(ET) Oscilation on the FW dropout circuit

[Christopher Zach <czach computer org>]

Ok, so I finally replaced the flakey card4 with a nice new one. Now I 
have a bit of a problem.

When I power up a hill in speed 8, the tractor of course slows down and 
current goes thru the roof. This causes the current on the shunt to go 
way up, which causes the card 4 circuit to drop power to the FW bypass 
relay.

Thus the relay drops, the FW resistors are shorted and power drops to 
the motor. However this causes the current on the shunt to fall, which 
causes the relay to click back on, which re-engages the FW resistors, 
which causes the current to skyrocket again, etc.

Net result is a buzzing on the relay as it drops in and out which can't 
be good.

Is this normal? I'm thinking of building a lock-out circuit that will 
tie into the other poles on the relay and cause it to stay out if it 
overloads for 5-10 seconds or something. Any thoughts?

Chris