I am trying to make my own fan controller for a pc that I am building. The main part of this circuit would just be a potentiometer in the path of the 12V line from the power supply to limit the current through the fan. However, I would like to add an interval on timer to the circuit to short around the pot on start up, so the fans get the full 12V to ensure that they start spinning. I have done a lot of searching on google, and I haven't been able to find an example circuit for this type of timer. I tried my best to make my own with a MOSFET, but I have no idea if it will actually work, or just burn down my house. If anyone could lend some expertise, I would appreciate it.

Fans:
12VDC, 0.15A, 1.8W, 3 pin

Power Supply:
Just a standard 600W, 80+ bronze supply with short protection



I attached a picture of my circuit. The goal was to use a capacitor to switch a mosfet off. The circuit would allow current initially, and when the capacitor charges, the first mosfet would switch off, which would switch off the second mosfet. I put this into a circuit simulator and it did work, but I still would need to use this in the context of the whole project.

 

Why two MOSFETs? You could just use one to control the fan.

Using a pot to control the fan is not the greatest idea, but it can work. You'll need the right pot, one with a low ohms range and rated to handle at least the power rating of the fan. That might cost more than a PWM fan controller you can buy very inexpensively these days, which would also solve your startup issue.

 

I have to agree with wayneh. If you look at your fan specifications you see that 1.8 Watt and on average these fans draw about 2 Watts so you really need a low resistance potentiometer but at least a 5 Watt pot so it doesn't run smoking hot. PWM is likely the best method to control fan speed and when you get right down to it I can go to NewEgg and look at Fan Speed Controllers which come in assorted flavors for less than I can build one for.

If I did want to run full speed for a short period I would likely use a One Shot powered off the 5 Volt SB supply and trigger off the power on button of the PC. The PWR_ON is a momentary logic low so the same line which triggers the PSU Start could also trigger a 555 (or similar) One Shot or maybe a PIC Chip like a 8 pin 08M2 PICAXE. Have that trigger a logic level MOSFET and bypass the fan speed controller. Anyway, as mentioned a pot really is not a good way to go. Matter of fact I would think about doing it all in one using the same PICAXE chip. They can do PWM.

Ron

 

Just one P ch. MOSFET, S to + 12, D to fan, G to cap. like in your drawing.

 

I am trying to make my own fan controller for a pc that I am building. The main part of this circuit would just be a potentiometer in the path of the 12V line from the power supply to limit the current through the fan. However, I would like to add an interval on timer to the circuit to short around the pot on start up, so the fans get the full 12V to ensure that they start spinning. I have done a lot of searching on google, and I haven't been able to find an example circuit for this type of timer. I tried my best to make my own with a MOSFET, but I have no idea if it will actually work, or just burn down my house. If anyone could lend some expertise, I would appreciate it.

Fans:
12VDC, 0.15A, 1.8W, 3 pin

Power Supply:
Just a standard 600W, 80+ bronze supply with short protection



I attached a picture of my circuit. The goal was to use a capacitor to switch a mosfet off. The circuit would allow current initially, and when the capacitor charges, the first mosfet would switch off, which would switch off the second mosfet. I put this into a circuit simulator and it did work, but I still would need to use this in the context of the whole project.

What is the goal of your project?

The Bios in your PC with throw an error and not complete the startup if the CPU fan is not working.
Most modern motherboards use pulse-width modulation to control fan speed. What different result are you looking for?