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(ET) Controls revisited

I haven't been keeping up, but I noticed a big discussion on ET controls a
ways back.  I didn't see anything about the version of E-12 I have.

It has a permanent magnet drive motor, no field coil.  The 4 armature
relays switch the motor current for forward / reverse, H-bridge style.
When the speed lever is "off" the armature is shorted, making a pretty
effective dynamic brake - I rarely use the foot brake.  This is opposite of
the tractors with field winding motors, that take off on steep hills when
you set the speed controller to stop!  It really messes me up when I use my
dad's tractor.  

Using a 1 milli ohm resistor (0.001 ohm, *big* watts), and a storage scope,
I measured the peak locked rotor amps of the drive motor at around 300 
Amps.

The tractor originally had 3 speeds forward and 2 reverse.  The 2 lower
speeds were done with the usual big resistors in the front.  In reverse,
they just didn't allow the full power relay to fire.  The plastic wheel
doesn't have the bumps for the micro switch.

I made a foot pedal speed control with a rotary switch and linkage, using
the original speed control for choosing forward and reverse only.  Since my
foot switch has all 3 contactors connected, I have full power in reverse.
It is so much better.  I have a little delay switching from forward to
reverse, because I wired it so that the pedal has to be released before the
power will re-engage when the reverse (old speed selector) is thrown from
forward to reverse.  I can get to switching it very quickly, and so far,
have yet to burn out a contactor.  I never tried to smoke the tires, but I
have removed grass when getting in too much of a hurry changing 
direction...

I had to move some sand between truckloads (the big tractor was broken, and
I didn't have the Dynahoe yet).  The Elec-Trak moved 32 yards of sand that
day, making room for the rest of the deliveries 320 yards in all.

A couple of pictures:

http://users.abac.com/dandatief/house/outside/septic/sandm2.jpg

http://users.abac.com/dandatief/house/outside/septic/sandm1.jpg

Dave

Dave  Tief.  N1WWY,  Addie Tief.  N1XQP
Tribble, Noodles, Cecil, Magic, Ruby and Cinnamon
Visit our web page at http://users.abac.com/dandatief
See the bunnies,  generators, and progress on the owner-builder house