Delivering Efficiency with Pulse Width Modulation
Efficiency is everywhere. We are constantly being reminded that to be more efficient is to reduce our impact on the planet that we call home. As we have seen elsewhere, a mind-blowing 45% of all energy consumed is used in motors of one kind or another. The size of the opportunity to save energy, increase efficiency and create cost savings is therefore enormous.
Let us use a car engine as an example. A car's engine will produce its maximum power output at a given engine speed. This peak power is generated at the cost of high fuel consumption, and probably a lot of noise. In fact, most car drivers will rarely require this peak performance, and they will use less fuel and inflict less damage on the engine by driving at a lower performance level.
We can compare this car engine to a fan. Fans are designed to provide their peak performance, measured in airflow and static pressure, when the fan's motor is running at 100% speed. Applying the analogy of the car engine, this peak performance will be accompanied by a lot of noise, a high energy consumption, and will certainly do nothing to extend the life of the fan - at full speed, the fan will simply wear out more quickly.
If an application does not require the fan to be operating at peak performance, then slowing the fan down will offer huge benefits in energy consumption, running costs, and the expected life of the fan.
PWM or Pulse Width Modulation, is one method that can be used to control the speed of a fan. This technique works by rapidly cycling a fixed-voltage power supply between the on and off condition, thereby reducing the overall amount of energy provided to the fan. If the frequency of the on-off cycle is sufficiently high, the fan will continue to operate, but at a lower speed.
Fig 1. Chart showing Fan Speed against PWM Duty Cycle
In fact, by varying the proportion of the cycle during which the power is on (known as the duty cycle), it is possible to control the speed of the fan with some accuracy. Fig 1 above is a chart that shows the fan speed of a hypothetical fan when controlled by PWM using different duty cycles. As you can see, the chart is not linear, but by careful selection of the desired fan speed, it is possible to discover the correct duty cycle to use.
Fig 2. Specific Duty Cycles and their effects
Fig 2 above shows three specific examples taken from fig 1. Example C, with a duty cycle of 100% (power on for 100% of the time), will deliver the maximum fan speed, whereas examples A and B show different duty cycles and the fan speed obtained.
Sanyo Denki has release a compact Pulse Width Modulation controller specifically for use with fans, under their San Ace brand. This little controller is designed for use with the San Ace PWM-controlled fans. It can control up to 4 fans at the same time, allowing users to reduce power consumption and fan noise.
The new Sanyo Denko Fan controller is now available from RS Components. Download the brochure here to find out more:
Or visit the RS Components website to buy yours today.
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I notice that this controller box has four different control methods for adjusting the fan speed.
1/ Use an external thermistor to measure the temperature and control the PWM duty, set the target equipment temperature on the control knob
2/ Have no sensor and just manually control the PWM duty from 0 to 100% using the control knob and setting the DIP switch to IA internal adjustment
3/ Connect an external 10K potentiometer to control the speed directly
4/ Connect an external variable 0 to 5V power supply to and change the voltage to adjust the speed
Multi-function PWM fan control all in one unit.