Re: ATM - Fractional HP Motors for Grinding machines

[lowther@att.net]

Adam Perkins wrote:
> 

 
> I have no idea how a "2 speed" AC motor achieves its
> lower speed, but assume this one to have a "high"
> speed of 825 rpm (developing 1/4 HP at this speed).
> 

Ac motors 'natural' speeds come from the number of poles.  The 'regular'
1725 is actually a 2 pole motor with an ideal speed of 1800.  Losses
account for the 1725 rating.  I just gave a washing machine motor to
someone for a lathe.  After examining the schematic, it looks like they
use the low speed winding to degrade motor perfomance to get a lower
speed.  I could see no place where the hi speed winding was ever
switched out of the circuit, just where the low was switched.  I
remember years ago at a training seession everyone was shocked to learn
that washers use more power on low than high.  These motors even had
completely seperate  low windings.  I guess it must be an effect of
being off the 'natural' speed.

-- 
Ken Lowther
Youngstown, Ohio
http://www.atmsite.org