Re: (ET) Re: new electrics

[Dave & Debbie Barden <daveb seanet com>]

and what about Polychain made by Gates.  Goodyear has a similar toothed 
belt 
also but it's teeth are aligned in two rows forming  chevrons that has the 
added advantage of being able to stay on the pulley without shoulders.  
that's 
a pretty crude description but I wonder how these belts compare efficiency 
wise 
and what the downside is to them?

dave
seattle

> 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
> 
> 
> 
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