Strange fan wiring idea?

frosty · Post by **frosty** » Thu Oct 07, 2004 12:17 pm

Hey got this idea while counting the ceiling tiles last night.

If I wire a jumper from one molex connector on the 12v side or gold wire and then jumper it to another molex to the red or 5v side and then connect two fans in series
would they both be running at 8.5 volts or would I just burn out my coveted PSU?

Also what about wiring two molex red wires or 5v together to one fan to get 10 volts?

sthayashi · Post by **sthayashi** » Thu Oct 07, 2004 12:23 pm

That's never going to happen. If you jumper a yellow and a red, you probably will hurt something (at best, your PSU will do short circuit prevention and just shut off).

But you can't add voltages like that. Wiring two red wires together will get you a total of 5v, not 10 volts. Jumpering 2 reds won't do anything.

Post by **Rusty075** » Thu Oct 07, 2004 12:42 pm

I think you've lost me....

What you could do is attach the positive lead of the fan to the 12v of the molex, and the negative to the 5v, to run the fan at 7v. (aka, "The 7 volt Trick") You could wire two fans in parallel that way and have them both at 7v, or in series and have them both at 3.5v (if they'll start)

Is that what you were thinking?

frosty · Post by **frosty** » Thu Oct 07, 2004 1:11 pm

I understand the 7 volt wiring Rusty, but am afraid to go longterm and hurt the coveted PSU, I had this crazy idea that if you combine two separate molex's using one red and one gold wire youd get 17 volts

Then split the 17volts by wiring two fan in series thus = 8.5.

I love how you can post retarded stuff here and you guys remain so kind and polite.

I am going back to counting tiles now, 56, 57, 58...........

sthayashi · Post by **sthayashi** » Thu Oct 07, 2004 1:29 pm

They're still connected to each other INSIDE the PSU. In fact, I would wager that's a safe assumption.

Sorry, but there's no way to add voltages like that. The only way I can think of MAYBE doing that is to use another/different power supply and cross voltages that way.

Post by **Rusty075** » Thu Oct 07, 2004 1:39 pm

sthayashi wrote:They're still connected to each other INSIDE the PSU.

....unless the PSU truly has separate 12v lines.... (I think) But that wouldn't help with the 5v line, obviously.

sthayashi · Post by **sthayashi** » Thu Oct 07, 2004 1:56 pm

Rusty075 wrote:
sthayashi wrote:They're still connected to each other INSIDE the PSU.
....unless the PSU truly has separate 12v lines.... (I think) But that wouldn't help with the 5v line, obviously.

The grounds (i.e. reference) line will still likely be the same though. To NOT assume that can be very dangerous.

mathias · Post by **mathias** » Thu Oct 07, 2004 7:45 pm

I though about this kind of stuff quite a bit also. Here's how I understand it.

You cannot add together the +12 and +5 lines. If you were to attach both those lines to the +12 fan wire, power would go straight between the +12 and +5 lines.

However, you could do this with the +12 line as the +12 line, and the -5 line as the ground. That would give you 17v, 8.5 with two electricaly identical fans.

But why bother with the paired fans, you could instead use the +5 and -5 lines, or the +3.3 and -5 lines, easy 8.3 volts with no wrong way current.

The problem is, -5 (and -12) power lines only go to the motherboard, so you would have to get a MB power cable extender(or just cut the power supply wires).

sthayashi · Post by **sthayashi** » Thu Oct 07, 2004 7:53 pm

mathias wrote:The problem is, -5 (and -12) power lines only go to the motherboard, so you would have to get a MB power cable extender(or just cut the power supply wires).

Even worse, more and more power supplies don't even bother supplying -5V. It's been removed from the specs since ATX v1.3

mathias · Post by **mathias** » Thu Oct 07, 2004 8:22 pm

sthayashi wrote:
mathias wrote:The problem is, -5 (and -12) power lines only go to the motherboard, so you would have to get a MB power cable extender(or just cut the power supply wires).
Even worse, more and more power supplies don't even bother supplying -5V. It's been removed from the specs since ATX v1.3

Damn. I wish they got rid of the -12 line instead. If it was deemed unnecessary, they should just do a simple refit on older designs and include 10v and 8.3v fan sockets, Zalman units do already include 5v adaptors.

