AC Motor Speed Control with BS2?

CJC504

For the BS2, is there an easy/cheap way to modulate a 120V AC motor that draws approximately 0.35A? The motor does not need to run for a very long time (maybe 2 hours total, but not continuous) so I am not very concerned about the life of the motor or efficiency. Also, the motor does not need to be able to be reversed. I am just trying making a small scale VAV system where the fan (AC motor) speed modulates based upon the static pressure inside of the supply air duct. The fan would ramp itss speed up and down to maintain a static pressure setpoint. In commercial applications you would typically use a VFD or VSD to modulate a 3 phase motor, however, I am building this model at my house so I need something cheap and simple. I tried replacing the fan motor with a DC motor and I used the HB-25 to control it, but I could not get enough power because of the DC motor and HB-25 voltage limitations.
Is there a way to wire connect the BS2 to a rheostat or fan speed controller? Perhaps replace the manual potentiometer with a digital potentiometer? Any help or other ideas/suggestions would be appreciated. Thanks.

Chris

Mike Green

I would get a suitable AC motor speed controller (for the fan you intend to use) that has a knob on it. I would get a servo motor with a 360 degree rotation (called a "sail winch servo" like this) and fasten it onto the knob to turn it. There's lots of documentation on how to control a servo motor with a BS2. The reason for doing this is safety. You're dealing with power line voltages. You could certainly build a triac-based speed controller with an optically isolated digital potentiometer, but you'd need to know what you're doing.