(ET) Re: new electrics

["The Nauglers" <snaugler earthlink net>]

With all this talk about new ETs and better or cheaper ways to make them
please remember that due to the limited energy storage on board our 
tractors
efficiency must be paramount.

V belt drives tend to be only 90-95% efficient when everything is in good
condition and clean.

Friction drives are 80-90% efficient.

Chains, again in good condition, are 98 % efficient, but high maintenance 
to
keep them in good shape in a tractor application.  Notice that they are not
used except in high torque attachments like the snowblower.  A worn, dry,
and/or rusty chain can have efficiencies as low as 60-70%.  The wasted
energy turns to heat and destruction of what is left of the chain and
sprockets.

Direct drive, like the mower decks, are 100% efficient.

GE used VX series V belts for the traction motor because the VX series V
belts are more efficient than the old A/B/C/D series V belts.  If the new
Poly V belts, which are like the serpentine belts on modern cars, had been
available when the Elec Traks were designed they would have been used
preferentially over VX belts.

What GE did was make a whole series of design choices to keep efficiency
high.  Where they lost efficiency was in the motor controls, and that was
mainly a limitation of affordable DC drive technology of that time.  If you
were, in your new tractor, to use a friction drive for the traction motor
and belts in the mower deck, and then allowed for lack of maintenance, 
you'd
find extra losses of 10-25% after 1 or 2 years of service.  I mean 10-25%
higher losses than in a tractor with direct drive to the blades, and a high
efficiency belt somewhere in the traction drive.

With respect to protecting the mower motor with a circuit breaker:  This
will not work well with a permanent magnet motor.  In permanent magnet
motors there is some critical armature current above which you will
demagnetize the magnets.  The friction washers, while crude, act as a 
torque
limiting clutch.  By limiting torque, you effectively cap the armature
current.  If you use a circuit breaker alone the current can, and most
likely will, pass well above that critical current before the breaker 
trips.

Steve Naugler
snaugler earthlink net