On 01/06/18 00:04, Andrew Gabriel wrote:
A universal motor used in most electric mowers is exactly the
opposite way around - lots of starting torque, but it can't
maintain speed when cutting, since a universal motor has to be
slowed much more under load to generate torque. Also a universal
motor spins way too fast, so it needs additional pulleys and belts
to run the blade at the right speed for mowing. This is a lot more
to fail - motor brushes, and the belt drive have limited life.
Generally, the build quality is way lower than induction motor
mowers and the efficiency lower, so needs a higher power rating
for same width cut (and motor runs much hotter, which also doesn't
help the longevity).

This is all utter codswallop.

A properly designed and near 'perfect' motor will genee maximum torque
one RPM below 'free runnimng'

The theory is simple. The motor will spin till the back EMF - a product
of the speed, number of turns on the armature and magentic field -
matches the applied EMF.

When a load is applied if the motor drops speed, the current will
incerase until the speed is retired, less any copper losses.

That is the EMF and RPM always matches the applied voltage minus IR
losses in the copper..

On good motor this can result in near instant burnout when stalled.

What I suspect you have encountered is 'stall proof' motors that
deliberetely have far top much resistance in the windings.

Induction motors are crap really for serious power. Obnce they lose
synchronism, they are useless.


--
€œA leader is best When people barely know he exists. Of a good leader,
who talks little,When his work is done, his aim fulfilled,They will say,
€œWe did this ourselves.€�

ۥ Lao Tzu, Tao Te Ching