writes:

I have this fan I use most of the summer months. It is older than I am
and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
horse two speed motor. That motor eventually burned up. It is now
powered by basically a washing machine motor at 1750 RPM.

The old motor was seven hundred something and eleven hundred something.


My basic idea here is to build a 1/2 voltage and 1/2 frequency
generator to power it at 1/2 it's normal RPM. Power transformers that
will rectify into 70-80 volt rails are out there. I can find them. Then
we are not talking about any class A amp stage here, switching
transistors, driven correctly should do the trick.Thirty hertz, sixty
volts. Would that be efficient ? I don't see why not. I could probably
even find a way to cut back the duty cycle for more savings.

See, I don't need this thing to do 1750 RPM, half that would be fine. I
could easily divide the line voltage and maybe even do it with discreet
components (IIRC how to build a flip flop). Of course now I am dating
myself. You might ignore me figuring I'll die soon, but I assure you I
will never get that lucky. I was meant to live.It is going to get hot,
I am not allowed to die.

Anyway, I used to use this fan in lieu of AC for a long time, only turn
the AC on once in a while since I had it. But that motor is too fast
for it. Looking for cheap and dirty.

My major concerns are starting torque (it has a centifugal start
switch) and if I do have to start it on 120V I will need protection
diodes. Also, should I put some inductance in the path ? or will the
motor windings takre care of that ? I know if I use any capacitance I
need to use inductance, but do I need any capacitance ?

I don't see any reason to screw around with waveshaping for a coil the
is going to turn a shaft, do you ?

A lot easier to just find a two speed motor surplus.

If you use a class A amp, anything you save on electricity to the fan
will go into the amp transistors. :-)

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