Running fans from a wall plug

wussboy · Post by **wussboy** » Tue Feb 10, 2004 10:01 am

I know there has been some talk about this earlier, but I'd like to nail down specifics. I'd like to run as many as 4x120mm fans at 7-12v off of a wall converter (they blow on my water rads which are nowhere near my computer). Can this be done? As long as the converter is 12v, I know I can run 1 fan, but what happens if I run several fans? And which wires need to get attached to which wires? I'm completely okay with stripping wires and twisting them together. Help appreciated! Thanks.

zuperdee · Post by **zuperdee** » Tue Feb 10, 2004 10:14 am

Running 4 DC-powered fans from a wall transformer ought to work, so long as your wall transformer is rated to provide enough amperage. I'd suggest that you start by adding up how many amps the 4 fans require, then multiplying that by 2, in order to make sure you have enough headroom for the peak draw of the fans, as well as for a safety factor.

As to which wires to connect: generally, red will be the positive wire, black the negative wire, and yellow the tach wire, which you can connect to the tach signal of a fan port on your motherboard, if you are really ambitious.

To run the 4 fans from the wall transformer in parallel, all you have to do is twist all the reds and all the blacks together, then hook them up to the transformer.

Good luck to you--but one question first: Why can't you run them from your computer's power supply?

zuperdee · Post by **zuperdee** » Tue Feb 10, 2004 10:18 am

A couple clarifications/corrections to what I said earlier: I just realized you did say these fans won't be anywhere near your computer.

I assume that's why the need for a wall transformer.

And as to the wires: When I said twist them together, what I meant was: twist all the reds together and hook them up to the positive side of the transformer, then twist all the blacks together and hook them up to the negative side. Obviously, you don't just want to twist the reds AND blacks together into one big lump. hehe.

lenny · Post by **lenny** » Tue Feb 10, 2004 10:33 am

wussboy wrote:I'd like to run as many as 4x120mm fans at 7-12v off of a wall converter.

As long as your wall converter has enough juice. Time for ASCII graphics again...

Code: Select all

Wall plug (+)---R---x----x----x----x
                |   |    |    |    |
                |  Fan  Fan  Fan  Fan
                |   |    |    |    |
          (-)---x---x----x----x----x

R (optional) is a regulator circuit that allows you to switch voltage if you need the feature. Or it can be as simple as a switch that switches between a short circuit and a resistor.

Essentially, if the fans are wired in parallel each will receive the full voltage. And total amps drawn is the sum of the amps drawn by each fan (ditto for power).

Hopefully this doesn't come across as too simple.

By the way, there are AC 120mm fans available too.

zuperdee · Post by **zuperdee** » Tue Feb 10, 2004 10:48 am

lenny wrote:By the way, there are AC 120mm fans available too.

True--I know Sunon makes some, but it seems to me AC fans are usually rated to be not as quiet as DC brushless ones, for some reason. (Anyone know why?)

zuperdee · Post by **zuperdee** » Tue Feb 10, 2004 10:49 am

Of course, actually, since the original post did say these fans will be nowhere near the computer, I assume it might even be possible these fans could be put in a closet or something, so maybe the noise difference doesn't even matter, and AC fans would be better for simplicity and robustness...

wussboy · Post by **wussboy** » Tue Feb 10, 2004 4:40 pm

Putting them in the closet is precisely the idea. Lenny, is your graph basically what zuperdee said? It looks that way to me. I'll just lump all the reds and all the blacks together. Any idea on what the approx amperage draw is on a 120mm fan? Thanks again.

flyingsherpa · Post by **flyingsherpa** » Tue Feb 10, 2004 4:56 pm

amp draw is usually on round the fan label. sometimes it just says watts... so remember P = IV (power = current * voltage) so if it says 10 W, then current is 10W/12V = .83 amps assuming you're running at the full 12 V. but add up the amps for each fan.

wussboy · Post by **wussboy** » Tue Feb 10, 2004 11:19 pm

Thanks, flyingsherpa. I now feel confident I can find a suitable wall adapter. Thanks everyone.

zuperdee · Post by **zuperdee** » Tue Feb 10, 2004 11:34 pm

No problem. Let me know how it goes--this sounds like an interesting idea!!

wussboy · Post by **wussboy** » Thu Feb 12, 2004 1:39 pm

If I ever get my hands on a digital camera, I'll post some pics. But it will be a few months before I get everything together. I am moving at the end of April and I don't want to set everything up here just to have to take it down again.

