From: Kevin McMurtrie
Subject: Re: DC Injection Brake for Induction Motors???
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Tue, 01 Oct 2002 23:40:57 GMT
NNTP-Posting-Date: Tue, 01 Oct 2002 16:40:57 PDT
In article ,
Mike Poulton wrote:
>On 01 Oct 2002, John Woodgate said:
>> I read in sci.electronics.design that Tony Williams
>> wrote (in
>> <firstname.lastname@example.org. uk>) about 'DC Injection Brake for
>> Induction Motors???', on Tue, 1 Oct 2002:
>>>Note that (at every braking) all the kinetic energy
>>> is dissipated by the motor, presumably in the rotor.
>> ONLY if the stator is VERY firmly screwed to something massive. YOU
>> HAVE BEN WARNED!
>Presumably, you wouldn't be generating much more torque than the motor
>would normally produce, just in the opposite direction. Right? --
>Not only do I speak for my company, I AM my company!
>Live free or die!
It depends on external current limiting. The voltage cycling of AC
limits how strong the magnetic field will become and how much current
will flow. DC is limited only by coil resistance. A big AC motor may
have a winding resistance of under 1 ohm. Apply 120-something volts DC
to that and it stops _very_ quickly.
I tried it with a box fan motor once and it locked up hard. It surely
would have broken something if the blades had been attached.