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Fan switch plan, advice needed

G

Grammar Nazi

Limp Gawd
Joined
Mar 9, 2003
Messages
282
Here is the plan:

I have all my fans in the case (excepting the CPU) on one power supply cord. What I want to do is grab a molex extension plug and modify it with a switch that will take the ground wire and pass it through as normal in one position, and in the other position will instead feed the 5v line in the ground line's place. I would then drill a small hole or some kind of mounting hole in the side of the case or an empty 3.5" bay and place the switch. Then, I can choose to have all my case fans running at 7v or the regular 12v if I like.

Here is the reason:

I am a cheap bastard that doesnt want to have to buy a fanbus, and this would do what I wanted anyway.

Here is the question:

Will this screw anything up if I try it? I am an electronics newbie, and for a minute while I was concocting a plan I thought I could just cross a wire from the ground onto the 5v line... but I then realized that would probably fry my power supply/motherboard somehow. This is the kind of fuckup that I am trying to avoid.

Thanks for the help.
 
I did that for about 4 fans with one switch.

Nothing caught fire or exploded so I think it's safe.
 
How many fans are you planning on hooking up to this switch? The only problem you might run into is drawing too much current through the single molex wire and switch.

Check on the labels of your fans for how many amps they draw. It'll be the number with an A after the number. Add these numbers up and that will be the total number of amps you'll be drawing. You'll have to make sure that you get a switch whos amp rating exceeds that amount. That's the only thing you'll have to worry about. :cool:
 
alright, cool. I was figuring that it didnt matter if I had the fans all on seperate power supply cords because they are all just splitting a single signal. It's going to be up to 4 80mm, 1 92mm and 1 120mm fan in the future so that should be around... 2 amps if my math is correct.
 
alright, someone who knows anything about electronics should be able to help me since I do not:

I got a switch called "DPDT", is that what I want? It needs to have one output slot and two inputs from which it will choose, I dont want a switch that is just on and off
 
The switch will work fine, DPDT stands for Double Pole Double Throw. All you really needed was a SPST (Single Pole Single Throw) switch. A DPDT switch is like two SPST switches in one package.

...

The other set of terminals can be used to switch something else if you'd like
 
heh, I figured that part out slowly but surely. I think what I actually wanted is a SPDT switch, because I want to have it choose from a choice of 2 wires to place into one output wire.

it looks like this, and works great except I am really shitty at soldering and its likely that the connections will touch if it bends a bit.. hopefully I can find some way to insulate the seperate terminals.

Untitled-2.png
 
oops when I said SPST I actually meant to say SPDT :rolleyes:

But yeah you got it right, to keep the wires from touching use some heatshrink tubing to insulate your connections
 
ordinarily I would, but this is an extremely tight space and I am unable to get the tension I want in such a small space with duct tape.
 
in case anyone was curious, I now have it set to make the fans either 5v or 12v and every fan in my case is hooked up to it, which means 2 cooler master LED fans, 2 SVC 80mm fans, and a panaflo Silent Boost fan. Now all I need to do is find a way to quiet those damn hard drives.
 
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