Reduce DC Fan speed via resistor.....need a bit of help

[thirdlegstump]

Hey guys, I have an external drive exclosure that's a bit too loud for my tastes.
There's a 12VDC .07A fan in the case and I'd like to reduce it's speed to about half.
What kind of resistor do I need? Can I use something I grabbed from Radio shack?
It's been awhile since I did any electrical study.

Thanks.

 

[Zepper]

The formula is: Edit (sorry, brain fart): I(A)= E(V)/R(ohms). That will tell you the R of the fan. Most 12V fans will run on from 7V to 12V. So you need to get a variable resistor that will allow you to work in that range. (resistor needs to cover the range from 1/2 of fan resistance down to 0 ohms)
.bh.
Almost :beer: time!

 

[sanaka]

It's: V = IR

As in: Voltage equals Current multiplied by Resistance

NOT: V = I/R !!!!!!!!!!!!!!

Peace
Sanaka

 

[HiTek21]

You can try a 3w Wire Wound Rehostat from radio shack. I have one wired into my 120mm Panaflo and works great, however your fan might stall if you turn it down too low.

 

[scdill]

Originally posted by: deathkoba
Hey guys, I have an external drive exclosure that's a bit too loud for my tastes.
There's a 12VDC .07A fan in the case and I'd like to reduce it's speed to about half.
What kind of resistor do I need? Can I use something I grabbed from Radio shack?
It's been awhile since I did any electrical study.

Thanks.

If the specified .07A is accurate, then the fans DC resistance is about 170 ohms. So:
- A 50 ohm resistor should drop the voltage about 2.7v.
- A 75 ohm resistor should drop the voltage about 3.7v.
- A 100 ohm resistor should drop the voltage about 4.4V.
- A 125 ohm resistor should drop the voltage about 5.0V.
- A 150 ohm resistor should drop the voltage about 5.6V.

Some 12V fans require 7V or more to start.

 

[Mday]

get some low OHM resistors, and wire them up in series till you like it. or get a medium OHM resistor and wire them in parallel 😉