(ET) corded mower motor

[Rhett George <rtg ee duke edu>]

 - 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