RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver

> 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.
>
>
> 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.

Back EMF. (EMF = electromagnetic force)

You can amuse yourself by hooking up a relay so the power to the coil runs
through the contacts; the coil powers up, relay closes, coil loses power,
relay opens, and repeat. As this happens you generate large sparks across
the connections of the coil. Don't hold it in your hand.

You also create a lot of radio interference (static), less of a problem
these days as no-one listens to radio and TV has gone digital. Your stereo
might pick it up.

That big spark is what happens when you unplug the stepper while powered up,
and that's what kills the driver.

Tony