Re: [CAD_CAM_EDM_DRO] current limiting power supply for stepper?

At 04:07 26/02/2003 +0000, you wrote:

>Is there any reason not to use a current limiting power supply with a
>stepper, so that higher than rated voltages can be used? (Of course
>the stepping sequence must use the same number of coils for each step).

No reason at all (other than heat dissipation - see below) - in fact that
is a technique used by these guys:

http://www.oatleyelectronics.com/kits/k142.html

who sell a stepper driver kit and a constant current source. The downside
is that the trannies in the constant current source will get VERY hot, as
they are required to dissipate a significant amount of power if the PSU
voltage is much higher than the motor voltage. The constant current source
must dissipate a similar amount of power as would a series resistor chosen
to reduce the motor current to its rated value.

Their website unfortunately doesn't make any statements about how much
current the stepper driver & current source can handle, other than it can
drive at least 2.66A - I guess part of the answer will be it depends on how
big the heatsinks/fan are. I emailed them a couple of weeks ago to ask, but
no response.

Because of the heat dissipation problem, most drivers these days tend to
use "chopper" techniques to control motor current, rather than linear
techniques.


Regards,
Tony