Laptop fan juice

[Locum51]

Haha, had to come up with a creative title...

Back on track...i have two laptop fans from a HP Pavilion zd7000, i took the whole laptop apart ( I couldn't resist! ) and i want to make use of the fans; the problem is is that i can't seem to find the amount of volts they use.

I've searched everywhere and can't seem to find the voltage. I've found the whole cooling assembly but the specs aren't really listed. :facepalm:

I'll upload pics of the fans, if that helps.

[Oneslowz28]

Its either 3.3, 5 or 12v I can tell you that much! Its most likely 12v but could be 5.

[Spawn-Inc]

i would think it's 12v but as said above it could be 5v. so if you want to use them for something run 5v to them and either way your safe.

[Locum51]

Here's some pics....i'm thinkin' it's 5 volts but i uploaded some just to see if anyone knew exactly what voltage these use.

This is the speed controlled fan pin connector.
http://i108.photobucket.com/albums/n39/rsracing/101_0472.jpg
http://i108.photobucket.com/albums/n39/rsracing/101_0471.jpg

This is the bigger of the two fans.
http://i108.photobucket.com/albums/n39/rsracing/101_0469.jpg

Here is the smaller one...just a two pin connector.
http://i108.photobucket.com/albums/n39/rsracing/101_0468.jpg

[Locum51]

These fans are apart and ready for primer!
I'll post a little mod worklog! :]

[Locum51]

Sorry, no worklog...

If the fans ran 5V and say i used a normal 12V molex:
http://www.thebestcasescenario.com/forum/showthread.php?t=18428
^^^Would this work?

[Konrad]

Try spinning them up with 4.5V battery power? Most 12V fans I've seen don't do much with less than 7V. I could be wrong.

[FuzzyPlushroom]

Sorry, no worklog...

If the fans ran 5V and say i used a normal 12V molex:
http://www.thebestcasescenario.com/forum/showthread.php?t=18428
^^^Would this work?

They're probably 5v - most laptop fans I've seen are. I'd follow Konrad's suggestion of spinnin' 'em up off three batteries (AAA/AA/C/D) in series and seeing whether they come on, or just stick two pieces of wire into the 5v and ground pins of a spare Molex connector.

Regardless of voltage, I'd just cannibalise a fan passthrough from a junk case fan, if you have one, and switch the wires if you don't need to use the passthrough for anything else.

That diagram would work (note that the top "12v" wire will pass either 5v or 12v depending on the switch's position) but many 12v fans won't spin up from 5v, and putting 12v through a 5v fan will wear it out rather prematurely, so it'd seem pointless to wire such a switch up for these little guys. If they are 12v, the 12v-to-7v switch would be potentially useful, however. I hope all of that made sense.

[Konrad]

You can always plug a 5V fan into 12V power and just use an in-line resistor to reduce the voltage received at the fan:

so, using Ohm's Law, R (Ohms) = [12V-5V] / I(fan)
5V @ 0.10A = 70 Ohms (nearest E24 value is 68 or 75 Ohms, ±5%)
5V @ 0.15A = 46.67 Ohms (nearest E24 value is 47 Ohms, ±5%)
5V @ 0.20A = 25 Ohms (nearest E24 value is 24 Ohms, ±5%)

Lower value resistors will pull more voltage away from the fan, slowing it down. Higher values will pull less voltage away from the fan, speeding it up. There are limits, the fan won't spin below a minimum voltage threshold (maybe 2.5 or 3V) and won't last very long if pushed beyond it's rated spec (maybe 6V max). High precision isn't necessary, particularly since most fans will vary rpm by ±10% with normal voltage anyhow.

Bear in mind that this is essentially still the same circuit as a 12V fan, except that now the fan draws 5V and the resistor draws the other 7V; this isn't very efficient (it will drain your laptop battery a bit faster) as the power drawn by the resistor is only wasted (turned into heat, actually, which might be counterproductive). It's not a lot of power, but worth noting. Installing a 5V fan would be preferable, but I do know of a few people who've used 12Vs on their laptops and it caused them no problems.

The resistor should be rated 1W or larger (if it's too small it will eventually burn out) and it will get a little warm, so it won't hurt to place it away from heat-sensitive components if you can. 1W SMT resistors aren't common or necessary. Normal resistors are cheap, if you pay 10 cents for one then you've been robbed.

The resistor goes on the red wire.

An excellent way to implement this is shown here
http://www.pcshoptalk.com/staff/stefan_m/noctuap14flx/4.jpg
These are accessories that come with the Noctua NF-P14 FLX fan. The items of interest are the second and third from the left; the "Low Noise" and "Ultra Low Noise" adapters for the fan. They are simply 3-pin fan extension cables with different coloured connectors so you can tell them apart. You plug the fan into the noise adapter then plug the noise adapter into the mobo. If you look closely, you'll see how they work: the red wire uses a (neatly shrink-wrapped) small resistor as part of its length. The different values of these resistors are what makes the fan spin slower and quieter when they are installed.

You can always use a variable resistor (potentiometer) in place of the fixed-value resistor; the potentiometer is basically a little knob that can be turned to manually adjust the resistance (fan speed) during operation. This is the simplest form of a single fanbus (although not an efficient one).