up the airflow with two fans in series?

**scott_fx** · 06-08-2005, 03:39 AM

i was just wondering if you guys have ever tried to put two fans on top of each other? would this increase airflow since there would be twice as much blade surface? I have limited space and can only mount one 80 mm fan but i there is enough clearance to stack one on top of another.

thanks in advance

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**Tidder** · 06-08-2005, 03:42 AM

Instead of doing that, why not hook your fan up to the +12v on the positive side, and the -5v instead of ground on the negative side? This would give you 17 volts to the fan instead of 12, which would increase air flow as well.

**scott_fx** · 06-08-2005, 04:04 AM

i didn't even know that was possible.
it posses a few questions though, maybe you could shed some more light on the subject:
1: will the longevity of the fan be greatly compromised running at that voltage?
2: how much louder would it be? would it be louder then two fans piggy-backed?
3: would it flow more then the two fans?

**Tidder** · 06-08-2005, 04:15 AM

I would guess that the longevity would be shortened, but by how much, I'm not sure. I'll have to set up a PSU and fan, and just let it go 24/7 and see what happens.

I would guess that it would flow more air than the 2 fans together. I would think that putting 2 fans together would not do all that much better than one fan. Reason being that the second fan doesn't have much room to grab more air, you're still going to be pushing the same amount of air that the first fan could grab.

It would definitely not be as loud as 2 fans together. 2 fans piggy-backed creates some aweful noise.

You can get 24 volts out of a PC PSU. There are -5v and -12v lines. So really you could even put 24 to your fan, but that's really not recommended. I've actually used the opposite to help keep my fans more quiet. Hooked the ground to the PSU +5v and the positive to the +12v to create a 7v connection. Keeps it cool and a little more quiet. I'll set up a PSU with a new fan and see what happens pushing 17v to it.

**RS3RS** · 06-08-2005, 04:17 AM

I've heard stories of fans being piggybacked dying sooner, because of the extra resistance they have to force their way through. And I don't think they'd move that much more air than one fan anyway... I also don't think I'd trust a fan running at 17 volts either...

To be honest, it seems like the best solution here is to either:
1.) Add more holes for fans,
2.) Put in BIGGER fans (ie, 120's)
3.) Buy a Vantec Tornado/Delta and put up with the noise

Of course, if the fan isn't mission critical, I don't think you could hurt too much stuff by playing with voltages/piggybacking. I personally wouldn't play with voltages too much though, just for the sake of my poor PSU.

**Tidder** · 06-08-2005, 04:27 AM

PSU won't suffer from upping the voltage to your fan. You fan only pulls like .25 amp, power supply doesn't care.

**scott_fx** · 06-08-2005, 04:28 AM

thanks guys for the quick and usefull feedback... i think another option for me is to just put two more fans in the 'channels' to help pull more air and from the intake fan.

maybe this pic will shed some light on what i am thinking:

i could mount the fans about 1/4 away from the ends but hidden under the carpeted piece. the amp and pc may not even need the extra air flow but i had a few extra fans left over and was thinking about putting them to good use.

**Tidder** · 06-08-2005, 04:32 AM

Yeah, just use the extra fans if you really need the air, I wouldn't mess with voltages if you have room for extra fans.

**RS3RS** · 06-08-2005, 04:42 AM

Originally Posted by Tidder

PSU won't suffer from upping the voltage to your fan. You fan only pulls like .25 amp, power supply doesn't care.

Yeah, just by the drawing extra current I couldn't see anything happening. I have, however, heard stories from guys over at the [H] blowing up lower-quality power supplies by using one of the positive lines as a ground (Ie, 12v+ to the fan's + lead and 5v+ to the fan's - lead). Of course, that could just be some sort of a coincidence though.