Re: [CAD_CAM_EDM_DRO] Arc Welder Power Supply for steppers

Scott Riddle wrote:

>I searched and did not come up with any one else asking this question
>so here goes. I have been looking for a cheap power source to power 3
>Nema 23 steppers and I happened upon a DC arc welder for free. It
>puts out 52 volts open circuit and 25 at max load (180 amps). I of
>course never hope to hit 180A. But what I am wondering is if I dial
>it down to its lowest amp settup ~30 could this be a viable power
>source for my steppers?
>

Unless you want to turn the motors and drivers into puddles of glowing
metal,
NO WAY! Buzz-box welders are constant-current sources, not constant-
voltage. As the motors started, stopped or changed speed, the DC supply
voltage would be going up and down all over the place.

> Would I need to run some resistors in line
>with the welder to limit the current. I am thinking of adding a fuse
>to prevent any high amperages from burning out the driver board or
>motors. The steppers, I think, are around 6V so the ~52V from the
>welder should work well.
>
>

Just forget this, unless you need it as a welder. Connecting 180 Amp
supplies to a stepper driver that need 3 amps is just asking for trouble!
A small power supply that weighs under 15 Lbs should be fine, and you
can run it off a 120 V outlet.

>Another related question I have is on the rule of thumb I see often
>of supplying 20-25 times the rated voltage on the stepper motor. Does
>this always hold true and for all Volt steppers. The reason I ask is
>that I see some steppers rated for 12V. This would yeild 240+V power
>supply requirements. From what I understand this higher voltage is to
>get better responce from the steppers. At what point do you limit the
>voltage. One sure limiter is the driver boards voltage limit but are
>there others?
>
>

Stay away from 12 V stepper motors. These are used for floppy drives and
such, where there is no resistor used for current limiting. The winding
resistance is made high on purpose, to save the cost of a resistor. These
steppers are good for about 50 steps/second, maximum. that's fine for
a floppy drive with 40 or 80 tracks, but is a bad choice for a machine
tool. You need motors with much lower resistance and inductance to
get decent motion speed.

Jon