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I want to get a larger flow rate out of a common 3 speed induction motor desk fan.
Without forking out for an off the shelf VFD, I thought perhaps I could build a frequency doubler using a bridge rectifier.
Following the circuit from left to right, I'm thinking that I'll feed the 240V mains directly into a bridge rectifier, the full wave rectified output of which will go into a large valued capacitor to block the DC component. I thought that the inductance of the windings should smooth out the sharp bits at the bottom of the waveform, but otherwise I'm open to the idea of adding another capacitor to further filter the full wave rectified waveform into something more sinusoidal looking.
The circuit is complicated by the fact that (I think) the fan has an orthogonal/start shunt winding and capacitor.
Questions:
Can you think of any safety issues with not using an isolation transformer for this circuit, or otherwise?
I intend on measuring the inductance of the windings to choose the correct capacitor values. Will these values change much under load when the rotor is drawing its mutual inductance current?
Is this a viable approach given the additional complexity of the shunt winding? I am yet to fully probe my particular fan, but I've attached a schematic of another fan. I am unsure whether my fan has this many windings, but I know it has one cap.
http://www.electrical-forensics.com/LaskoFan/LaskoFanExemplar/LaskoFanExSchematic-LG.jpg
Without forking out for an off the shelf VFD, I thought perhaps I could build a frequency doubler using a bridge rectifier.
Following the circuit from left to right, I'm thinking that I'll feed the 240V mains directly into a bridge rectifier, the full wave rectified output of which will go into a large valued capacitor to block the DC component. I thought that the inductance of the windings should smooth out the sharp bits at the bottom of the waveform, but otherwise I'm open to the idea of adding another capacitor to further filter the full wave rectified waveform into something more sinusoidal looking.
The circuit is complicated by the fact that (I think) the fan has an orthogonal/start shunt winding and capacitor.
Questions:
Can you think of any safety issues with not using an isolation transformer for this circuit, or otherwise?
I intend on measuring the inductance of the windings to choose the correct capacitor values. Will these values change much under load when the rotor is drawing its mutual inductance current?
Is this a viable approach given the additional complexity of the shunt winding? I am yet to fully probe my particular fan, but I've attached a schematic of another fan. I am unsure whether my fan has this many windings, but I know it has one cap.
http://www.electrical-forensics.com/LaskoFan/LaskoFanExemplar/LaskoFanExSchematic-LG.jpg