Re: [CAD_CAM_EDM_DRO] stepper driver-transformer sizing question

On Wednesday 31 December 2003 06:36, Scott Riddle wrote:

> I am a little confused on sizing a transformer to drive some small 30-
> Oz-in bi-polar steppers. They are rated at 3 amps/phase 2.1Vdc and
> the IMS IB462 drivers I have are good for 12-40V 0-2Amps 160Watts.

yes ..and no. You would never see 160 watts, because to deliver the 40V at 2A
the motor would have to be spinning, and that would imply that both phases
are not on continually ...

> What I am thinking is that the motors can take 6 amps (3 per phase).
> But can the motors only take 12.6 watts (6A x 2.1Vdc).

nope. the 2.1Vdc is the DC voltage drop, whilst in motion the signal is AC
and you will see more than 2.1V across the windings ..

>I would like
> to just buy 1 transformer to supply power to 2 or 3 steppers.

Size the transformer at 2/3rd of the motor plate rating .. in this case your
stepper drives are not up to delivering the full current the motor can draw,
so size the power supply for that, 2/3 * 2A * 3 motors = 4A. If you want to
build a supply that will be able to drive the motors to their full potential
if you got hold of some 3A stepper drives, then build a 6A supply ..

> I am
> not looking for high speed mainly low speed high torque.

are you SURE about that? .. if you are not driving your motors to AT LEAST
corner speed, and preferably above, you are not getting anything like the
amount of power out of them that you can ... if your application needs lots
of thrust at low speeds, gear the steppers motors down a LOT .. contrary to
what some people believe, stepper motors need to spin to perform, if they are
not spinning to at least corner speed, you have got your gearing wrong, and
you will be getting less thrust out of them than you could, plus bigger steps
and worse acceleration. For high torque output you need to gear the motor
down a lot!!

If you have geared the motors to always run below corner speed (ie slowly)
then you could reduce the size of the supply too, as you will never be able
to operate the motors in the region where they can use the current available.

> Would I also need to run
> resistors on series with each driver to limit the current each driver
> would be able to recieve?

No, thats the job of the stepper driver ... that will handle the current
control.

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