Re: [CAD_CAM_EDM_DRO] Re: servo voltage question

Mariss Freimanis wrote:

>Jon,
>
>Even if it is a "minor war" I never received the invitation to
>participate; I feel let down.
>
>

Oh, but you did participate! it was a while ago that the last salvo was
fired,
probably a year at least.

>Switching type drives apply a voltage to a motor. This voltage has
>little to do with the power supply voltage. All the motor sees is
>some percentage of that.
>
>Voltage by itself doesn't really matter and a user doesn't control it
>or measure it anyway. What matters is a motor's maximum rated RPM and
>torque.
>
>It is perfectly OK to use a 40VDC rated motor with a 70VDC power
>supply so long as you don't ask for any speed over what the motor is
>rated for at 40VDC. The motor won't know any better because all it
>will see is 40V. The PWM will go to a 60% duty cycle (0.6 times 70V =
>40V more or less). Everything is cool then.
>
>

OK, this is what I have been saying for some time. Maybe we had a
misunderstanding.
It was my recollection that you told customers and others that you
strongly advised
against using a DC supply voltage above the motor's rated voltage.
Perhaps what you
were trying to get across was to avoid putting voltages above the rating
across the motor
terminals.

>The drive is equipped with a current limit trimpot. Current is
>limited on a pulse-by-pulse method. If you have a 15A rated peak
>motor, set the limit on the trimpot to that then.
>
>Overvoltage under your control by not asking for a speed above what
>the motor is rated for. Over-torque can be prevented by setting the
>torque limit trimpot correctly. That's what it's there for.
>
>Otherwise go with your 72VDC supplies for 40VDC or even 24VDC motors.
>They won't know the difference if you behave.
>
>

Well, as I point out in another post, with the ubiquitous Ametek motors,
you MUST
get above rated voltage to even achieve the peak current rating of the
motor.

Jon