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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
How feasible would it be to control a BLDC motor using nothing but transistors/comparators/op amps? I have a motor that outputs digital highs and lows for the sensors and was thinking I could use those to directly control the motor. Would this be more reliable than setting up a microcontroller? I need this motor to run when power is applied 100% of the time as it will be running a pump for a computer water cooling system. Thanks! -Jesse
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
The best thing for your application would be to buy a cheap BLDC motor controller like the ones used in RC models.
In my limited experience, those require a control input like that from a RC receiver: a stream of pulses whose width indicates the throttle setting. I substituted a 555 and a potentiometer. Complication: my BLDC controller won't start before it detects a valid control input, whose pulse width is in the range for zero speed. Then it indicates "ready" by making the motor generate some beeps (which would augment your computer's acoustic signature when it starts up. )
Back to question in OP: sounds like a good project. There is a low-speed operating range where you can run the motor like a stepper, without feedback. Just cycle the stator phases, and the armature will follow.
"Mag drive" hydroponic/aquarium pumps have permanent magnet rotors, and perhaps use cheap shaded-pole or capacitor-run AC stators instead of switched DC.
Submersible pumps sold for tabletop fountains are even cheaper, I bet using shaded pole stator with induction or PM rotors:
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Discrete BLDC Motor Control
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