Topic: cheap electric fan control?

[booger1]

i have a 16in fan i bought from autozone a few months ago. it works great, but is really loud and sounds like a leaf blower when i turn it on ( mostly in the line at mcdonalds)  is there a cheap way to turn the fan speed down without buying a expensive fan controller?  maybe a windshield wiper switch or a rheostat?   it said on the box it was supposed to be very quiet and it is until it winds up to full speed. it has only 2 wires on it

[emsvitil]

Some high-wattage resistors....

Some of the setups for stock electric fans are 2-speeds.   The slow speed runs thru a resistor.

(I know ford focus's do this)


Lets say your fan is running at 14volts, 14 amps.    (196 watts, 1 ohm resistance for fan)

A 1 ohm resistor would reduce this to  (14v/2 ohms = 7amps).  14v is split between fan and resistor; so fan would use 7 volts & 7 amps  as would the resistor each would use 49 watts ( 7* 7)

The resistor would have to handle 49 watts.... and the fan might be a little slow

Let's try 1/2 ohm resistor....   (14 / 1.5 = 9.333 amps)   Fan would be 9.333v   * 9.333amps = 87 watts.   Resistor would be 4.6666v * 9.333amps = 43.55 watts.  (Fan voltages is 1/1.5 * 14v)

Still think fan would be slow

Now lets try 1/4 ohm   (14 / 1.25 ) = 11.2 amps.   Fan 11.2 amps * 11.2 volts = 125 watts

Resistor 2.8v * 11.2 amps = 31.36 watts.   (Fan voltage = 1/1.25 * 14 volts)


This might work,

So get 2 packs of this:

http://www.radioshack.com/product/index.jsp?productId=2062290&filterName=Category

and run in parrallel for 1/4 ohm resistance 40watts capacity.   (note: they'll get very hot)



Measure the voltage and amp draw of the fan  and change above to figure out what you need.


You'll probably want a way to apply full power  (AC trips a relay, high heat trips a relay; bypassing resistors)

[booger1 [OP]]

cool, thanks