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issue: February 2003 APPLIANCE Magazine

Motor Technology
Variable Speed Controller for Air-Moving Devices

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Varidigm Corporation (Plymouth, MN, U.S.) has introduced the VSM-CA3 variable speed motor controller, which is used to modulate the speed of motors in fan coil units, fan-powered VAV terminal units, fan filter units, and other air-moving HVAC devices.

According to Varidigm, its patented VSM-CA3 controller can solve some of the issues related to dimmer-type switches such as heat generation and noise.

The VSM-CA3 controller provides modulating control of a.c. induction motors in response to an analog input signal from building automation systems, thermostats, or other control devices. It provides continuous motor speed in response to 0-10 V d.c. or 4-20 ma d.c. input signals.

The patented controller receives the signal and responds by adjusting the fan motor speed. The VSM-CA3 is said to be capable of modulating the fan motor to a speed just one-fourth the rated maximum speed. This turn-down ratio is said to be far greater than has historically been feasible with a.c. motors controlled with either three-speed or dimmer-type switches.

"Other people have been modulating commercial air-moving devices like fan-powered VAV boxes, fan coil units, and ventilators for years using dimmer-switch type controllers," explains Mike Woolsey, commercial sales manager for Varidigm. "But there's been a common thread of complaint with the fact that the dimmer switches seem to shorten the motor life, and they also don't have a high enough 'turn-down ratio,' which is how far off the maximum you can slow down the motor. For example, a 2-to-1 turndown ratio represents a 50-percent reduction in speed. Our product is capable of a 3-to-1 ratio, which is probably its greatest benefit, but it does it in a way that overcomes the issues with the dimmer-switch type controller. That is, it doesn't generate as much heat and is quieter. Another feature is that it doesn't cost as much a variable frequency drive."

According to the company, with the VSM-CA3 controller, when a fan motor slows down, energy savings occur. This, in turn, reduces the operating cost of the HVAC equipment in which the fan is installed. In addition, the controller reportedly allows building owners to increase occupant comfort by dramatically reducing the draft felt by occupants. The soft start and soft transition between speeds also reduces the noise generated by the fan.

The major design benefit of the controller is its heat reduction compared to dimmer-type switches. "The dimmer-switch method uses a single triac, which is a device used to 'chop the wave.' In other words, instead of sending a pure sine wave to a motor, it will just 'chop the wave' - cut it off at its peaks and valleys - so that it doesn't get as much power to the motor," Mr. Woolsey tells APPLIANCE. "When you do that you create harmonic distortion, which is really the motor's response to getting something other than a pure sine wave, and that causes heat and can also cause an audible noise or a hum," he explains.

"Our product utilizes a patented method of using multiple triacs and a novel way of wiring a motor so that we can send a 'chopped' wave into only part of the motor instead of the entire motor," Mr. Woolsey continues. "That allows the motor to run more smoothly, with a better signal going to the larger part of the motor. The end result is less heat generation and less sound."

The controller is UL-/CUL-recognized and is designed for use with Varidigm Definite Purpose Split Capacitor (PSC) Frame 42, Frame 48, and 3.3-in motors ranging from 1/20 to 3/4 hp. The controllers are available for 120-, 240-, and 277-V, 60-Hz motors.


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