7v from molex

[Hellemyr]

Hi!

From the molex we can get 12v 7v and 5v.

How can i get 7v? And i also have heard that if can be bad for the psu.

I have 1 rail free, and i need to have 2 120mm and 3 80mm fans running on 7v.

The psu i a Hipper Type M 580W

[[XC]melymel]

For 7v, +ve of fan to yellow 12v of molex and -ve of fan to red 5v of molex. I'm not sure on why it's dangerous but I have heard it is too. :toast:

[Sparky]

It is because the 5V rail is sinking current. It isn't a problem on an evenly-loaded PSU though. Heck I've been running a fan in an old system at 7V and the PSU is only some generic 60W or something like that. Came from an old HP machine, it is a uATX PSU, running fold6 in my sig.

[Hellemyr]

What do you mean by evenly-loaded? That all the rails are loades equaly?

But since im plugging 5 fans on 7volt do you think that will be a problem?

[Growly]

By placing a load across the +12V and +5V wires, you're forcing current to pass through the +5V rail backwards. If the current you draw with this 7V is small and you have alot of other devices already on the +5V line, then the voltage drawn by the other devices will be far greater than that created in the opposite direction by the 7V load, and so current flowing backwards won't be a problem. (This is how I understand it, I could be wrong... I saw an article on it once, but that was a long time ago!)

[Hellemyr]

So if i only have fans on that rail that im taking 7v from it will be OK?

[Growly]

Yeah, and as long as you're using the 5V elsewhere also. (Like, on a hard drive, for example.)

[Sparky]

You've got HDs and CD-ROMs that use the 5V, along with the mobo using it so you should be OK. Now if each fan was a delta that pulled close to an amp then I wouldn't run 5 of them, but most fans would be fine.

[Hellemyr]

Ok, i have 3 rails whit a molex plug on. 1 of them is going to the mobo, the 2. is for the water pump and hd and cdrom. And the 3. is for fans and lights, and i have a Y on it, so the lights are on 1 plug and the fans are on the other one.

And since i olny have fan in it, it shud be fine, right?

[Hellemyr]

I tried to run some fans on 7v. I used by "test" psu. A FSP 350W.

So i conect 1 80mm fan to 7v. All fine, it runs good and silent, then i plug in 1 more 80mm fan, both runs good. Then anthoer one, and then the PSU turns itselve off.... wtf?

[Hellemyr]

Ok, did some more testing.

Plugged 1 80mm at7v. And messured whit a voltmeter, 6,58v, ok the psu undervolts abit.

Pluggd in one more 80mm to 7v. Now the voltmeter is showing 4,58v!

Plugged in the last 80mm, 0,58v. Hmmm?

Did some more testing.

Plugged in both 120mm at 12v on another rail, then i plugged in 2 80mm at 7v on a different rail, and the 120mm gets just 10v.

[Sparky]

On your test PSU, do you have anything else besides the fans hooked up? If not, try hooking up some old hard drives, CD-ROMs, or something like that to put some normal load on the 12V and 5V rails. Hard drives would be best, a couple old drives sitting around or something.

[Hellemyr]

When i tested i just havd the 5 fans on.

So i found a old cdrom, plugged that in, and i can plugg 4 fans before the psu shuts down. Then i found a floppy, and then all 5 fans where running on 7v.

SO i got the fans running on my hipper now in the computer now, dead silent. Just too bad the hd is so loud :cool:

[Hellemyr]

7v on the 80mm was abit too loud. So i running them on 5v now.

So i have the 120mm on 7v and 80mm on 5v on the same rail, and all is so far so good.

[ooeric]

just buy a cheap fan controller...
or just solder a resistor onto your fan's line

[Hellemyr]

Fan controller costs money, and i dont have so much of that, and im out of soldering paste:(

But it works fine now, the fans are dead silent and cooling good.