Increasing fan speed

[ervand]

Hello,
Number one thing you should know is that I never worked with electricity and wires, so I need your help! If you could try to explain with simple words it would be great because I am not familiar with terminology.

What I have:
- I have two 120mm fans. First fan works great and moves a lot of air. Second fan should be pretty much the same as the first fan, but for some reason it doesn't move as much air. I've found a tutorial that explains how to change voltage, but it wasn't clear enough for a noob like me.

What I am trying to achieve:
- I want to make it spin faster. I don't care about the noise. My goal is to have two fans mounted on each other. the black fan (the one that moves less air) will be in front and will be painted into metallic color with some more additions to it to make it look like a turbine. and then there is another fan behind it (the one that moves a lot of air) that is made of clear plastic and has blue leds. It is going to look cool, but I also want it to move air. When I put this fans together one behind is moving a lot of air, and one in front moves not as much, together it comes up with almost no air moving outside of the case......... My guess is that if I make both fans move same amount of air it is going to work......

PLEASE HELP ME WITH IT, because now this little problem is a stopping point to my big project.

I took some pictures, so that you can figure out what my current set up for the fan that move less air is:

http://img264.imageshack.us/img264/1218/sn201464smallmi0.jpg

http://img443.imageshack.us/img443/2999/sn201473smallmh3.jpg

http://img337.imageshack.us/img337/4663/sn201470smallqv2.jpg

http://img443.imageshack.us/img443/9869/sn201472smallav2.jpg

PS: I have technical information of both fans if needed:

Clear fan (that moves a lot of air):

Fan Dimension: 120 x 120 x 25mm
Noise Level: 22 dB(A)
Airflow: 42.31CFM
Input Voltage: 11.2~12.2VDC
Output Current: 5~7.5mA
Output Frequency: 40kHz+-20%
Rotation Speed: 2800~3200RPM
Bearing Type: sleeve
Black fan (that moves less air):

Fan Dimensions: 120 x 120 x 25mm
Noise Level: 28 dB(A)
Airflow: 47 CFM

[Mach]

I'll have to find the link but IIRC, the physics of this will actually result in less air moved. Hmmm, hang on.

Yup - http://www.silentpcreview.com/forums/viewtopic.php?t=25952&highlight=fan+stacking
http://www.modders-inc.com/modules.php?name=Forums&file=viewtopic&t=1332&highlight=fan+stacking

If you read the threads, it was suggested that you can reverse the fan with better results. Seem counter-intuitive but give it a shot.

As far as overvolting a fan, I'd say bad idea using your main PSU. This thread suggests that you can try a Pico psu (http://www.logicsupply.com/categories/power_supplies/power_supplies) as a alternate psu.

http://www.overclock.net/cooling-experiments/283214-overvolting-fans.html

xmastree (or a resident EE) may be able to offer better guidance on the overvolting and the potential for expensive magic blue smoke release.

[ervand]

I didn't know overvolting a fan is dangerous for my psu. I guess I am not going that direction...

In those topics guys talk about efficient cooling...... I don't care about the cooling efficiency. I just want to make my front fan move at least some amount of air, so that it at least some purpose to it other then the visual image =)

[ervand]

Anybody else? =/ Anything else? =/
I still can't get decent air flow of you these things.

[J-Roc]

Let me hit you with some knowledge! (i've been waiting to use that for a while :) )

when you stack fans directly on top of each other you dimish performance because of the turbulance created between the small gap of the fan blades. This could be solved by glueing or attaching the blades so they move in unison. This wont work for computer fans because of the motor bracing. The other way is to create a tunnel with stationary fins which channel the air down the tunnel.

In this photo you can see a baffle which seperates the air column. You need to make somthing like that between the fans so the air stops rotating and starts to move straight towards the second fan.
http://www.commercemarketplace.com/home/CollectAir/blctunnel.jpg

I would recomend a honeycomb high profile mesh in between the fans. Allthough i am no expert in areodynamics...

[xmastree]

http://www.overclock.net/cooling-experiments/283214-overvolting-fans.html

xmastree (or a resident EE) may be able to offer better guidance on the overvolting and the potential for expensive magic blue smoke release.

http://bestsmileys.com/blushing/3.gifHow could I refuse?

Right, I've never tried this but I looked at Mach's links and found this (http://www.overclockers.com/tips808/) which makes perfect sense (apart from the dodgy English). It had actually crossed my mind before I read it, but that page confirms the idea.

Basically, if you connect the fan between either +12 and -5 or -12 and +5, you'll get 17 Volts across it, making it run faster.

To really burn it up go from +12 to -12 and get 24V, but this might over do it slightly.

I'd test the fan on a spare PSU first, if you have one available.

J-roc is right about the baffles too. You need to stop the air spinning as it exits the first fan. This makes it difficult to mount the fans close together as you won't have room for any baffles between them.