Re: (ET) newbie

["Steven Naugler" <snaugler earthlink net>]

Larry....  I'm here to confuse things even more....

    The E15 was supposed to be comparable to a 15 hp gas tractor, and the
E20 a 20 hp, and so on.  If we use the rule of thumb that 1 hp electric
equals 3 hp gas, an E15 would need 5 total hp (15/3) electric combined in
all motors.  The 5 hp electric in turn would be 3.8 kw.  Subtract 1.5 kw 
for
the traction motor and the remaining 2.3 kw is for large accessories, such
as the snow blower.
    2.3 kw electric is 3 hp electric, and with our 3 to 1 rule of thumb, 9
hp gas.  If you only need 9 hp gas to run a 42 inch snow blower, that's
pretty good, but actually pretty realistic.
    The 1.5 kw for the traction motor is about right, but that is a
continuously rated 1.5 kw.
    Now take the 3 hp electric golf cart motor, which is equivalent of 9 hp
gas.  First, 9 hp is a pretty small motor for any lawn tractor, let alone a
hydrostatic one.  That 3 hp electric is 2.3 kw electric.  Now if we assume 
a
2/3 duty cycle, we can get about 1.53 kw.  The golf cart motor might be OK
is used only for a traction motor AND my assumption that it is good for as
much as 1.5 kw continuous.  As I am unsure of its real duty cycle, I would
only recommend its use for light traction duty.  But if you add the load of
a mower deck or any other accessory, you have a probable overload 
situation.
That is why I'd separate traction duty loads from accessory loads by using
separate motors.
    The bigger strike against the golf cart motor is the fact that it is
series wound.  Speed control becomes more difficult with it combined with a
hydrostatic transmission.  With a gear shifting transmission, speed control
would be easier, but a wound field or permag would be best for good speed
control.
    Hope this inspires controversy.

Steve Naugler


----- Original Message -----
From: Larry Elie <lelie ford com>
To: <elec-trak cosmos5 phy tufts edu>
Sent: Monday, June 07, 1999 2:29 PM
Subject: RE: (ET) newbie


> Steve, I'm puzzled here....
>
> In your reply to Jeff, you mention...
>
> ;    4.  Except for light use the 3 hp golf cart motor will probably be
too
> ;light.  Light use would be mowing so long as the mower deck had its own
> ;motor set.  Even the GE E15 and E20, which had 1.5 kW and 1.8 kW 
> constant
> ;duty traction motors used separate motors for accessories.  If you 
> simply
> ;replaced the gas motor with an electric you'd have to size it for
> ;simultaneously powering the traction and accessory loads.
>
>
> I agree with your whole post, but 760 Watts mechanical is 1 HP, and with 
> a
normal
> conversion efficiency, a good electric motor will do 1 Mechanical HP on
1000 Watts or
> 1 kW.  I do not know the designed duty cycle for the GE, but might 1.5 &
1.8 kW be
> a bit wimpy?  Or was it supposed to be 15 and 18 kW?
>
> BTW, for a good belt-controlled gear transmission, the efficiency is 90 
> to
95%, for a
> hydrostatic it is 65 to 75%, the losses are to heat.  A hydrodynamic
(car-type) automatic
> is about 80 to 85%, and a few were used on large Case farm tractors in 
> the
1950's.  The
> efficiency penalty is why you never see a hydrostatic on anything but
garden tractors or
> bulldozers, where the speed control ability outweighs the efficiency
penalty because you
> can get your job done quicker.
>
> Larry Elie
>
>
>
>
>