7v / 5v fan mod

pepsi_max2k · Post by **pepsi_max2k** » Sun Dec 23, 2007 6:42 am

Re: http://www.silentpcreview.com/article6-page1.html

I'm thinking about doing this mod for a permanent 5v connection, but just incase it doesn't work...

If I had two 120mm fans set to the 7v mod on two seperate 4pin molexs, and then a hard drive connected to another 4 pin molex on the same stretch of cable, would that be ok?

it would be like this... PSU ... 7v Molex ... 7v Molex ... HD

I'm just worried about that warning that was in there, and I dunno if the HD would suffice for sucking out enough amperage for it not to damage anything...

DreamKiller · Post by **DreamKiller** » Sun Dec 23, 2007 7:15 am

Most or all power supplies only have one single rail on +5V anyway. So basically, the current the fan feeds back using the +7V trick into the +5V line gets fed back to all the devices that use +5V.

pepsi_max2k · Post by **pepsi_max2k** » Sun Dec 23, 2007 7:21 am

erm... is that good?...or bad? i dont really understand all the voltage stuff as you may have guessed

VanWaGuy · Post by **VanWaGuy** » Sun Dec 23, 2007 7:44 am

Pepsi_max,

If you are running 2 fans, if you wire the 2 fans in series on 12V, you will get 6 volts for each. (Less airflow though)

There are serious disclaimers in the 7 volt trick articles. If your fans will start reliably at 6V, I think that is a simpler, and safer way to go.

bonestonne · Post by **bonestonne** » Sun Dec 23, 2007 8:07 am

if you wanted to run you fans at 7v, its fine, i'm running two fans at 7v, have been for a while, no problems at all here.

just plug the fans in to a separate lead. you'll be sending 5v down a rail its not exactly supposed to go to, so you don't want to plug extra hardware there. 5v trick is safer because its just using ground and 5v, 7v is slightly dangerous because you're sending 5v back off the 12v to achieve 7v. could cause major problems.

if you wanted to do something like that, you should just use a fan speed regulator, such as a Zalman fanmate....it would be safer.

Vahan · Post by **Vahan** » Sun Dec 23, 2007 9:24 am

home-made molex to fan adapter

i made it reversible so it can switch teh 5v and 12v rails.
DO NOT connect any non-fan devices into one of these. if you accidentally send 12v to a 5v decive it will most likely explode

the last picture shows how to connect two 12v fans and one 5v fan, in this case it is safe to have another device on the end. if in doubt, even just a tiny doubt, i will not be held responsible for any dead electronics :p

pepsi_max2k · Post by **pepsi_max2k** » Sun Dec 23, 2007 12:12 pm

thanks. just a couple more things...

does it matter where the ground pin is? if i have one in 5v, do i need the ground next to the 5v, or is the one next to the 12v fine to use? just thought it might be important seeings how someone's bothered to put two seperate ground cables there in the first place

and... how would i connect them up in series? preferably without any soldering needed... i only have a pair of tweezers and a 3 - 4 pin adapter... plus one 3 pin/molex fan, and one 2 pin/4 molex fan. with that i can do two 5v mods easy, not sure about much more though

edit: series pics here, and it looks like much more than i have on hand atm: viewtopic.php?t=24148&highlight=12v+ground+wire

bonestonne · Post by **bonestonne** » Sun Dec 23, 2007 12:34 pm

ground is ground, it doesn't matter which you use.

if all you have is pliers and a connector, you could get away with crimping the wires and wrapping that with electrical tape, but you wont want that to be your permanent job.

dhanson865 · Post by **dhanson865** » Sun Dec 23, 2007 4:46 pm

pepsi_max2k wrote:Re: http://www.silentpcreview.com/article6-page1.html

I'm thinking about doing this mod for a permanent 5v connection, but just incase it doesn't work...

If I had two 120mm fans set to the 7v mod on two seperate 4pin molexs, and then a hard drive connected to another 4 pin molex on the same stretch of cable, would that be ok?

it would be like this... PSU ... 7v Molex ... 7v Molex ... HD

I'm just worried about that warning that was in there, and I dunno if the HD would suffice for sucking out enough amperage for it not to damage anything...

If you do the 7v trick it passes through

PSU gives 12v and 5v - 7v mod gives 7v only - the next item in the chain can be a fan wired for 12v and it still gets 7v because the prior fan in the chain is passing 7v out to it on the 12v positions.

Hard drives use 12v AND 5v separately and do not use 7v in any way. If you plug a hard drive into a molex that has been modified for 7v you may destroy equipment and could actually cause a fire if you don't unplug it quick enough.

If you don't have enough PSU molex connections to put the fans on their own lead without chaining the hard drive as well you'll have to get a Y cable. If you have a Y cable it's easier to use the 7v trick on one side of the Y cable than it is to modify the fans. Just leave the fans wired for 12v and use a Y cable with the 7v mod on one leg and be sure you don't plug non fan devices up to the 7v modded connector.

Never use a 5v mod or 7v mod connector on:

A video card
A hard drive
A motherboard (for example ASUS A8N-SLI needs a molex for the extra power on the SLI slots)
Anything other than a fan that actually has logic in its circuitry.

cpemma · Post by **cpemma** » Sun Dec 23, 2007 5:09 pm

A safe (and no-soldering) way to modify the pass-through connector that comes with most fans is shown here. The fan wires are moved, the molex pin voltages stay the same.

A better way to get 7V is to drop 5V across a zener diode; advantage is the speed signal isn't affected, the fan black wire remains at 0V.

pepsi_max2k · Post by **pepsi_max2k** » Mon Dec 24, 2007 2:46 am

thanks hanson, not sure if you understood exactly what i was doing though (hope not anyway...). here's a pic to explain, basically everything's connected to seperate molexes from one psu cable length. i presume it would be ok as currently one of the fans is connected to just 12v and ground, which with your explanation would mean the hd at the end would only get the 12v available to it which obviously ain't happening

all i'm doing from how it is now is switching the fan connector's positive cable from the 12v position to 5v.

dhanson865 · Post by **dhanson865** » Mon Dec 24, 2007 11:02 am

Your drawing is an OK configuration. It was this that had me concerned:

If I had two 120mm fans set to the 7v mod on two seperate 4pin molexs, and then a hard drive connected to another 4 pin molex on the same stretch of cable, would that be ok?

it would be like this... PSU ... 7v Molex ... 7v Molex ... HD

Most fans with molex connectors have a pass through like this http://www.bobtod.com/Overclocking/Pics/Molex7v.jpg

If you connect a 2nd fan to the first fan by way of the pass through you have to leave the wiring standard 12v on the receiving fan(s) and that pass through connection should not be used for non fan devices.

I hope that clears it up.

7v / 5v fan mod

7v / 5v fan mod

Re: 7v / 5v fan mod