The -17v trick should still be possible with the -12 and +5 lines.

sthayashi · Post by **sthayashi** » Thu Oct 07, 2004 8:53 pm

mathias wrote:The -17v trick should still be possible with the -12 and +5 lines.

Actually, it'll still be the 17v trick (no negatives needed). It's just that you're dumping current onto the -12v line, which probably isn't healthy, but probably isn't much more unhealthy than the 7v mod.

mathias · Post by **mathias** » Fri Oct 08, 2004 7:09 am

sthayashi wrote:
mathias wrote:The -17v trick should still be possible with the -12 and +5 lines.
Actually, it'll still be the 17v trick (no negatives needed). It's just that you're dumping current onto the -12v line, which probably isn't healthy, but probably isn't much more unhealthy than the 7v mod.

The - must have been a typo.

Why would this be unhealhty? With the 7v trick, due to being paired with a line 7v higher instead of 5v lower, the 5v line would be acting as a minus line instead of a plus line. But, assuming the -12 line is normally paired with the ground, if it was paired with the +5 line, it would still act as a minus line like it normaly does. The only danger I see is if the limited amperage of a minus line is exceded.

burcakb · Post by **burcakb** » Fri Oct 08, 2004 8:06 am

If you really want to go adventuring, how about this?:

Your PSU has free power lines that you can use: two 3.3V lines and one 5V line. Where? on that 6pin thingy (the AUX connector) that your regular mobo doesn't use. I've already cannibalized that socket to get me low-voltage molex sockets to undervolt my 120mm fans.

Now you could improvise a connection of the above mod with the 7V trick. Instead of running the regular 5V line as the ground, you could run the 3.3V line as the ground to give you 8.7V line. You'll have to change the metal pins on the AUX socket to go into a molex but then, hey, nothing is free

sthayashi · Post by **sthayashi** » Fri Oct 08, 2004 8:31 am

burcakb wrote:Now you could improvise a connection of the above mod with the 7V trick. Instead of running the regular 5V line as the ground, you could run the 3.3V line as the ground to give you 8.7V line. You'll have to change the metal pins on the AUX socket to go into a molex but then, hey, nothing is free

Just as innovative would be to take advantage of built in SATA connectors. They're supposed to provide 3.3V

Mathias, I'm not as familiar with negative voltage, so you're probably right.

frosty · Post by **frosty** » Fri Oct 08, 2004 11:09 am

[quote="burcakb"]If you really want to go adventuring, how about this?:

Your PSU has free power lines that you can use: two 3.3V lines and one 5V line. Where? on that 6pin thingy (the AUX connector) that your regular mobo doesn't use. I've already cannibalized that socket to get me low-voltage molex sockets to undervolt my 120mm fans.

That is intriqueing Bur, the 6 in tingy is the one that does not go on the mobo, well the 3.3 lines are they a specific colour then?

Thanks for the injection of blood in this string, I find it pretty fascinating.
/edit Geek mod huh?

sthayashi · Post by **sthayashi** » Fri Oct 08, 2004 12:02 pm

frosty wrote:That is intriqueing Bur, the 6 in tingy is the one that does not go on the mobo, well the 3.3 lines are they a specific colour then?

Orange

frosty · Post by **frosty** » Fri Oct 08, 2004 12:59 pm

Thnaks sth, now I gotta decide which fan I want at 8.7 and which at 5 and so on and so on.

The silent bug has bite me!!!

MagnusT · Post by **MagnusT** » Fri Oct 08, 2004 6:20 pm

Some interesting reading on what was mentioned earlier, that the 12V on different molex cable harnesses coming out from the PSU are still connected inside the PSU. As was mentioned before the answer is "yes.... and a sort of no". But the ideas initially suggested of course will not work due to the common reference ground. An interesting read: http://hardforum.com/showthread.php?t=779582

It's really confusing with all the different ATX and ATX12V revisions overlappping each other, not to mention getting into the EPS12V standards

Then over to this brilliant idea!

burcakb wrote:If you really want to go adventuring, how about this?:

Your PSU has free power lines that you can use: two 3.3V lines and one 5V line. Where? on that 6pin thingy (the AUX connector) that your regular mobo doesn't use. I've already cannibalized that socket to get me low-voltage molex sockets to undervolt my 120mm fans.

