I am making a power supply and control circuit for this high-power brushless brushed DC blower fan. It is said to run at 9.4A at 12V DC, so it presumably has a resistance of 1.276Ω, and consumes 113 watts of power at full load.
I am using a transformer to step down the 60hz, 120V AC mains power to an appropriate voltage. But the problem I see is that single-phase AC does not supply continuous power; it goes past 0v every time it changes direction (120 times per second). A bridge rectifier would turn this into a pulsating current/voltage. But how can I maintain a fairly constant voltage at such high power draw? A constant (rather than pulsating) voltage would probably result in less wear to the motor, less noise, and more predictable behaviour.
Here are the solutions I can think of to supply a large constant direct current from an AC source:
I am using a transformer to step down the 60hz, 120V AC mains power to an appropriate voltage. But the problem I see is that single-phase AC does not supply continuous power; it goes past 0v every time it changes direction (120 times per second). A bridge rectifier would turn this into a pulsating current/voltage. But how can I maintain a fairly constant voltage at such high power draw? A constant (rather than pulsating) voltage would probably result in less wear to the motor, less noise, and more predictable behaviour.
Here are the solutions I can think of to supply a large constant direct current from an AC source:
- Polyphase (eg 3-phase) power source and rectifier.
- (This option is not available to me.)
- Single-phase transformer and rectifier with huge capacitors.
- According to my simulation on LTSpice, it will take 14mF of capacitance to stop the voltage from going below 2/3 of the peak. The capacitors should have a high ripple current rating.
- Rectified single-phase with huge inductor.
- This inductor would be quite huge. Actually, this method does not work at-all according to my simulation.
- A combination of huge inductor and capacitor.
- I have heard that inductors combined with capacitors often have oscillation currents. Would this be a problem even if I had a diode between them?
- Using a transformer with a higher output voltage and stepping down the rectified voltage using PWM (when the voltage is more than 12 volts). A more modest-sized capacitor can be used for when the voltage dips below 12V.
- I would need a PWM control that works with a pulsating input voltage. The fan I'm using is not said to be rated for PWM, but I'm guessing it would be fine if I use some good capacitors to absorb the voltage ripple and an inductor.
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