Re: (ET) Re: new electrics

["Ralph & Elaine Vogan" <ralphgv centurytel net>]

Does anyone know the efficiency of a hydrostatic drive?  Use a single speed
motor and the drive for forward, reverse, and speed changes.  I have an old
White ice tractor with a very small hydrostatic drive unit bolted to the
differential.  It has plenty of power.  Or a hydrolic pump & motor to drive
the blades?

Ralph V


> 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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