Modeling motor control

[Kevin Sevcik]

Originally Posted by Ether

Just to clarify, even with "Forward-Open", the Tan Jag still has a path for the current through the Q4,5,&6 Zener diodes.

Yes, but with a 1V drop, which will drain the current a fair bit quicker. And the more important difference that if your current decays quick enough that you'd start regenerative braking, the diodes will stop that. So the "Forward-Open" mode has an advantage in the (rare) case that a motor is turning fast enough with low enough current that you'd encounter reverse torque.

Come to think of it, this explains Marshal's report of different operating characteristics between the tan and black jags. If you're running the motor at high/full speed and drop to a lower PWM command, the current will decay quicker in the tan jag, but you'll never get reverse torque, so you'll "coast" during the off cycle. In the Black Jag, there's a path for reverse current during the off cycle, so it's possible for the back emf to build up a reverse current and create reverse torque to slow the motor down quicker.

I think this makes sense, but I don't have any simulations set up at the moment to test it.