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(ET) Getting around that shunt



Was thinking about the shunt problem this evening. RJ is right; one can't simply bypass it with wire.

But how about bypassing it with a contactor?

This could be a solution: A 100amp soleniod contactor is wired in parallel with the shunt. The rule is the contactor is closed in speeds 1-4, and open in speeds 5-8. Thus when you're tooling around mowing the lawn or getting going the shunt is bypassed. When you engage field weakening, the contactor is open and the shunt rules (cut out FW via the FW relay and the transistors) applies.

The advantage to this is you get to pull full power in speed 4 till the cows come home with nothing in your way. The shunt does nothing till speed 5 anyway, so even if you're pulling a trailer the shunt doesn't matter as long as your in speeds 4 or less.

Now, how do you power the shunt properly?

Here's the thought: The E20 tractor understands the concept of "cruise control" being speed 4 (full power). I spend most of my time there, so there is a vested interest in keeping that as efficient as possible. Speeds 1-3 arent really a problem for me since there are resistors in series with the shunt and the motor anyway, and their resistance (and current drop) dwarfs that of the shunt regardless (think current limiter). So speeds 1-3 don't matter.

The Elec-trak already has a nice little light that tells you when you're in cruise control territory. If I wired the output of that light circuit to a power transistor to either turn on a relay or turn on the solenoid directly I would have it made: The solenoid would bypass the shunt, and the tractor would be able to draw at full power all the way up to motor Etemp.

As soon as you move to speeds 5-8. the CC light goes out. No CC light=no power to the soleniod, and the shunt is in.

Another thought might be to use the other side of the CC relay (it's a DPDT but only one side is used I think) to trigger the solenoid. However that would only work if the CC is on, and I like to drive around in speed 4 explicitly as well. Shouldn't be penalized for that.

What do people think about this?

Chris