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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: michael at michaelshiloh.com michael at michaelshiloh.com
Date: Tue May 23 17:15:41 CDT 2006

On Tue, 23 May 2006, Randy M. Dumse wrote:

>>  The big question I have is whether 2x a parallax HB 25 motor
> controller
>> driving a 350W scooter motor will get the job done,
>> ...
>> I want to use Parallax’s new HB-25(amp) motor controllers.
>> (http://www.parallax.com/detail.asp?product_id=29144) It can
> control a motor
>> up to ½ Hp.  They are relatively inexpensive and I like
> parallax’s products,
>> but I am having a hard time finding motor/gearbox combos that
> are close to ½
>> Hp.  Any suggestions here would be fantastic.
> 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.

My experience has been that those claims are made assuming you keep the
junction temperature at or below spec, which is almost always impossible, so
you always have to derate them by quite a bit.

Since everyone automatically assumes this, and derates across the board,
companies that want to be honest nonetheless have to quote current rating the
same way, or else suffer in comparison.

I'd love to hear some expert opinion on this.

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