Driver current in steppers

Hi Bill and the List,

For an experiment, I connected a 12V auto (US) brake light in series
with the 45V motor power supply to my new/used Centent, er, Gecko
microstep driver. This doesn't appear to affect the motor's operation
at all! You can thus watch the current drawn by the driver, and it
affords some protection in case of a wiring short. 2A current set, 350
oz/in 3.43V, 3.3A NEMA #23 SloSyn stepper (yes, I'm only running 2A).

I haven't "calibrated" the lamp, but I can see the idle current (quite
low), and as the motor accelerates, the lamp quickly goes out! (quite
low current). At high speed, there is little or no current drawn! Love
those choppers! NOTE: motor on desk, no real load, even when I tried to
hold the shaft with my fingers.

The lamp seems to have no affect on the motor operation! I put it in
the circuit to act a "fuse", in case there was a short in the motor,
wiring or driver. The theory being that a short will not "smoke" the
driver! In the past, I've used it when building discrete PWM driven
H-bridges for my robot. With the current limited (the lamp), the
circuit can be checked out with less risk.

So I take it full current is not needed all the time (yeah, I knew
that). And if I had a short, the lamp would limit the current to a
safe(r) level, glow brightly, and burn out if necessary. Then there is
also the "cold vs. warm" resistance of the filament (whatever that
does).

No real loads, so maybe this test isn't relative to anything. When the
motor is drawing heavy current, the lamp should drop some of the
available "headroom voltage", and reduce the possible acceleration.
What else will it do?

Alan KM6VV