12v to 7v conversion

[maniac]

So guys I was thinking of making my rig a bit more silent. I am currently running 7 out of my 8 fans over the fan controller thingy that came wih the switch 810. Like this.

If I remove the two black cables in the molex connector, will all the fans connected to it be running at 7v?

ps. don't worry I will use a (very) short molex extension instead of cutting the lead coming from the psu.

 

[jamesriley94]

I've done the same thing as you're suggesting, but no.

You need a small molex extender, then looking from the pictures point of view:

-Remove the 2 wires on the right hand side - black and red.
-Swap round the remaining black and yellow, and move the yellow into the post at the other side.

So you know - look on the PCB of the fan hub, and you'll notice that only 2 of the pins on the thing are actually wired to the fans.

 

[maniac]

I've done the same thing as you're suggesting, but no.

You need a small molex extender, then looking from the pictures point of view:

-Remove the 2 wires on the right hand side - black and red.
-Swap round the remaining black and yellow, and move the yellow into the post at the other side.

So you know - look on the PCB of the fan hub, and you'll notice that only 2 of the pins on the thing are actually wired to the fans.

you lost me there mate I will be using a molex extension, do you mind sparing a couple of seconds for me and do a rough sketch on paint on how the cables need to be wired.

Thanks in advance,
maniac

 

[jamesriley94]

That will probably confuse you more...

Only 2 of the connections on the fan hub themselves are actually wired.
That means, to make the fans work, 2 cables have to go into those connections. Therefore you have to rewire it from the PSU end rather than the connector end (which is helpful since they're the easiest one to swap anyway, and the others you'd need a proper tool for).

 

[maniac]

this is what I came up with...

 

[wrenaudrey]

I've found this post/article when i was searching around for a DIY guide to make a cheap voltage fan switch.

http://www.silentpcreview.com/forums/viewtopic.php?t=22943

No idea if its correct but it says...
"The 7 Volt Mod
Good: 7 volts is a good compromise between noise and airflow for most fans.
Bad: It could kill your power supply (read blue caution box).
A little explanation on the PSU problem, since this is a common question. Essentially, when you create the 7 volt molex plug, you're taking current and feeding it back into the PSU. Normally, current only goes out the 12 V and 5 V lines of the PSU. To create the 7 V plug, you're taking current out the 12 V line, and putting it in the 5 V line. In theory, if the current is low enough, the PSU will be able to handle it. Just be aware that the PSU was not designed to do this, and there is anecdotal evidence that it can kill a PSU."

 

[maniac]

I've found this post/article when i was searching around for a DIY guide to make a cheap voltage fan switch.

http://www.silentpcreview.com/forums/viewtopic.php?t=22943

No idea if its correct but it says...
"The 7 Volt Mod
Good: 7 volts is a good compromise between noise and airflow for most fans.
Bad: It could kill your power supply (read blue caution box).
A little explanation on the PSU problem, since this is a common question. Essentially, when you create the 7 volt molex plug, you're taking current and feeding it back into the PSU. Normally, current only goes out the 12 V and 5 V lines of the PSU. To create the 7 V plug, you're taking current out the 12 V line, and putting it in the 5 V line. In theory, if the current is low enough, the PSU will be able to handle it. Just be aware that the PSU was not designed to do this, and there is anecdotal evidence that it can kill a PSU."

Dammit, now I'm abandoning this idea, I've already ruined two power-supply's, true they were crap but still. I am scared of ruining it, I guess I'll just live with it. Thanks for your help anyway.

 

[jamesriley94]

Dammit, now I'm abandoning this idea, I've already ruined two power-supply's, true they were crap but still. I am scared of ruining it, I guess I'll just live with it. Thanks for your help anyway.

It's never going to kill your PSU, don't worry.

A couple of PSUs occasionally get confused and turn on, then off, then back on again - and after that they're fine.

Bitfenix sell 7v molex to fan splitters, and if there was any danger of one of those destroying a PSU, I'm sure they wouldn't be selling them.

 

[mehere]

It's never going to kill your PSU, don't worry.

A couple of PSUs occasionally get confused and turn on, then off, then back on again - and after that they're fine.

Bitfenix sell 7v molex to fan splitters, and if there was any danger of one of those destroying a PSU, I'm sure they wouldn't be selling them.

having just bought 15 of these fans I got one or two of those splitters laying about and have never had a problem running 7v even on a 18w pump

 

[SuB]

I know this might sound daft, but don't Sata power connectors provide 7v.. using 5v wires and 12v wires and a lot of those come from a 4pin connector these days at the PSU end..

How do you think they manage that?

I'm sure I remember something about them having a 7v source in there by crossing 5v and 12v ?

edit: Looking this up I could be mis-informed.

I still doubt this would break anything we've been doing it for donkeys years...

 

[mehere]

I know this might sound daft, but don't Sata power connectors provide 7v.. using 5v wires and 12v wires and a lot of those come from a 4pin connector these days at the PSU end..

How do you think they manage that?

I'm sure I remember something about them having a 7v source in there by crossing 5v and 12v ?

edit: Looking this up I could be mis-informed.

I still doubt this would break anything we've been doing it for donkeys years...

dont you hate it when people take the myth

 

[SuB]

hmm.. *shrug* I was sure there was something about 7v using sata.. I must look that up when I have time.

 

[wrenaudrey]

I didnt intend to tell you not to make/use 7v modded molex's.
Just thought i'd link something that i read somewhere hoping someone could elaborarte, share their experience or prove that it really do kill PSUs.

But based on the reply, im guessing the damage is so minimal or it doesnt happen at all.

 

[Remmy]

Is it out of the question to simply use resistors or something?

 

[maniac]

Is it out of the question to simply use resistors or something?

nope not out of the question, but I'll probably just use the extension I created and if something fucks up I'll blame all of you haha no really, I will!

 

[Remmy]

nope not out of the question, but I'll probably just use the extension I created and if something fucks up I'll blame all of you haha no really, I will!

Haha, I have like 13 of the Corsair 12v->7v inline resistors that I'd just give you but sending them to Malta is probably too far lol. Then again, they are very small, do you want some?

 

[mehere]

Is it out of the question to simply use resistors or something?

its not out the question but there is a lot of maths involved and the speed will vary fan to fan type as each fan will have a different current draw and if you wish to reduce a group of fans together on one resister it will produce heat in its own right

 

[Lyndon]

You can use resistors pretty easily, just work out the voltage you need it to be (7v) the source voltage (12v) and the current draw of the unit you want to run, that'll give you the rating you need and also the wattage of the resistor if it's quite high power.

Here's an online calculator http://led.linear1.org/1led.wiz

The current for the fan should be on the sticker on the centre usually I think

 

[mehere]

You can use resistors pretty easily, just work out the voltage you need it to be (7v) the source voltage (12v) and the current draw of the unit you want to run, that'll give you the rating you need and also the wattage of the resistor if it's quite high power.

Here's an online calculator http://led.linear1.org/1led.wiz

The current for the fan should be on the sticker on the centre usually I think

I didn't say its out of the question and the maths are not that simple as the current draw drops with voltage drop hence fans rarely state current just the power rating at 12v
so given the power and the voltage you can work out the current
but you also need to know the resistance of the fan
knowing this you need to work out the current at the running voltage you want
this current will be the same through the resister as the fan
12v minus the running voltage is the voltage drop across the resister
knowing the voltage across the resister and the current through it you can work out the resisters value and the min power rating of it
and how many of us here will go through all that?
we just run them on 5/7v or get a fan controller
the link is for leds not that good for fans