In article ,
robgraham writes:
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 ?

I think most electric mowers are universal motors (i.e. with
brushes and a commutator). Certainly they were 8 years ago
when I last bought one -- I had to go some way off the beaten
track to find an induction motor mower. I've bought two over
the years -- I think they're both German but different makes
(both still working fine, although I've had to replace the
run capacitor in the 15 year old one).

The torque profile of a universal and induction motor is quite
different. An induction motor doesn't have much starting torque,
but when it's nearly up to speed, there's quite a lot of torque
to maintain speed, which makes it good for a mower. A universal
motor has a high starting torque, but low torque when up to
speed, which means it easily slows when under load. That isn't
good for a lawn mower. Universal motors also spin too fast for
direct coupling to a mower blade. You will also find you need
around 30-50% more powerful universal motor mower to get the
same cutting power as an induction motor. Universal motors
seem to get much hotter, but that may just reflect cheap lower
quality motors rather than any inherent reason.

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

How many AHrs is the 36v Li-polymer battery?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]