What capacitor to slow down a 52" Hunter Original?

[k4kyv]

I have a 52" two-speed non-reversible Hunter Original ceiling fan (model # 22272), to which I would like to add a 3rd slow speed.

I connected up the motor (no blades attached), and tried placing a 10 mfd capacitor in series with the slower speed winding. That slows it down, but I'm not sure if it would still have enough torque to run if I had the blades attached. I measured the a.c. voltage across the field coils, and it indicates about 60 volts initially, and once it achieves full speed, 75 volts. I think about 85-90 volts would be optimum.

Next, I added an additional 1.5 mfd, bringing the total to 11.5 mfd, and the voltage at the motor increased to 112 volts, hardly any reduction from the full 120 volts without the capacitor, and there is little difference in running speed whether or not the capacitor is in the circuit. I double-checked the capacitors with a capacitance meter, and they all read the correct values. I even substituted another 1.5 mfd capacitor, with the same result. Evidently there is a critical value of capacitance just above 10 mfd, since only 15% additional capacitance makes a tremendous difference in the voltage drop.

I have another fan in the house that is otherwise identical, but that motor came 3-speed nonreversible from the factory. Before I go to all the trouble take down the light fixture to gain access to the switch housing to expose the capacitor in order to read the value (I'm assuming that's where it is located), I was wondering if anyone might happen to know off-hand what that capacitance is supposed to be?

[JW]

10 mfd with the blades attached should give you a good low speed, which I think would be pretty close to the low speed of the current Original. I have a 12.5 for my low speed and it goes about 75-80 RPM, which is what I wanted anyway.

If for some reason the 10 doesn't work wired to the low, try wiring it to the high.

[k4kyv]

Thanks. I'll try the 10 mfd with the blades attached just to make sure it runs OK.

While I had the fan disassembled, I thoroughly cleaned the bearings and shaft using a non-corrosive automotive parts cleaner, soaked the leather and felt rings in mineral spirits, and cleaned out the spiral groove by using a piece of nylon string the same way you would use dental floss. The motor, pulled from years of storage in a basement, was full of black crud, but after I cleaned it and put in fresh oil there is no slop in the rotor nor any bearing noise.

I'll wire the new 3-speed switch so that the first "on" position is fast speed, so therefore the motor will already be spinning by the time it is switched down to the slowest speed.

[Deleted]

I believe 10mfd is standard, but that's from memory, which as we can tell lately, is overloaded.

If you have access to several value capacitors, simply try different values with the blades attached, until you achieve the speed you like. That's what I do.

[k4kyv]

Interestingly, last night I tried the 10 mfd capacitor in series with both the high speed and the low speed windings. It slows way down, but still has substantial torque, with the capacitor on the low speed winding, but using it with the high speed winding, there is hardly any torque, and the fan just sits there and hums. If I manually start the rotor, it might run at 30 or 40 rpm.

Then I measured the voltage across the motor winding. It was only about 20 volts. With the low speed winding, it is about 75 volts. So with the capacitor in series with the line, the fan runs faster with the low speed tap than with the high speed one.

But then that makes sense. I measured the a.c. current with my meter. Without the capacitor, the high speed winding pulls 2.3 amps (without blades), while the low speed pulls almost exactly 1 amp. Since the high speed winding is trying to pull over twice the current, naturally there would be a greater voltage drop through the capacitor.

I believe the series capacitor works exactly like the speed coil in the older fans. In both cases, you are reducing the voltage by using a series reactance to produce a voltage drop. The only difference is that in one case, the reactance is capacitive; in the other it is inductive. This drop produces much less heat than would a rheostat or fixed resistor, because the voltage drop across a reactance is "imaginary", the result of a drop in power factor, rather than resistive, which would be identical to the heating effect of the wire elements in an electric heater.

[Deleted]

Shaded pole motors react differently than PSC motors. I dont know enough to explain why. Brian Hicks might be able to.

I take it your low speed is satisfactory on the 10mfd?

[k4kyv]

I just tried it and the 10 mfd seems about perfect. Now if I can get the blades balanced...