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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: Randy M. Dumse rmd at newmicros.com
Date: Wed May 24 23:40:35 CDT 2006

> Or am I risking burning out the controller
> by trying to get 350W through it?

Yes.

When power electronics let go, almost anything can happen. You
can even burn out your computer from your H-bridge melting and
shooting your Vmotor supply into your computer systems 5V,
unless you use special circuits to snub problems before they
happen.

Usually the H-bridge will try to protect itself. But as I say,
anything can happen. We make a special H-bridge specifically
isolated so this can't happen, which is a pretty good trick, and
so lots more expensive. But that's another story.

It mostly depends on how the chips protect themselves. The
VNH3SP30 does a pretty good job of defending itself, normally
just shutting off its outputs when it gets too hot. Not always.
We've lost a number in testing as well. Remember, a motor is
complex thing. It also acts as a generator, and can convert the
vehicle motion into a voltage opposite what the H-bridge is
trying to put out.

Take for instance that 16V limit. Let's say you use a 12V
battery. You run your vehicle up to full speed. Now slam the
H-bridge on full the other direction. Your H-bridge is applying
12V one direction, the motor is generating 12V the other
direction. Are you now over the 16V limit for the part? And
what's the current going to do in that situation? See the sorts
of problems you can get into?

You generally see trouble in situations like this, where you're
slamming the system full forward, then full back, repeatedly,
and so on.

Randy
www.newmicros.com



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