Effective Blower Control
The BLDC control scheme further underscores the technology fit for premix blower applications. For example, consider the following profile.
Some BLDC blower types have been engineered with a simple two-wire control scheme. In these versions, a simple motor controller is “onboard” the motor, and the wires serve as DC power supply connection. The blower’s speed is directly proportional to the supply voltage and a separate speed command signal is unnecessary.
More advanced BLDC blower types incorporate a much more sophisticated “onboard controller.” This allows different speed commands for the blower: DC–high and low voltage; pulse-width modulation (PWM); and mechanically with a potentiometer. The blower speed is directly proportional to this command signal. (In other words, 0 VDC equals zero speed and 10 VDC equals full speed. Likewise, 10 percent PWM duty cycle equals 10 percent maximum speed.) This provides the combustion engineer with flexibility in choosing a blower controller to regulate and monitor the speed of the blower.
The DC signal can be a normal 0 to 10 VDC input or a low voltage 4 to 20 mA speed signal. The low voltage speed command can come from a pressure sensor somewhere in the air circuit and adjust the blower speed command according to the pressure. The blower also can be controlled through pulse width modulation (PWM) and normally is used with the tachometer feedback to confirm the speed of the blower.
The simplest type of speed control uses a potentiometer located on the blower. The combustion engineer can infinitely adjust the speed of the blower without any external controller. This feature is a great asset early in the development of a combustion system and is common for fixed speed applications.
In terms of size and performance, BLDC premix blowers ultimately will offer remarkable airflow delivery in a compact package. As a comparative example, the basic rule of thumb for burner applications is that 500,000 BTUs requires 100 cfm of airflow. By using a BLDC blower, the airflow needs for a 400,000 BTU system can be satisfied with a 5 lb assembly, or just one-quarter the typical weight of traditional blowers.