Hydrostatic is 65 to less than 80%, depending on many factors including
temperature. It's used on gas tractors for connivence, nothing
more. Hydrodynamic (car automatic) can go much higher, but isn't really
variable speed at all; just shift-on go.
It's always funny when our 30 year hindsight realizes that people 30 years
ago weren't dumb. If electric tractors rise again, it will be because
someone has a cheap battery or ultra-cap... or perhaps uses a cheap fuel
cell. This market is already poisoned, and no large marketing guy will
touch it. Once business people 'know' that no one will buy something,
they stop trying. Another example: Diesels have 50% market penetration
in Europe at higher fuel price. In the US it's 5%, because GM failed
marketing it in 1980, and now everyone 'knows' that no one will buy
them. Service is part of that. They tried, but not well. People paid a
large premium to buy the early ones, and then averaged over $1,000/year
for repairs. I'm afraid Honda or Toyota may poison the electric market
for the next 25 years too. If they start passing on real their costs,
they will indeed kill the market. I'm glad GM pulled out before they
poisoned the electric market. No one will take large los!
ses for long before they pass them on or pull out, and pulling out to
give others a chance is the BETTER choice for everyone else.
Larry Elie
-----Original Message-----
From: Ralph & Elaine Vogan [mailto:ralphgv centurytel net]
Sent: Friday, February 20, 2004 3:33 AM
To: Elec-Trak
Subject: Re: (ET) Re: new electrics
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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> Elec-trak cosmos phy tufts edu
> https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>
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