2008-07-24 19:43:39 UTC
A Sepex motor has *one-third* the field voltage rating of a shunt field motor. So regen works down to 1/3rd the full speed RPM's. On the Bombardier and GEM as example (I worked at GE-EV) when you put a silly scope on the field you can see that at full speed the field on the SepEx motor is a 30% duty cycle since it's rated about 23 volts. When you hit the brakes, the field PWM goes up to 100% to 72V momentarily down to about 7mph (notice I said momentarily so the field doesn't burn up).
Then if you want regen to 0 speed (which both vehicles have) you boost convert the armature PWMing a half bridge to boost the voltage back into the battery.
Before I worked at GE-EV I thought (like John) that shunt and SepEx motors are the same but a shunt motor's field is rated for full voltage wheras a SepEx is rated for approx 1/3rd the battery voltage (to make regen easier). That's the difference. In a shunt motor you'd have to *overspeed* the motor to get regen, in a SepEx you don't.
A simple way to get regen on a Sepex (typoically 20A max field surrent) is to get a rheostat trailer electric brake master cylinder, connect to the hydraulic brake and to the field to increase the field current when braking. This will work down to 7mph about.
For an NEV put a MC4013 flip flop efter the speed sensor so it will go about 45mph instead of 25mph (the controller then thinks it's going half speed).
Have a SepEx day,
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