Re:low cost stepper driver

I connected my first steppers, ran the machine for about a month, then had a catastrophic failure. I replaced the motor and gecko and it worked for 2 years after that.

my second machine had the motors connected for about a year

my rhetorical question is why would anyone attempt to disconnect a motor from a powered circuit ?

if the design was so bad that the machine cut the wires, the builder has a lot more to worry about than if the stepper was able to protect itself.

I would offer that in most cases it is the initial wiring that was wrong that lead to disaster. but, once the machine has been tested, things no longer have the same risk factor.

Dave

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "John Dammeyer" <johnd@...> wrote:
>
> Dave,
>
> The same thing that makes the spark plug ignite the gasoline in a car is
> what blows up the stepper drivers when you unplug the motor.
>
> A simple non-CD ignition with breaker points allows current to flow
> through the primary winding of the ignition coil creating a magnetic
> field. When the points open the current stops and the magnetic field
> collapses. That 12V potential across the coil now turns into almost 200V
> for a very short time. The secondary of the ignition coil steps that up
> from 200 to 20,000 or more. Capacitive Discharge ignitions first charge a
> capacitor up to about 400V and the resultant spike goes to well over
> 45,000V.
>
> You cannot guarantee that when you unplug a powered stepper motor that the
> connector or switch won't have the contacts bounce on/off for a few
> micro-seconds or even milli-seconds. During that time the stepper motor
> windings behave just like the ignition coil and the resultant high voltage
> spike will kill the drives.
>
> That's why mechanical relays have a reverse diode across their windings.
> Stepper motors have current going both ways and the drivers are internally
> (or externally) protected while they are connected.
>
> John Dammeyer
>
>
> > Subject: [CAD_CAM_EDM_DRO] Re:low cost stepper driver
> >
> >
> > I have a simple machine that is made of MDF. it is not
> > designed to cut metal, just wood and plastics and such.
> >
> > 3 amp motors are more than enough.
> >
> > the machine cost under $300 to build (motors were free)
> >
> > it does not call for $100 each drivers.
> >
> > an hour to make a simple circuit board that will run the
> > drivers properly is worth the tradeoff. not sure why there
> > is an issue of disconnecting motors with the power on.
> >
> > it would be nice to make another one less than $100 in
> > drivers and power supply and motors.
> >
> > $33 and axis is not impossible.
> >
> > Dave
> >
> >
>