Rewiring the laptop fan to usb via mini pcie to to make it run 100%

Dear all,

I have a sager np8662 with qx9300 OC from 3.19ghz to 3.72 Ghz. With my use (3d architectural rendering and modeling) this laptop gets really hot especially when im mobile without the laptop cooler. I researched about my 3-wire laptop fan and discovered the 3 wires are positive(red), ground (black) and tachometer (yellow). The built-in fan of np8662 can get very powerful, but it only spins 100% when it gets to about 85-90 degrees C which makes the laptop hot to the touch and worrisome. I live in the Manila and it's summer here so ambient temps indoors get to about 38 degrees also. I don't mind if the laptop gets too noisy because i am more concerned with the temps. Now here's the thing:

I have a vacant mini pcie port where i can attach a mini pci to usb hub. I'll take the 5v 500ma power supply from the usb hub and connect it to positive and ground connections on the fan to bypass fan speed control from the motherboard but i will leave the tachometer wire connected to the motherboard. I tried using an external 5v power supply to power the fan and it runs beautifully at 100%. I tried doing this while with the fan placed on the laptop but it beeps and then shuts down presumably because it could not detect the tachometer.

here are my questions:

would it be safe to reroute the power source to usb? (technically the fan works fine with a constant 5v 500ma power supply) while keeping the tachometer connected to the motherboard? i don't understand the wiring diagram attached very well and i am wondering if doing this would damage the connection linked to the tachometer if the power source came from somewhere other than the laptop fan power source.

 

Leaving the fan speed cable still attached will negate rerouting the power - 5V is fed constantly to the fan, it's the third cable that changes the speed by adjusting the voltage. I used to draw power from the fan connector, and 5V on red was there constantly while fan was running, but yellow cable changed voltage from lower to higher (1.0V to 5.0V) as fan speed increased.

I *think* that you can run it at 100% all the time by feeding 5V to both the red and yellow cables, but I'm not sure, you'll need to test that. Drawing from USB should have no effect on anything (since it's a fan, it uses little power).

If 5V on red+yellow works for 100% fan speed, you could separate the yellow cable using two diodes (just in case) and feed it 5V from the red cable, no need for miniPCIe card...

 

I know for my N61Jq laptop, if you cut one of the three wires (don't remember the color), it will result in the fan spinning at 100% constantly.

Not sure if the same would apply to your laptop.

 

Hi Jotm,

I will try that, i have another 3wire laptop fan although it's from an HP. but presumably it works similarly because it's also from the same manufacturer. i tried running the fun with the yellow cable removed, but the laptop kept on beeping. i'll post an update when i have to test.

 

Hi Loney111111,

i'll give that a try as well, but removing the yellow wire didn't work. thanks

 

I'm attaching a diagram of the fan wiring in the laptop which i got from the service manual, but i don't understand any of this, if there's someone out there who understands these diagrams and can interpret a solution based on my problem above i would be very grateful. thanks

 

Does the laptop beep when the fan is completely disconnected? The diagram shows that the yellow cable is attached to a fan sensor, don't know how it works though...

 

Hi Jotm,

yes it beeps and shuts down after about a minute, i just remember before when i still had and hp, i had the gpu reflowed and repaired because of heat issues and the technician rewired my laptop fan to a different power source, just one wire but i could not remeber which it was. it was a smaller 3-wire fan and he was able to make it run constantly. I should try to visit a laptop repair specialist to see if that will will work with this sager.

 

try giving the ground from another source , my touching the screw or something . This should override the laptop fan control

 

That's the problem - your laptop has a sensor and won't run if the fan is not detected. HPs (and other laptops) run without the fan, there's no sensor at all. It's a good thing since it guarantees it won't overheat, but in your case it makes it hard to get the fan to spin at 100% all the time. Also, from my observations, the difference between 5200 RPM and 4200 RPM is minimal - you'll drop 1-2 degrees at most (but maybe it's different in your case)...

 

Just an update, i had the fan rewired by a laptop technician and now my main fan runs 100% all the time. It's actually quite simple, he just diverted one of the cable to another power source. Will post the photos when i have extra time.

 

Cool. Please post those pictures.