Subject: Re: Stepper Motors from Alternators??

From: [email-masked] (Robert Nichols)
Date: Thu, 12 Sep 1996 23:42:39 GMT

In article <[email-masked]>,
Tim Shoppa <[email-masked]> wrote:
:In article <[email-masked]>,
:Kevin  AstirCS "1U"   KO0B <[email-masked]> wrote:
:>
:>On a related subject: Does anybody else use 12VDC applied to lathe's
:>induction motor as a brake?  Take  an induction motor, and turn the
:>shaft.  Now hook it up to a car battery, and turn it again. Impressed?
:>Don't be lazy when tightening the chuck, and leave the belts a little
:>loose!  If you use something other than a car battery,  you need to
:>clamp the voltage to a reasonable level, as the motor becomes a
:>generator , and will try to raise the voltage.  A car battery just
:>absorbs it , but a "wall wart" won't survive this.
:
:Is a car battery substantially better than just shorting the wires at
:high RPM?  I could certainly see how it would help a lot at low RPM.

With an AC induction motor you definitely need the battery.  The motor
won't have enough residual magnetic field to do much as a generator.
Hit it with DC at some substantial fraction of the locked-rotor
Amp. rating, though, and *WOW* does it stop fast -- even faster than if
you hit the "Reverse" switch, and you don't have to worry about the
motor actually reversing if you mis-time it.

-- 
Bob Nichols         [email-masked]
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