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Re: (ET) corded mower motor
I knew there would be someone out there with the exact info!
>>> Rhett George <rtg ee duke edu> 5/13/2005 12:50:51 PM >>>
- Greetings -
Bob Murcek asked about permag motors in corded lawn mowers. Methinks
there
are two reasons for using the permag motor with its bridge rectifier.
First - apparently lower cost in that the magnets are cheaper to mold
and
magnetize than the cost of winding a field electromagnetic.
The
1989 Ford (Mazda) Probe I used a permag starter motor. This is
a
high torque application.
Second - in coasting, back EMF is generated. By shorting this out,
i.e.,
shorting the motor when the switch is open, a large torque in
the
direction of slowing the motor is developed. This is simpler
than
using a friction brake with some linkage to apply it when the
blade
should stop.
With regard to the induction motor, the torque vs speed curve is not
favor-
able when starting with the blade in tall grass. It does not have
overload
characteristics that yield performance most users want in a mower.
Hope this helps.
Rhett
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