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Reducing Fan Speeds

Fan Voltage Calculator


Reduce  volts,  amps, to  volts.  

Original fan voltage: 12V

Original fan current: .2A

    V=IR (Ohm's Law), so 12 = .2R   =>   R = 12 / .2   =   60

Fan resistance: 60 Ohms

Target voltage: 4.5V

    V=IR (Ohm's Law), so 4.5 = 60I   =>   I = 4.5 / 60   =  0.075

Target current: 0.075A

Voltage drop across resistor: 12V - 4.5V  =  7.5V

    V=IR (Ohm's Law), so 7.5 = 0.075R    =>    R = 7.5 / 0.075    =  100

Target resistance:  100 Ohms

Power dissipated by resistor:  7.5V * 0.075A  =  0.563W

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