View Full Version : 12v to 5v on the fly switch

04-07-2009, 10:01 PM
here is a simple way to switch from 12v to 5v mainly for your fans. i use it for benching so i don't have to pull the molex plug out and take out my adaptor. instead i just flip a switch and i'm good to go :)

wiring diagram


and here is what it should look like when soldered up


and here are the switches installed to control the fans on my 2 rads.


think thats all i need to explain it, if not tell me what i need to add, or any questions you have.

i know people ask about it so hope it helps.

i added diagrams for a 5v,7v,12v setup as well as a 7v, 12v setup.

12v and 7v and 5v switch

as for the switches you would need 2 of them to get 5, 7 and 12 volt options. they would have to be double throw single pole or double pole double throw.

here is a wiring diagram to do it. note the legend

black wire = ground
red wire = 5v line
yellow/green wire = 12v line


here is a better picture.


- you split the 5v line to 1 side of both switches.
- on the first switch you run the middle leg to the fan's red/power wire.
- you either join both ground wires at the molex, or just use 1 of the 2 grounds.
- run a wire from the ground (black wire) of the fan to the middle leg on the second switch.
- run the ground wire to the last leg left of the second switch.
- run the 12v power line to the last leg on the first switch.

that will get you the 5, 7 and 12 volt options.

now, here is a disclaimer
when you want to run 7v you need to first set the fan to run 12v. once that is done then you can set the second switch to 5v. if you try to change to 7v operation while the first switch is in 5v then you *could* damage the fan since you would be feeding 5 volts to both sides of the fan. i personally think the fan would just stop running, but i cant say for sure or guarantee it's safety. so i am not responsible for anything that goes wrong. though i highly doubt anything will.

12v and 7v switch

looking at it again you can pull off a 12v and 7v switch with the following diagram.

yellow is 12v
red is 5v
black is ground

red to fan is positive
black to fan is ground (negative)

if you can't figure it out just let me know, it's a bit messy but hopefully you will see where the wires go.

when and if you try this make sure the 2 sides of the switch are not connected. by that i mean it's like 2 switches in 1. i'm 80% sure that any switch that says double pole double throw is separate.

01-01-2010, 07:08 PM
just a fyi guys/gals i updated this faq and will work on it some more a bit later on.

10-19-2010, 11:11 AM
Hello Spawn-Inc,

Thanks a lot for posting such a detailed pictorial guide. It is very helpful.

I just made one 12v-5v switch last night:). But I still have problems with soldering, as this is my first experience with the process:alien:!! So I unsuccessfully 'partially' soldered one wire and for the other two terminals I just put the wire through the hole in the prong and twisted them off so that they'd just hold. I put sleeves on all of 'em.

I tested it on a case fan and it works like a charm but I am currently not using it because I feel the joints might not be strong enough when not soldered.


I'm planning to make three or four switches and bolt them on to a spare 5.25" bay face plate as I need to have easy access. I also have an idea to fix the switches on a plate covering the empty PCI slots, so the switches are out of sight but still accessible.

As of now, all case fans (one 90mm under the HDD, two 80mm side fans and one 80mm exhaust - which will soon be replaced with a 120 mm Cooler Master) are voltmodded to 5v.

I need to put the switches in because the HDDs reach or exceed 40 C (103 F) when the air conditioner is off (when I am not in the room) and I can afford to run the fans (screamers!) at full speed (12v) only when I am not around.

10-19-2010, 11:52 PM
nicely done, looks alot more pro then mine do :)

do you have any flux or soldering paste? if so then get a tooth pick or something like that and put a little on the wire once you have put it through the ring on switch like you did. put the iron on it and it should help the solder flow nicely.

11-18-2010, 05:48 PM
Awesome guide.:).

I went with the 12v & 7v & 5v DPDT on the fly mod switch.
My soldering gets better closer to the third set.

Thanks for the Diagram.

First set.

Second Set.

Third Set.


Finished results.


11-19-2010, 02:11 AM
nicely done! are you going to label them or just remember and confuse others lol

11-19-2010, 06:06 PM
Nice! This is exactly the final design I had in mind. My soldering did get better finally :) But I haven't installed the switch yet, just made a prototype. For now, I'm now planning to put a zener diode in series with every case fan that needs slowing down. I might add the switches later if I require variable voltages.

11-21-2010, 09:31 PM
nicely done! are you going to label them or just remember and confuse others lol

Well, I know em by heart. pretty simple. Take a look.

First 2 switches control my two front fans, the second two switches control my HS fans "push/pull" and my exhaust port fan on the back of the case then the third two control the fan at the bottom of my case as well as with the side fan on my case.

I also spent a day redoing the wires, I have made them a whole lot shorter, removed the trailer clamps, blue double end connectors and also removed those red male/female plugs and soldered the wires together & heatshrinked em. Looks even better now than before & also fits better in my case. At the time I didn't get any photoshots on how it looks now but will in the future when I take it back out.




11-25-2010, 06:50 PM
Are those grill plates standard drive bay covers? If so, where did you get them, Twisted?

11-26-2010, 09:55 AM
Are those grill plates standard drive bay covers? If so, where did you get them, Twisted?

Yup they are standard 5.25 bay covers.
Mine came with my antec 900 case but you could buy Lian Li bay covers. Also if you are wondering, I created the mounting holes on the bay cover for the switches. I driller the mesh with wood underneath, took a dremel, knocked off the slivers then the mesh was kinda bent from drilling so I used the flat end of a ball ping hammer, slightly lightly tapped the mesh on the end of the vice which has an anvil. Came out nice looking.

Here's the link for Mesh Lian Li bay cover.

frozencpu might be a bit more expensive, you might be able to find them cheaper some where else.

11-26-2010, 10:28 AM
Aah, thanx. I don't plan on mounting any switches, but the conductive shielding, airflow, and lighting leakage would all be handy for what I have in mind.

Hehee, antec and lian lay bay covers, I didn't know you could buy 'em separately, how foolish.