Power resistor help (novice)

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ZapbuzZ
Posts: 3
Joined: Tue Feb 27, 2018 10:57 pm

Power resistor help (novice)

Post by ZapbuzZ » Tue Feb 27, 2018 11:05 pm

Hi.
i have 10 x 12v 0.14amp computer fans i need to quieten down.
What I want to do is splice 1 of their molex cables 12v line to include a resistor to decrease the voltage from 12 volts down to 9v.
basically its 10 fans plugged in together making a total of 1.4 Amps @ 12 volts.
I was thinking of using a 2 amp resistor but I do not know what kind of resistor or value to use.
Can someone tell me please and tell me if there's a calculator for this kind of thing.
Thanks. :D

David
Posts: 172
Joined: Sun Oct 04, 2015 6:18 pm

Re: Power resistor help (novice)

Post by David » Wed Feb 28, 2018 7:00 pm

This is an exercise in Ohm's Law, and there are calculators for this (and many other things) on this site. Look at the LHS of the banner at the top of this page.

You need a resistor which will drop 3V at 1.4A. The nearest value is 2.2 ohms, and resistors with this value are easily available. it will be passing a current of 1.4A, and therefore will dissipate 3 x 1.4 = 4.2 watts. You could use a 5W wire wound resistor, but it would get hot - it would be better to use a 7 or 10W one and the price should not be excessive. Make sure that the heat from the resistor does not affect anything in the vicinity. You could use 10 x 22 ohm 1 W resistors in parallel or one for each fan if you wished.

ZapbuzZ
Posts: 3
Joined: Tue Feb 27, 2018 10:57 pm

Re: Power resistor help (novice)

Post by ZapbuzZ » Thu Mar 01, 2018 2:27 pm

@David Thankyou for your guidance.
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