What we seem to have deduced is that the controller and motor are a
matched pair. It seems without doubt that the controller manages the
voltage delivered to both the armature and the fields, otherwise the
"reverse switch" wouldn't be workable. I'd image that the sequence
would be something like:
1) accelerator released: controller ready, no field or armature
2) accelerator depressed: full field, armature current limited,
probably ramping up.
3) accelerator depressed further, full armature current, full field.
This would occur at what I'm calling "idle" speed.
4) at some point, pressing the accelerator further results in the
beginning of field weakening while maintaining full armature.
5) release accelerator partially: full armature current, restore
field current to a greater level. Regenerative braking proportional
to pedal position.
6) completely release accelerator: Well, this is a bit of conjecture.
Dropping the armature at any point during deceleration would result
in the regenerative braking going away all at once, which might be
dangerous if the driver wasn't expecting it, so I'd say that the
controller maintains the armature current until the vehicle has
slowed to the point where regen is weak or nil, probably the "idle"
speed, then it ramps down or cuts the armature current.
All of this is subject to the field voltage. If, like Lee suggests,
it might be a low voltage field, then the controller might have a
buck/boost function for the field, which would complicate our
armchair diagnosis.
I do remember when I was researching the Siemens 1GV series motors
last year during my lithium conversion, I ran across some
documentation that seemed to show some series field windings along
with the shunt/sepex field. The compound field arrangement might be
the key to having stall/low RPM torque available so the motor doesn't
need to idle.
Thinking about it, it's entirely possible that the SCT developers
went with the full-armature/idling motor both because they didn't
want to have to build controllers that could handle the armature
current, but also because that thought that a car that "idles" would
be more intuitive for drivers used to ICE vehicles.
Earlier this month the local utility contacted me about entering my
car in the town's annual Spring parade. I had to decline because
idling at 1,800 RPM in first gear results in a ground speed of 9 MPH.
This wasn't going to work and I was unwilling to ride the clutch for
an hour to keep from riding up on the parade entry ahead of me. Maybe
I should dig that Zilla 1K out of the parts pile and experiment with
armature control.
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