Hi,
I have a laptop with a fan that has 3 speed levels. The speed level that the fan runs at is dependant entirely on the temperature of the CPU. When I turn the computer on the fan is completely off. As the temperature of the CPU rises, the 1st speed level kicks in. At this speed the fan is barely audible. If the computer is placed under load, the CPU temperature continues to rise and the 2nd and then eventually the 3rd speed level initiate. Both of these speed levels are loud and annoying.
I have confirmed that the CPU will operate below the maximum temperature threshold under full load for a long period of time on just the 1st fan speed level. Therefore my goal is to modify the fan such that it is off by default and then spins up to the 1st speed level when the CPU begins to heat up under full load. I do not ever want the fan to initiate the 2nd or 3rd speed level.
I have done some research into accomplishing this goal, but my lack of knowledge of electronics is hindering my progress. Here's what I know so far:
1. The fan is a Pulse Width Modulation (PWM) fan and connects to the mainboard with 4 wires - red, black, green, blue. According to allpinouts.org these wires are for 12v (5v for this particular laptop fan model number), ground, sense and control respectively.
2. The fan speed cannot be manipulated in any way in the laptop BIOS or in software. I have researched this extensively and it absolutely cannot be done.
In my attempt to try to understand what the Green and Blue wires are for, I have tested the behavior of the fan when one of these wires is disconnected and then again when both wires are disconnected. This is what I observed:
1. The fan runs at full speed (3rd level) when only the Red, Green and Black wires are connected.
2. The fan runs at full speed when only the Red and Black wires are connected.
3. The fan alternates on/off continuously at a rate of once cycle per second when the Red, Blue and Black wires are connected.
I then did some more research and came upon some information that suggested that I may be able to achieve my goal by soldering a resistor in line with the sense (Green) wire. I suppose the theory is that by soldering a resistor in line with the sense wire, you effectively make the computer think it's cooler than it actually is, where the amount of resistance on the sense signal determines when the 1st speed level kicks in. In the link above the person has used a 17k Ohm resistor, however the closest I had was a 10k Ohm so I used that instead. The result was the same as above where the fan alternates on/off continuously at a rate of once cycle per second when only the Red, Blue and Black wires are connected.
I then proceeded to do the same thing except this time soldering the resistor in line with the tach (Blue) wire. Unlike my experimentation with the Green wire above, I tried this with a 75ohm, 1k ohm and 10k ohm resistor. In all cases the temperature which the 1st speed level kicks in is the same as when no modification is present. Similarly, the temperature which the 2nd and 3rd speed levels kick in is also the same as when no modification is present.
So now I have given up. I have accepted that I really have no idea what the blue and green wires actually do and which one is responsible for controlling the speed of the fan. Therefore I am reaching out for further knowledge and recommendations from you. If you can please answer these questions and tell me what I need to do exactly to accomplish my goal I would be eternally greatful.
I have a laptop with a fan that has 3 speed levels. The speed level that the fan runs at is dependant entirely on the temperature of the CPU. When I turn the computer on the fan is completely off. As the temperature of the CPU rises, the 1st speed level kicks in. At this speed the fan is barely audible. If the computer is placed under load, the CPU temperature continues to rise and the 2nd and then eventually the 3rd speed level initiate. Both of these speed levels are loud and annoying.
I have confirmed that the CPU will operate below the maximum temperature threshold under full load for a long period of time on just the 1st fan speed level. Therefore my goal is to modify the fan such that it is off by default and then spins up to the 1st speed level when the CPU begins to heat up under full load. I do not ever want the fan to initiate the 2nd or 3rd speed level.
I have done some research into accomplishing this goal, but my lack of knowledge of electronics is hindering my progress. Here's what I know so far:
1. The fan is a Pulse Width Modulation (PWM) fan and connects to the mainboard with 4 wires - red, black, green, blue. According to allpinouts.org these wires are for 12v (5v for this particular laptop fan model number), ground, sense and control respectively.
2. The fan speed cannot be manipulated in any way in the laptop BIOS or in software. I have researched this extensively and it absolutely cannot be done.
In my attempt to try to understand what the Green and Blue wires are for, I have tested the behavior of the fan when one of these wires is disconnected and then again when both wires are disconnected. This is what I observed:
1. The fan runs at full speed (3rd level) when only the Red, Green and Black wires are connected.
2. The fan runs at full speed when only the Red and Black wires are connected.
3. The fan alternates on/off continuously at a rate of once cycle per second when the Red, Blue and Black wires are connected.
I then did some more research and came upon some information that suggested that I may be able to achieve my goal by soldering a resistor in line with the sense (Green) wire. I suppose the theory is that by soldering a resistor in line with the sense wire, you effectively make the computer think it's cooler than it actually is, where the amount of resistance on the sense signal determines when the 1st speed level kicks in. In the link above the person has used a 17k Ohm resistor, however the closest I had was a 10k Ohm so I used that instead. The result was the same as above where the fan alternates on/off continuously at a rate of once cycle per second when only the Red, Blue and Black wires are connected.
I then proceeded to do the same thing except this time soldering the resistor in line with the tach (Blue) wire. Unlike my experimentation with the Green wire above, I tried this with a 75ohm, 1k ohm and 10k ohm resistor. In all cases the temperature which the 1st speed level kicks in is the same as when no modification is present. Similarly, the temperature which the 2nd and 3rd speed levels kick in is also the same as when no modification is present.
So now I have given up. I have accepted that I really have no idea what the blue and green wires actually do and which one is responsible for controlling the speed of the fan. Therefore I am reaching out for further knowledge and recommendations from you. If you can please answer these questions and tell me what I need to do exactly to accomplish my goal I would be eternally greatful.
. This also has the unfortunate side-effect of making the fan run all the time, albeit at a low speed. You can try keeping the blue wire connected which in theory, would allow the mobo to regulate the fan but the maximum speed would be set by the voltage on the red wire.
