|Hey folks! Working on a Robbins & Myers Hunter pedestal fan motor for a friend. It's the same one which I replaced the exploded capacitor in a little while ago, on this thread: http://www.afcaforum.com/forum5/48939.html
You might remember, I tried to replace the Levolier switch with a thyristor type Lutron speed control. It worked, however the motor would draw very excessive amps and overheat when it was reduced in speed this way.
In talking with some folks, I found out that someone has already found a way to get around this. You can use the Lutron control to slow the motor down, when it is in Low speed mode. In other words, when the motor is wired for High speed, it is not compatible with the Lutron control. When the motor is wired for Low speed, it IS compatible with the Lutron control.
The fan I was shown, had two controls. One was the rotary knob for the speed control. The other was the original switch to select High or Low modes. When it was in Low, the variable speed was active and usable. When in High position, it was always full voltage.
I wanted to replicate this design, but using only one control, without drilling any new holes. To do this, I located a pushbutton High/Low/Off switch; as well as a Lutron dimmer with a push-on/push-off function. In other words, you rotate the knob to vary the intensity of the light, but push the knob in to switch the light off and on.
After dismantling this dimmer I found it easy to remove the original on/off switch. I was able to adapt the Off/High/Low push switch to the dimmer in its place.
After that, it was a simple matter of wiring the "low" circuit through the dimmer, and to the motor's Low winding. The wire from the switch for High went directly to the motor's High winding, bypassing the dimmer.
In order to prevent the dimmer giving the fan an excessively low voltage where it wouldn't turn at all, I put a bypass resistor in the circuit of the control, so that even with the knob at full minimum, it still will pass enough current to make the motor run.
Here is a picture of the modified Lutron control in the back of the motor cover.
And a picture of it with a vintage bakelite knob in place:
There are a lot more details in the video that follows!