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

["Briggs, Michael" <Michael Briggs unh edu>]

Larry,

Ahhh, so presumably that is why so many people have fixed a similar issue 
with completely different things - because the different versions of the 
Elec-Trak control the progression through the speeds differently. On the 
E-15, is there any step in the progression that is intentionally dependent 
on the voltage across the motor (or measured somewhere else)? 
    My understanding is that time delay circuits are the only thing 
keeping contactors 1A and 2A from being given voltage to trigger (and 
short across one of the big toaster oven resistors). From the schematics 
in the service manual, it looks like terminal #11 is the ground side for 
contactor 1A (which seems to be permanently tied), and either terminal #4 
or terminal #10 is the one that provides 36 V to the contactor to cause it 
to short across R1. I'm having trouble figuring out how card 1 controls 
that though. Does moving the speed selector switch from first speed into 
second speed result in 36 V going to terminal #10, and there is a time 
delay circuit that delays that 36 V to getting to terminal #4 (and thus 
triggering contactor 1A)? Looking at the wiring diagram (figure 4-2) it is 
really hard to figure out what's going on between terminals #4 and #10, 
especially since there are no ground or 36 V labels anywhere, or any 
indication of which terminals are inputs from switches and which are 
outputs. 

    I've had issues with the time delay circuit in the past - primarily 
with the time delay that's supposed to keep you from going instantly from 
reverse to forward (so the time delay for reversing the direction of field 
current), resulting in a big EMF welding the reversing relay shut. 

Thanks,
Mike

________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________

________________________________________
From: Larry Chace <RLC1 etnainstruments com>
Sent: Monday, May 22, 2017 9:16 AM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) E-15 not getting out of first speed

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

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