Re: (ET) E-15 not getting out of first speed

[Larry Chace <RLC1 etnainstruments com>]

Hi, again, Mike.  The various models of tractor use various means to 
control the acceleration.  Your E15 uses time delays to control the 
speed advance from electric speed #1 to #2 to #3 to Field Weakening; 
each delay is about 2 seconds.

The E12 uses a centrifugal switch to make sure the motor is turning 
fast enough before switching from speed #2 to speed #3 (the higher 
speed for an E12).  Other permanent magnet motored tractors also use 
this technique.

Early E20s use some transistors and diodes to check the motor voltage 
before allowing Field Weakening, thereby disabling electric speeds 6, 
7, and 8 if the motor is working hard.

Later E20s (and my I-5) use a relay to sense the motor voltage and 
thereby control the use of electric speeds 3 through 7.

So, for your situation, the other tractor models aren't relevant even 
if they have exhibited similar problems.  (Though it is really 
difficult to imagine *what* could be causing the problems you've 
seen...)

GE was experimenting, you might say!  Also, the foot pedal controlled 
E20 and I-5 perhaps didn't need as much automatic control as did the 
hand operated speed controls.  I use both types of controls and each 
has its own advantage.

I've found it useful to have an extra toggle switch that disables the 
higher field weakening speeds.  On the E15, that switch permits the 
electric speeds 5, 6, and 7, so when I push the hand throttle full 
forward, I get electric speed 4 (one stage of field weakening); 
that's just a small increase over speed 3.  On the I-5, the switch 
permits the use of speeds 4, 5, 6, and 7 (all of the field weakening 
speeds).  That lets me just floor the pedal while remaining in speed 
3; that is similar to the "cruise control" but isn't locked in, so I 
can lift my foot to slow down or stop.  Another small modification 
provides for dynamic braking by keeping the field energized (from the 
shorted armature acting as a generator!) until the tractor stops 
(which happens rather suddenly!).

Too much blathering -- sorry!

Larry Chace, Ithaca, NY  I-5 and E15