On 8/5/2012 1:13 PM, Jim Coate wrote:
Back when I drove a converted pickup truck with 9" series-wound motor and Curtis controller (1221C?), there was an issue where if coasted backwards and built up a little speed, there would be a sudden lurch. As I understood it, there was enough residual magnetism in the motor for it to generate a little power and as it reached the 0.6 volts of the freewheel diodes they would start conducting and give a little burst of braking.
Could be although in that kind of use it would be quite gentle braking I would expect since the residual field would be small and the speed likewise.
If you attempted to drive it while coasting backwards that would be a different issue. In that case you would be running the motor in reverse. Essentially attempting to plug it. If the controller supports plugging and it is set up correctly that is not a problem. If the plugging is set too high or worse if the controller does not support plugging then you have potential do do serious damage. There is a LOT of torque available in this mode, a series motor that would peak at 100A when started could see 2, 3, 10X that, maybe more and at low PWM. It doesn't take much drive either. I've seen it with PWMs down in the 1/4% range as I recall.
There is a separate set of diodes to support plugging in controllers that support it.
Properly done plugging provides very nice braking (and saves wear on brake pads). It's common on vehicles such as forklifts.
Robert -- From the Divided by a Common Language File (Edited to protect the guilty) ME - "I'd like to get Price and delivery for connector Part # XXXXX" Dist./Rep - "$X.XX Lead time 37 days" ME - "Anything we can do about lead time? 37 days seems a bit high." Dist./Rep - "that is the lead time given because our stock is live.... we currently have stock."