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Old 03-27-2012, 03:33 PM   #44 (permalink)
mechman600
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Sepex motor research nerd

Needless to say, I have done a whole lot of research on sepex motors over the last week or so. Sepex = separately exited field. The field is wound much finer than a series wound motor, requires much less current and it separately controlled from the armature.

Sepex motors have many advantages:

-Much broader RPM range. With a constant armature current, the more current you feed the field, the more torque will be produce but at a slower speed. The less current you feed the field, the faster the motor will spin but with less torque. A proper sepex motor controller with proper field mapping will give the field more amps at low speed for more torque, and as the motor speeds up it will reduce the field strength for more motor speed, thus broadening the "power band."
-Regen braking. Many controllers can simply reverse the armature while keeping the field the same (or vice-versa). However, this only works well in lower voltage applications where the brush timing is neutral or close to it.
-Reversing. Basically the same as regen braking.

Sepex motor disadvantages:

-Proper motor controllers are more expensive
-Controllers of high voltage are hard to find. Generally, 72V is as high as you can go.

So where does that leave me? We'll see what this "field control module" looks like from EPC corporation. I hope it can handle a wide range of voltages, not just 12V. What I envision is controlling the field through two "taps" in my pack (maybe 12V and 24V or 24V and 48V) through two relays and a double throw switch. This would be my electric "gear shift". The higher field voltage would be used to take off from a start and the lower voltage once it revs up past a certain speed. All in conjunction with my PM/series motor controller.

Even if this field control module is junk, I only need it to suppress the giant voltage spike when I open the field circuit. Could this not be accomplished by simply wiring a large capacitor with the field?

All this might have ended up being a good thing.
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