Fan Controllers

Sometimes you need more fan headers than your motherboard provides or you're looking for a way to control your fans outside of BIOS. This is where a fan controller comes into play. There are many options of varying features, functionality and cost.

Basics

First you need to determine what kind of fans you have. Check the plug for the fan. If there are 4 holes then it's a PWM fan. If there are three then it's a more basic fan.

Voltage controlled Fans ( 2 or 3 pin ) are controlled by varying the voltage given to the fan.

PWM Fans ( 4 pin ) are controlled by a specific wire. The faster a signal blinks on and off on that wire the faster the fan spins. The power connections are used to just power the fan. The third is to report the fan's current speed to whatever is controlling the fan. These can still be controlled by varying the voltage but have much smaller ranges where that is effective.

Molex fans have headers that are physically larger than the others and you'll usually find a matching one coming from your power supply. These can be treated the same as a voltage controlled fan. You just need to make sure that your fan controller supports Molex fans. This is becoming quite rare so you may need to acquire a few 3 pin to Molex adapters

3 pin fans will work in 4 pin headers. They may or may not be able to be controlled. You will generally want all of your fans to be the same type, or at least the same type plugged into the same header.

Fan splitters

The cheapest option you can get. These take one fan header on your motherboard and turn it into two, three or even more fan headers. The motherboard will still be able to control the speeds of the fans to make sure you don't cook anything but all the fans connected to the one header will be controlled the same.

Keep in mind the power is supplied by your motherboard. If you try to plug too many fans into one header you will underpower the fans. If you try to pull too much power you could damage your motherboard. A good rule of thumb is 2-3 fans per header. Above that look at getting a dedicated controller.

Examples: Silverstone CPF01 PWM Fan Splitter Cable | StarTech TX3SPLITTER 6" TX3 Fan Power Splitter Cable F-M | Silverstone CPF04 1-to-8 PWM Fan Hub

Hardware controlled

These are physical devices that sit in one of your drive bays ( usually your 5.25" bay ) and has manual controls for you to manipulate like knobs or sliders. These will allow you to control different fans differently but will not allow your PC to ramp their speed up automatically during stressful workloads. They can come with different features like a couple USB hubs, an SD card reader or more headphone jacks.

Examples: NZXT SEN-MIX2 Sentry Mix 2 Fan Controller | DEEPCOOL ROCK MASTER V3.0 | AeroCool Touch 2100

Software controlled

These are also physical devices but they can be stored inside your case to not take up a 5.25" bay ( for CD drives, for example ). They allow you to manually set speeds using software or set fan curves to change speeds based on temperature of your components.

Examples: Corsair Link Commander Mini | NZXT GRID+ V2

Software only examples: Speedfan ( support is hit or miss )

How many fans can I plug in?

Now is the time we get math-y.

Remember this formula: V*A=W

We'll assume our fan controller can supply 30W of power on a channel ( the NZXT SENTRY MIX2 can ). We need to know how much power our fans pull. The Noctua NF-F12 uses 12V of power at 0.05A. Plug these values into the formula above ( 12*0.05=W ) and you get 0.6W. Now divide the power from your controller by that number ( 30/0.6 ) and you will get how many fans one channel can power. This will hold true for your motherboard headers as well.