Re: (ET) how does the late model I5 speed control work?

[Chad Bush <bushman165s aol com>]

Charlie,

If you haven't received a response on this yet, here are a few ideas:

When the pedal is pressed all the way down from a dead stop, it still 
takes time for the armature to "spin up" and equalize the voltage 
across it. I say "equalize" freely, because what actually happens is 
that a large surge of current is drawn from the pack (bringing the 
whole pack voltage down) to get the armature to rotate with enough 
inertia to resist the field voltage. This large surge and voltage drop 
affects every component, and so as the voltage comes up from the 
initial surge, each speed will kick in up to the current position of 
the pedal. Make sense?

Now, when going up a hill, essentially the same things happen, just for 
a different reason. If the pack is weak or some connections are loose, 
you won't get enough voltage/current to enable that final armature 
speed. What the Power Pulse button does is that it actually shorts the 
first field resistor momentarily, giving the armature a chance to surge 
a little faster and allow a voltage spike across the armature 
(hopefully to a solid 36V). Once it reaches that speed and the power 
pulse button is released, it should be at the final armature speed 
without field weakening.

If you're consistently NOT getting that final speed, I would check that 
2AH relay and the 2A coil for loose connections or burnt contacts.

Someone please correct me if my theories are wrong. Hope this helps.

Chad Bush


-----Original Message-----
From: Charlie <medievalist gmail com>
To: Elec-Trak <elec-trak cosmos phy tufts edu>
Sent: Tue, Sep 4, 2012 2:53 pm
Subject: (ET) how does the late model I5 speed control work?


On my 1973 I-5, I have a "gas pedal" that contains some switches that
drop resistances out of the circuit of the traction motor armature,
and more switches that add resistances in series with the traction
motor field.

Normally, each switch is opened (or closed) in sequence as the driver
increases pressure on the pedal, and as each armature (toaster)
resistor is dropped out, or field resistor added in, the tractor
surges forward a little faster.  I can feel each distinct switch
taking effect.

However, if I push the pedal all the way down from a dead stop, it
does not immediately jump to the fastest speed - instead it works its
way up through the speeds as if I'd pressed the pedal more slowly.  I
can still feel a "surge" as the 2A contactor closes - even though all
the switches have already been flipped.

Sometimes, when I'm going uphill in too high of a gear, the tractor
will want to stay at the lower speed (unless I press the CC button -
also known as the Power Pulse button - which causes it speed up
immediately).

What's going on?  How does the tractor "know" when it's ready to drop
out the next resistor, if it's not just doing what the switch position
says to do?  I have a schematic (thanks Larry!) and it seems like the
2AH relay and the diode board are somehow involved in keeping the 2A
contactor's coil from being energized, leaving half the toaster still
in series with the armature.  But that's as far as I've gotten...

--Charlie

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