RE: [CAD_CAM_EDM_DRO] Re: Power Supply for 4-axis CNC stepper driver

Hi Dave,

Eventually the transformer will smoke. Before my large transformer arrived
I was playing around with a 24V 1A DC supply; note 24VA. Two Size 23 1A
steppers. With both running the voltage would drop to 18V and the box got
really warm. Just think if I tried to use that 24VA supply for a couple of
Size 34 motors and a driver that tried to supply 6A per phase. Magic smoke
time.

Now failure on stepper conversions can happen for a lot of reasons. If you
full step, both coils are on so you need 100% of the motor nameplate current
to provide full torque. Remember Amps x Turns is what creates the torque.
Go and have a coffee and come back and the motors will be hot.
Micro-steppers never apply full current to both windings _at_the_same_time_.
The most you get is 70% at the same time. In fact because the windings are
rated to dissipate heat you could get away with running higher current
through the windings if you micro-step.

BTW, the only way to measure current on stepper systems is with a scope.
Don't bother using a DVM.

John Dammeyer

>
> Ah... I don't think I ever run near maximum so I cannot say I get full
> torque. I get movement and can run the machine(s)
>
> I don't know if the transformer would smoke or the voltage would drop
> off. Guess I have some testing to do so see if I'm not getting as
> much as I could.
>
> It is interesting that IIRC, the old rule of thumb was 66% of total
> nameplate for current ratings, but we are no talking double that,
> well, 1.8 times that anyway.
>
> Maybe that is why so many people have failed on stepper conversions on
> Mills ?
>
> Dave
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