Ok, first the results, then the analysis:
Code:
Value (ohms) Measured mA@12V Notes
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680 678 230
820 818 210
1200 1184 170
1200+180 1363.6 150
1200+180+2.2 1366.6 150
1200+180+10 1374.3 150 Hung at 140 mA then stayed at 150 mA
1200+180+15 1379.4 150 Low resonance once spinning, spun up to high RPM; 120 mA with load
1200+180+22 1386.6 190 Weak resonance, low pitch, spun up to low RPM
1200+180+33 1397.1 190 Resonance, lower pitched, spun up to low RPM
1200+180+39 1403.3 190 Resonance, lower pitched, spun up to low RPM
1200+270 1452 Resonance, lower pitched, would not spin up
1200+390 1584 Resonance, lower pitched, would not spin up
1800 1784 370 mA resonance seen, went negative (!) amps, no resonance after that; would not spin up
2700 2680 Resonance, higher pitched, would not spin up
.
It was pretty surprising to find self-resonant behavior--I can see how people could get distracted by it.
It's also easy to see why the coil resists the rotor in that mode, since the circuit no longer self-regulates at that point. The rotor would have to be turning at the resonant frequency to stay spinning!
My meter can only measure down two significant digits at these amperages, so I'm pretty sure there's some differentiation at those levels marked 150 mA. In particular, I'm thinking that 1374.3 ohm is probably closer to 150 mA than the other values.
I'm also finally seeing the 'shifting into high gear' phenomenon that you were talking about, Aaron, with the power consumption going down as the RPM goes up.
It seems tuning is the key here.
