Re: Stepper Dissasembly

Hi,

A demagnetized motor is similar to a motor with a shorted turn. In
both cases the winding inductance drops to near zero ( less than 10uH
in my experience). A switching type drive, (chopper if you will)
depends on a reasonable V/L value, where V is the power supply
voltage and L is the motor inductance. Allowing for a 5uS blanking
and comparator response time, a 48V supply and 10uH inductance means
24A before the loop can respond. This is death on a MOSFET with a
rated max drain current of 15A.

The pulses will be short indeed but the drive will destroy itself
before anyone notices and corrects the problem, (1 to 5 minutes).

Mariss

--- In CAD_CAM_EDM_DRO@y..., stratton@m... wrote:
> Please elaborate on how damaged motors 'murder drives'?
> Do they generate excessive back EMF or something?
>
> My limited experience with small chopper drives is that they don't
> seem to care if you short the outputs... they just produce very
short
> chopping pulses.
>
> As for why it was in the trash, academics throw out lots of stuff,
> especially when their lab space is being renovated. So it is an
open
> question... I got a lot of goodies from that lab though.
>
> thanks,
>
> Chris