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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: Jonathan szarzynski at earthlink.net
Date: Wed May 24 16:31:53 CDT 2006

This brings up an assumption I made that might be wrong:

> Jonathan, I'd be careful about these bridges actually delivering
> 25A. Pololu made one with the VNH3SP30 and most only get 7 to 9A
> out of it. We know the chip on the board because we have also
> tried it. The most we've been able to get continuous with a fan
> is about 15A. It was rated by ST at 30A but I don't know how
> they made that claim. Also it was rated up to 36V operating with
> 10KHz. Parallax might have a later version of the chip, a
> VNH3ASP30, which we haven't gotten yet. It has a lower high
> voltage, limit 16V, and a higher PWM rate 20KHz. So. maybe, its
> problems are fixed. But I would be very skeptical. (We're
> checking on availability of the newer part again. Nope, no one
> has them yet we can find.)
> Now, if it is indeed 16V and 25A as they claim, you have 400W
> which is your half horse power. But I doubt you can get but
> about 2/3 of that continuously. You'll have trouble (as you are
> finding out) matching a 1/2 horse motor to that 16V upper limit.
> You know, a human can barely reach 1/2 horse power output for a
> brief moment. I think generally moving around (briskly), we only
> use something like 1/7 horse power. I think you are over
> designing for power anyway.
> Randy
> www.newmicro.com

My first concern is blowing out the speed controller.  I assume that if I 
hook up a 350W motor to the HB25, I wont burn it out.  I might not get 350W 
of power, but I wont burn out the controller.  Am I correct?  Or am I 
risking burning out the controller by trying to get 350W through it?

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