Re: max. Servo motor voltage ??

Jon,

I am glad I saw your post before I went ahead and spent > $50 for a
new transformer.

I wonder if you or someone else on this group could help me evaluate
the suitability of a transformer that I have on hand.

The transformer that I have outputs 30 volts. I don't have an exact
figure for amperage, but I am confident that it can supply enough
current for my application. I was planning to use it to power some
servos using Gecko 320 amps.

The motors that I will use are rated at 24 volts, 1000 rpm max.
Continuous torque is 50 oz-in, peak is 100 oz-in at 6 amps. No Kv
listed (would it be 24 V?), but the torque constant is 17.6 oz-in-
amps. Terminal resistance is 3.3 ohms. I know these motors seem
small, but they will be used on a Taig mill with 10 TPI lead screws.

I was going to scrap the idea of using this transformer and was about
to purchase one at a lower voltage. With my limited understanding of
what you wrote, I realized that perhaps my transformer would be
alright to use, after all.

Thanks,
Tom Murray

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> There is no simple formula. With a motor rating point, say 24 V at
3600
> RPM, you can then
> make some calculations. Also, if you are given the motor's Kv
(velocity
> constant) that is
> a rating point of Volts/1000 RPM. First, determine the fastest
rapid
> feed rate you want, and
> figure out what leadscrew RPM you need to get that. Second,
convert
> that to motor RPM
> depending on the belt reduction, if any, that is being used.
>
> Example:
>
> 120 IPM feedrate and a 5 TPI screw gives 120 * 5 = 600 RPM.
Assuming a
> 2:1 belt reduction, the
> motor would be turning 1200 RPM. With the above motor, it would
only
> need 24/3 = 8 V
> to get 1200 RPM at lo load. Now, if the motor had a peak current
rating
> of 10 Amps, and
> a terminal resistance of 2.5 Ohms (this is a hard thing to measure
> accurately on brush motors),
> you'd have 25 V of IR drop in the windings, so add that to the 8 V
and
> you get 33 V at the
> motor terminals. You need to add a bit more for drop in the servo
amp.
> Probably at least
> 10 V would be a good start. So, now, it looks like you need 43 V
> minimum to be sure you
> could get your full 120 IPM under load. The servo amp should see
to it
> that the motor
> never gets the full 43 V across it, especially at stall, so it
should
> not really exceed the
> manufacturer's ratings.
>
> Jon