Kirk Wallace wrote: > > I haven't looked at the control signals with a scope. One inductor was > much hotter than the other. I assumed because it was because I was > driving the motor mostly one direction. I was planning on using 110 > Volts for the motor supply. > Hmm, synchronous antiphase would have both inductors equally hot. A lot of PWM jitter in one direction could heat the one giving the positive output more. The heating is worst at 50% on time. > I am not sure what you mean, but I get the impression that you are > saying that for synchronous anti-phase, the PWM signal and the direction > signal are both modulated to control motor speed? No, PWM is just turned on 100%, and the only signal that is changing is direction. This would make it work like the output stages of a Gecko 320, for instance. I did put a voltmeter > on the direction signal and got 0 and 3.3 Volts DC with a direction > change. The PWM signal went between 0 to 3.3 Volts DC dependent on the > speed setting. There was never any audible noise from the motor other > than bearings and brushes, which actually was kind of strange. After looking at the Pluto blurb on their web site (a bit sketchy) it seems like sign/magnitude is the default, they call it pwmdir, I think. I am > feeding the spindle command straight into the Pluto PWM input, so, I > believe, there is no PID or anything else that could be tuned. I am a > little surprised the Pluto PWM frequency isn't higher. > Hmm, this is a strange problem. First, I don't think you will get very good speed control without a control loop, unless the motor resistance is very low, but second, I don't understand the heating. At 19.5 KHz, the output current will be discontinuous, and that will cause some slight increase in iron losses in the inductor. Maybe if you were testing mostly at half speed, that would put the PWM duty cycle at 50%, the worst case. What is your DC supply voltage?
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