current in approaches the current out is when the motors are at near the
full RPM.

So, what this all boils down to is that you rarely need as big a power
supply as you think.
A power supply with a 10 A (average) rating will likely be more than
sufficient for a
milling machine.

A router may need more, as it will be running at the top end of the
speed range, with lots
of rapid accelerations.

Jon