RE: (ET) ET power

[Larry Elie <lelie ford com>]

Getting long here....

Steve Naugler wrote;

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.

Ah, but there's the rub!  Why should the rating E15, E20 etc. include the 
accessories?  
An E12/E15/E20 all have the same 6 batteries.  They use the same 
accessories.  
The difference would have to be in the main traction motor.

;    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

<snip original>

Dean in turn replied...

;Hi.....   I'm here to confuse things even more yet....
;According to an old Popular Science article I have from June 1970, the E12
;is comparable to a 10 HP gas, the E15 is comparable to a 12 HP gas, and 
the
;E20 is comparable to a 14 HP gas.  Can anyone verify this?  I tend to
;believe it because the I think the heavy use attachments are the same no
;matter what large frame tractor they go on. Or did a blower or tiller for 
a
;E20 have a larger motor?  If they were the same, then the difference is in
;the .3 kw larger traction motor in the E20, which doesn't add up to 5 HP. 
;I think the E20 also had a higher amp hr battery back as standard
;equipment.
;Dean A. Stuckmann


Dean, I also have that article.  That is only PART of what it says.  It 
also says that 
the motor in an E12/E15/E20 can put out 30 (!?!) Hp, with the E20 being 
able to 
put it out longer.  It isn't true and casts doubt on the rest of the 
article in my eyes.  
They must be inferring duty cycle, but I suspect what they really mean is 
that the 
motor in a tractor can put out a similar amount of torque as a gasoline 
tractor that 
puts out 30 shaft Hp at high RPM.  


Then Paul wrote;



;For what it's worth, and as you'll see it isn't much, here are the specs 
on
;my golf cart motor:  The service manual specs say "Direct Drive 36 volt, 
DC
;Series Wound, 2.0 HP at 2800 RPM".  The motor nameplate further specifies
;2.0KW.  It also has a goofy spec of "Rating - 0.5Hr".  This has got to be 
a
;duty cycle statement, but it doesn't say how long you are supposed to rest
;it after full power for a half hour.  There may be a standard for this of
;which I am unaware.  If this don't help, I hope it don't hurt.

;Paul Heinzerling  


The rating 0.5Hr is indeed one of the ways of writing a duty cycle.  In 
reality, it 
is just saying "50% of some time", and you shouldn't imply that time is 
more 

than a few minutes.

Now, to totally confuse things, people DO rate an electric motor at 
roughly 3 X of a 
gasoline motor, but this is because of the STARTING TORQUE.  The same is 
true of 
a steam engine; they produce gobs of torque at zero RPM.  At rated RPM, 
all motors 
are the same.  BTW, most gasoline engines are also designed for as less 
than 100% 
duty cycle, industrial engines being an exception.  If that isn't enough, 
the ratings on 
lawn equipment is on the ENGINE not the TRACTOR.  Drop a good 20% or more 
for 
reality.  A John Deere 12 Hp is doing real well to get better than 9 Hp to 
the wheels.  
I think this is part of the confusion as well.  The real POWER of the 
motor is simply 
the rate of doing work; the torque times the RPM.  The real power consumed 
is the 
voltage times the current.  The real efficiency is the power output 
divided by the power 
consumed.  If the traction motor can continuously consume 100 Amps at 36 
volts, this 
is 3600 watts, and assuming 1000 (not the perfect 760) watts per Hp, this 
is only 3.6 Hp.  
Now, I have seen over 150 amps (but not for long periods) on my E12, which 
is over 5 Hp.  
Not bad, but it doesn't prove much.

Larry Elie
Ford Scientific Research