Now you could improvise a connection of the above mod with the 7V trick. Instead of running the regular 5V line as the ground, you could run the 3.3V line as the ground to give you 8.7V line. You'll have to change the metal pins on the AUX socket to go into a molex but then, hey, nothing is free

Here are some pin out pictures:

The ATX12V extra 4 pin 12V connector (also known as the P4)

Additional pinout pictures:
http://www.hardwarebook.net/connector/power/atx12v.html ATX12V (P4)
http://www.hardwarebook.net/connector/power/atxaux.html ATX12V 6 pin with 3,3 and 5V
http://www.hardwarebook.net/connector/p ... ional.html The odd ATX12V 6 pin with fan sense and stuff

I'm not sure how the new PCI Express 6 pin connector is configured though....

MagnusT · Post by **MagnusT** » Sun Oct 10, 2004 12:55 pm

MagnusT wrote: Additional pinout pictures:
http://www.hardwarebook.net/connector/power/atx12v.html ATX12V (P4)
http://www.hardwarebook.net/connector/power/atxaux.html ATX12V 6 pin with 3,3 and 5V
http://www.hardwarebook.net/connector/p ... ional.html The odd ATX12V 6 pin with fan sense and stuff

Well, just out of curiousity I spent some time trying to understand all the different and overlapping ATX and ATX12V specifications.

http://www.hardwarebook.net/connector/power/atxaux.html
This one is not correct. There is no such 2x3 row connector with these voltages. The voltages, pins and connector part number is the good old 6 pin single row "Auxiliary Power Connector" . The drawing of a 2x3 connector is wrong.

http://www.hardwarebook.net/connector/p ... ional.html
This one is the new "Optional Power Connector" that was introduced quite recently in the specifications but I doubt it has hit the streets anywhere at all yet...

MagnusT wrote: I'm not sure how the new PCI Express 6 pin connector is configured though....

Well I did find out and made this page with all listed: http://tystpc.nu/sida.php?s=psu

MagnusT · Post by **MagnusT** » Sun Oct 10, 2004 12:58 pm

Oh, and BTW. The new "Optional Power Connector" is supposed to have a fully floating ground for the 1394 power!! So some "impossibles" just might be possible anyway

silvervarg · Post by **silvervarg** » Mon Oct 11, 2004 12:05 am

Frosty:
I understand the 7 volt wiring Rusty, but am afraid to go longterm and hurt the coveted PSU

The 7Volt mod is using +12 as positive line and +5V as GND. This could is theory be bad for the PSU, but since you draw a lot more power from the +5V the net will be that no current will be dumped into the PSU +5V.

Doing the same thing with the +12volt as positive and the +3.3V as GND will be just as bad for the PSU as the 7V mod. Assuming that you draw considerably less current from the +3.3V line (mostly RAM usues this on new boards), so this should be a worse option than the 7volt mod IMHO.

How about just wireing two identical fans in series with each other?
This is the classic 6volt mod, and there is no way that this could be bad for the PSU.
The positive thing with this change is that if one fan shorts out the other fan will go to 12V automatically, so CFM with be almost unaffected if this happens.
The negative thing is that if one fan breaks down it could cut power to both fans. This is the only negative thing I can see with the 6Volt mod.
Almost all fans start reliably at 6V, but lots of fans have problems to start reliably at 5V.

As for keeping the -12V line I do believe that it is much more usefull than the -5V line. Lowering DC voltage is much easier than raising DC voltage, so higher voltage is more flexible.
Sound circuitry typically use both positive and negative voltage, so the -12V line is probably used in your computer, but that -5V line is probably not used even if you still have that line.

frosty · Post by **frosty** » Mon Oct 11, 2004 7:11 am

Thx for the input, I think the 6 v idea is fab. - I have had problems with getting even good 80 L panaflos to start at 5 v because I think so much fine dust accumulated in my system in such a short time. I noticed after cleaning the fans and replacing my filter in the front of the case the fans are starting fine at 5 v, one over the cpu and one over th vid card and the exhaust fan on a fanmate.

I finally grew some BALLS and decided to live with higher temps and so pleased with a almost noiseless system, she did not even know it was on this time and tried to boot it up. When you fool a women's hearing you got something special. hehe : )