Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Using the heat when it's cold... mpg drain?

NiHaoMike · 10-22-2009, 09:03 PM

Nowadays, it is common to use electronics to control motor speed, which is very efficient. One easy way to tell is by the presence of a digital control. If it uses buttons or a knob that will turn continuously, it is electronic. PWM is very easy to implement, but inverter drive is the most efficient.

It should be very easy to make a retrofit PWM fan controller. Just a potentiometer varying the duty cycle of an oscillator (~15kHz for high efficiency) and then use a MOSFET and Schottky diode as the motor control stage.

Beware that if you set the fan speed very low with the A/C running, it can freeze the coil and possibly slug the compressor. Therefore, add a comparator to lock out the A/C compressor below the original low speed. One LM339 can operate as the oscillator, PWM comparator, and A/C lockout comparator. Add some resistors and capacitors and a few transistors for the MOSFET driver and A/C lockout relay driver.

10-22-2009, 09:03 PM	#33 (permalink)
NiHaoMike Master EcoModder Join Date: Sep 2008 Location: Texas Posts: 632 Thanks: 0 Thanked 26 Times in 24 Posts	Nowadays, it is common to use electronics to control motor speed, which is very efficient. One easy way to tell is by the presence of a digital control. If it uses buttons or a knob that will turn continuously, it is electronic. PWM is very easy to implement, but inverter drive is the most efficient. It should be very easy to make a retrofit PWM fan controller. Just a potentiometer varying the duty cycle of an oscillator (~15kHz for high efficiency) and then use a MOSFET and Schottky diode as the motor control stage. Beware that if you set the fan speed very low with the A/C running, it can freeze the coil and possibly slug the compressor. Therefore, add a comparator to lock out the A/C compressor below the original low speed. One LM339 can operate as the oscillator, PWM comparator, and A/C lockout comparator. Add some resistors and capacitors and a few transistors for the MOSFET driver and A/C lockout relay driver. __________________ If America manages to eliminate obesity, we would save as much fuel as if every American were to stop driving for three days every year. To be slender like Tiffany Yep is to be a real hypermiler... Allie Moore and I have a combined carbon footprint much smaller than that of one average American...