RE: (ET) Traction motor current

[Larry Elie <lelie ford com>]

Thanks for the info.  I did some thinking and 'clip-on' over the last day, 
and think I understand 
a little better than I did yesterday....

I guess I never really understood how a C.B. worked....  My hall-effect 
clip on measured over 
100 A with ease on the E12 (40 A breaker).  We have already have had 
people on this list that 
saw over 600 A for brief periods.  So I started to ask how breakers REALLY 
work.  The ET's 
breaker is rated at 220 V.  I thought; so what, current is current, right? 
 Wrong.  The breaker in 
an ET is a bimetallic strip.  It works by heating the strip to a given 
temperature.  Current?  Well, 
the TEMPERATURE is related to the POWER (current x voltage) and time.  
Guess what?  
At 36V, the power, and hence temperature, through that bimetallic in the 
breaker is about 1/7 of 
what it would be for 220V.  Hmm.  Me thinks my 40 A breaker will trip at 
240 A or thereabout 
continuous, and probably at 500 A or so after a few seconds.  Even for 
fuses, folks, the temperature 
is what does the break, and the temperature is related to the power.  
That's why it isn't a good 
idea to use 110V stick fuses in a 12V application.  I should have known 
better.

What does this mean?  Well, it means that an E20 may indeed put out over 
20 HP at the motor 
shaft for minutes.  My guess is it will put out 30 HP for a few seconds... 
 Interesting.

Larry Elie


----------
From:   Sarah Kanary[SMTP:myhomebu kanarysweb com]
Sent:   Tuesday, October 26, 1999 8:54 PM
To:     Rhett T. George; elec-trak cosmos5 phy tufts edu
Subject:        Re: (ET) Traction motor current

Rhett, a small clarification is in order as to which circuit breaker does
what. C.B. 1 is located on the traction motor, and provides primary overall
overcurrent protection for most of the vehicle's wiring.C.B.2, located on
the "firewall" under the hood, protects the tractor's wiring in the event 
of
a short circuit in one of the charger's diodes.C.B. 3, found only in the
E-20 and I-5, is located in the traction motor field case, provides 
overtemp
protection for the traction motor, in the event of prolonged "low level"
overloading that would not be large enough to trip C.B. 1, whose rating on
the E-20, and I-5, is 100A .This rating represents the absolute, long term
current draw that the power pack can be exposed to.Short circuit 
protection,
finally, is provided by the fuse link attached to the power disconnect.
            Why this lengthy explanation, you might ask? Because the
maximum, short term current draw, and therefore, torque output, of the
traction motor, will be considerably higher than your calculations would
suggest.Some have been skeptical of some of my observations in the past, 
but
if you want to play "Mr. Science", and experiment a little, you can make
some surprising discoveries. It takes C.B 1 time to "get hot", so until
then, the tractor hasn't figured out that you are trying to drag a one ton
dumptruck up hill in to your garage!Much, much more than 100A is demanded 
in
this situation. Have fun, be EV ing you!

RJ Kanary@ Bandi Bros. Inc. ATRA ® Member Shop
Member TRNi 1&2 Since 1998
ASE® Certified Master Auto Technician Since 1992
Member Tech Line Associates Since 1987
rj kanarysweb com




----- Original Message -----
From: Rhett T. George <rtg ee duke edu>
To: <elec-trak cosmos5 phy tufts edu>
Sent: Tuesday, October 26, 1999 11:13 AM
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