The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator
to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or two) at
a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some motors
might have three poles but that only 1 configuration , is a five pole
motor 5 phase? and a 7 pole 7 phase? and you cant feed a permanent
magnet motor AC current so to call a dc motor ac is simplifiing things
to far


--
Kevin R
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