Gooserider · Post by **Gooserider** » Fri Feb 20, 2004 3:45 pm

If you can't find a wall adapter with sufficient cojones to do what you want, a couple of alternatives might be

1. Use multiple adapters, each powering a small number of fans.

2. Purchase a cheap 110-12v transformer and a bridge rectifier and build your own

3. Try an automobile battery charger, some models can put out serious amperage...

Gooserider

wussboy · Post by **wussboy** » Sun May 23, 2004 2:39 pm

I have a few questions about fans and amps. The Panaflo 120mm M fan states a rated current of 340mA and a rated input of 4.08. Which number do I care about? I've found a great 500mA adapter that has 6v-12v options. Does the Amp draw stay the same even if the Voltage is lowered? Namely, at 12v it looks like I could only run one fan per adapter, but what about at 7v? Would the mA drop to ~250?

chylld · Post by **chylld** » Sun May 23, 2004 3:17 pm

well you can calculate the internal resistance of the fan as V/I = 12/0.34 = 35.3 ohms. if you feed the fan only 7v, then the current draw will be V/R = 7/35.3 = 0.198 amps, so in theory, yes you can run 2 fans off this provided you only give them 7v.

wussboy · Post by **wussboy** » Sun May 23, 2004 7:55 pm

Thanks, chylld. Man, am I ever glad smart people hang out here. Otherwise I'd be screwed!

So I hope by this weekend to have my little "project" done!

Just out of curiousity, what would happen if the fans were drawing too many amps? Would the fans burn? Spin slower? Would the power adapter burn?

Post by **Rusty075** » Sun May 23, 2004 8:06 pm

The power adaptor would likely fail, eventually. It may just run hot for weeks or months, if you're only slightly beyond its rating, but eventually it'll probably die a premature death.

I love the smell of melted plastic in the morning!

I speak from experience....I ran 10 92mm fans, with a total draw of 3amps off a 1amp power brick. Briefly

silvervarg · Post by **silvervarg** » Mon May 24, 2004 5:05 am

Usually there are 3 types of wall-mart adaptors:
AC, DC unregulated and DC regulated.

AC is not good to power fans from.
Both DC unregulated and DC regulated should do fine.

Most wall-marts adaptors does have a fuse in them, so if you just slightly overload them the fuse should burn out sooner or later.
If you short circuit the wall-mart adaptor you may be able to kill it.
At least any overloading will not harm your fans, and since they cost more than the wall-mart adaptors this is good news.

chylld · Post by **chylld** » Mon May 24, 2004 5:54 am

be careful with dc unregulated vs regulated. if in doubt, always buy a regulated ac adapter otherwise u could be in for a nasty surprise.

if you put some fans onto an unregulated ac adapter such that the fans don't draw near the designated amperage of the adapter, then the fans will actually be fed ~1.4 x nominal voltage. e.g. i'm running 2 papst 4412fgl's off a 9v 1a ac adapter, in parallel, and they each get over 12volts without a resistor in the loop. so be careful

wussboy · Post by **wussboy** » Tue May 25, 2004 1:51 pm

CRAP! Okay, I found a 1700mAmp converter with selectable voltage, and I was about to cut the tip off and wire up my fans, but I have NO idea how to tell which is positive and which is negative. Any way to tell short of getting a volt meter? If I hook it up backwards, will there be hell to pay?

zuperdee · Post by **zuperdee** » Tue May 25, 2004 2:20 pm

wussboy wrote:CRAP! Okay, I found a 1700mAmp converter with selectable voltage, and I was about to cut the tip off and wire up my fans, but I have NO idea how to tell which is positive and which is negative. Any way to tell short of getting a volt meter? If I hook it up backwards, will there be hell to pay?

A volt meter is probably the safest and best way. Failing that, look at the wires; oftentimes, the negative side has a white stripe along it. If you hook up the wires incorrectly, I doubt it will do anything too serious--you'll know if it is hooked up the wrong way if your fans won't turn. DC Brushless fans typically ONLY turn with the current source hooked up the right way. There MIGHT be exceptions, but I don't know of them personally. (Horror stories, anyone?

)

wussboy · Post by **wussboy** » Tue May 25, 2004 2:22 pm

I have some shit fans sitting around (thermaltake volcano 9 anyone?). I'll try it on them...and hope it burns them up!

chylld · Post by **chylld** » Tue May 25, 2004 10:32 pm

i've connected various fans the wrong way and nothing bad at all has happened to them. they even try to spin backwards a little

fancontrol · Post by **fancontrol** » Wed May 26, 2004 7:44 pm

when you're figuring out how much current you need, the label of the fan will say it all. keep in mind, though, that the numbers published are the absolute maximum power; reality will be 1/2 to 1/3 of that.

silvervarg, i believe the expression is "wall-wart" but maybe i'm too old to know that it has evolved into the name of a superstore.

finally, depending on your ambition, you can switch the power of the fans on/off from your pc without drawing much power from your computer. just two wires that would follow your water lines and a relay at the end. you could, in fact, switch a 'spare' ATX power supply in your closet on/off just to run your fans. the sick part is you can get a (crummy) PC power supply for about the same money as a wall-mart

and the ATX handles 10x the current.

Running fans from a wall plug

Running fans from a wall plug

Re: Running fans from a wall plug

Re: Running fans from a wall plug