SPCR

Good day to you all.

I was wondering: If I connected a fan to a 12 V header but with two 12-to-7 V resistors in between.. How much will the fan then be fed with in terms of voltage? How would you calculate that?

Thanks in advance.

Hi,
If the "resistors" are real resistors, than you can use U = RxI to determine what voltage will be applied...but if you don't have the resisotrs value (it is often around 56 Ohms), that won't help

kuzzia wrote:Good day to you all.

I was wondering: If I connected a fan to a 12 V header but with two 12-to-7 V resistors in between.. How much will the fan then be fed with in terms of voltage? How would you calculate that?

Thanks in advance.

I would highly recommend Zalman FanMate-2 or a fan controller instead.

Lithium466 wrote:Hi,
If the "resistors" are real resistors, than you can use U = RxI to determine what voltage will be applied...but if you don't have the resisotrs value (it is often around 56 Ohms), that won't help

Actually, you don't need to know the resistance, you only need to know the ratios. In this case, one resistor gives 7V across the fan and 5V across itself. Two resistors therefore gives (7/(7 + 5 + 5)) * 12 ~= 5V across the fan.

That's assuming the resistors are in series. If they are in parallel then it will be (7/(7 + (5/2))) * 12 ~= 9V

Thank you for your answers.

They are in series. I use these:

http://www.quietpcusa.com/Zalman-RC56-7 ... -P102.aspx

Perhaps I'll invest in a fan controller, though I would prefer an ASUS motherboard with one PWM header and two 3-pin fan headers. I quite fancy their fan controlling and automatic fan controlling in general.

These are 56 Ohms