On Tue, 4 Apr 1995, Dave Kautz wrote:

>   Doesn't the resistance of a DC motor vary with rotational speed? I remember
>   something faintly about a counter-electro-motive-force i.e. the motor is
>   generating at the same time it's motating. 

Yes, that's what limits the motor's top speed.

> 
>   Here at work they always give things with motors a "locked rotor" test to 
>   make sure it doesn't catch fire if it's seized. I thought the extra heat was
>   due to the extra current being drawn on account of the device not turning.
> 
> 
>   I'd like to understand more about the operation of electric motors, so 
>   someone please correct me if I am mistaken.

Nope, you're completely correct.  With the motor not turning, the 
induced "counter" voltage it at it's lowest so the motor is passing
it's maximum current.

>   Thanks,
> 
>   Dave
> 
> 
> 

Cheers

<sstones@io.org>
SStones             Toronto,  Ontario.