Re: (ET) Traction motor current

["Paul A. Cianciolo" <paulc snet net>]

Hello Folks,

It is really good to see all this activity here on the electrak reflector
Larry I was very interested in all your comment.

I think 1 reason that my E20 did so well is the weight  distribution.  4 of
those 6 batteries are sitting right over the rear wheels.
Although others havce the benefit of running 70 lbs more wheel weight than 
I
had and bigger heavier rear ends.

This is the component that I fear might fail if I were to build and enter a
machine in the   superstock class which allows big tires and
lots of additional weight.

Another problem I see with the gas tractors is the application of thier
power to the ground.  Most have clutches or belts and a few are
hydro's.  Like Larry says some of the hydros never make it to the point
where they lose traction,  the go into an over pressure condition and the
tranny slips.  The clutch and belt drivers need to slip the the power to 
the
rear wheels gradually.  I have seen this result in
heating the clutch and it slips or letting out too quickly and engine RPM
drops off too fast and the engine stalls.
The other thing I see happen a lot is a guy will just snap the clutch out 
so
fast that the rear wheels will just spin.

The E20 seems to apply the power to the ground in an even ascending 
fashion,
even if I slam the pedal to the floor.

I have come across a couple of high current shunts.  A 150 amp a 300 amp a
400 amp and a 1000 amp
I will insert the appropriate version in line with the battery pack and see
what peak current is when I get some time.
I will also try to see what the colors on the meter correspond to what pack
current .

Just my comments

Paulc
W1VLF
Cloudbounce Webpage  http://www.qsl.net/w1vlf/

1986 Vanagon Gas
1982 Vanagon Diesel  Turbo Diesel 1.9
GE Electrak E20 and E15  electric tractors
First place in local tractor pulls  at 1750 LBS
With Stock E-20 Electric tractor
----- Original Message -----
From: Larry Elie <lelie ford com>
To: <elec-trak cosmos5 phy tufts edu>; 'Rhett T. George' <rtg ee duke edu>
Sent: Tuesday, October 26, 1999 1:00 PM
Subject: RE: (ET) Traction motor current


> It doesn't shock me.  But I don't have the whole answer.
>
> Gas engines are a bit wimpy.  A "20 HP" gas garden tractor is really 20 
> HP
> under ideal conditions on a test stand, at one specific RPM, at one
temperature,
> one altitude or barometric pressure.  Real life is often 75-80% of that 
> at
full throttle;
> partly because full throttle is just that-- it doesn't at all imply max
HP.  For example;
> full throttle standing still just puts the engine at max RPM-- for a 20 
> HP
garden tractor,
> full throttle standing still is probably 1 HP, if that.
>
> Slug a gas engine by asking for too much torque, and the RPM drops off.
For a
> 3600 RPM/20 HP engine at 1800 RPM and you do NOT get 10 HP; the torque
> curve isn't that flat.  You might get 5 HP.  Slow an electric motor and
the
> torque does just fine.  That's why a GE pulls so good.  Only a steam
tractor
> would beat it (steam puts out max torque at 0 RPM).  Diesels do a bit
better than
> gas for low end torque, but not in the class of steam or electric.  BTW,
for low torque, high
> RPM use, a gas engine is quite good.  That's why we have gas cars,
motorcycles, etc.
>
> Then there is drivetrain loss.  Many garden tractors are hydrostatic, the
output of the
> shafts is 75% of the input power, the rest lost to heat.  Belt drives are
95%, and a
> belt often drives either the transmission or the hydraulic pump.  GE's
also use a
> belt(s) so that part is even.
>
> I did a test of circuit breakers for an unrelated FEA some 20 years ago
for my
> previous employer.  I'm sure you can look it up, but most trip in
milli-seconds
> at TWICE their rating, and after tens of seconds at 15-20% above their
rating.
> At say, 5% over their rating, they trip after HOURS, depending on the
ambient.
>
> Now, let's talk about that tractor pull.  Say the E20 put out 65 amps for
10 seconds at
> an honest 36 volts (My tractor is usually 38 V except right after charge
when I get 39V+).
> I get a tad over 3 HP.  But that isn't what happens in a tractor pull.  I
could use a 1/2 HP
> electric winch and pull SEVERAL tons at a low speed.  All that is 
> required
is pull.  You
> get that from two things; traction (and GE's are heavy!)  and torque.  I
have a 20 HP gas
> Oliver Cleat-track (a bulldozer) that weighs 10,000 lbs and (at 1 mph...)
can pull my dad's
> Massey Harris 44 (a 50 HP gas tractor weighing 8,000 lbs with duels)
backwards
> quite handily.  It can't work a field as well because the work depends on
the HP.
> Traction and gearing are important.  Assume the competing 20 HP gas
> tractor is a hydrostatic.  The engine is running at a high RPM, but NOT
the max because
> the designer matched the pump load well to the engine.  The engine may be
putting out
> 15 HP.  The Hydro drops it 11.25 at the axle.  If everything I said was
true, it should win
> a pull with an E20.  Neither is pulling the load far, so something like
inertia may make a
> difference.  I don't think HP is the best measure of what goes on.  All I
can think is that
> the hydrostatic has waste-gates (spring-loaded poppets) on the pressure
lines to prevent
> it from an overload from damaging the pump, and it really couldn't put
more than a few HP
> to the wheels.  That's conjecture.  I really don't know why an E20 can
beat a 20HP gas.
>
> Any better ideas?
>
> Larry Elie
>
>
> ----------
> From: Rhett T. George[SMTP:rtg ee duke edu]
> Sent: Tuesday, October 26, 1999 11:13 AM
> To: elec-trak cosmos5 phy tufts edu
> Subject: (ET) Traction motor current
>
>  - GreETings -
>
> Occasionally someone raises the question of maximum traction motor
> current.  Circuit breaker CB 1 is in the armature circuit.  If these
> are marked as circuit breaker are usually marked, that is, the current
> rating is stamped on the end of the reset button, then the E 20 has
> a 50 A breaker and the E 15 a 40 A breaker.  Now 50 A times 36 V yields
> 1800 W or 2.4 HP.
>
> Does this seem reasonable in terms of the performance of the E 20 or
> other tractors in the line-up?
>
> Rhett George
>
>