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How 3 pin fans work

E

Excalibrax

n00b
Joined
Aug 21, 2007
Messages
53
Ok I've been thinking about a project because I'd like to control my fans a certain way.

Basically I would like to use my computer itself to control a series of fans.

Basically With motherboards from Asus, MSI, and EVGA you can control your fans that are plugged into the motherboard. I know most of these are PWM and understand the advantages, but lets face it, not all fans are PWM.

So when you have a computer controlled 3 pin fan does it like with Asus Which basically gives you control beyond 5v, 7v, and 12v. It basically gives you control to set it at different voltages say at .5v steps. Similar to a knob on a physical controller. is this how it does it, stepping the voltage?

I'm trying to gather background information as what the end goal is this. I'm going for a water cooling setup, with multiple radiators. I'd like to be able to control all the fans on one radiator to behave one way or to the software like one fan. The problem is that your talking 3-4 fans per radiator, and 6-8 if your going push/pull. with most controllers offering 20w, and Scythe Gentle typhoon ap-45 Rating highly in fan testing which require just over 6watts to startup. P = IV. Startup power needed is 0.53A .53*12=6.36 watts per fan. So at minimum your looking 19.08 watts for 3 fans, and 25.44 watts for 4, up to 50.88 watts for 8 fans.

Most Fan controllers don't support this and neither do motherboard headers. I am pretty sure I am getting an Asus board, and would love to just use their Fan Exprt 2 software. So What I am looking to do is use an arduino board as a go between and power the fans from the power supply, but have the computer think its one fan and propagate out the volt stepping to different headers.

Now I know this is overkill for a many people and may even be considered crazy. But is the Idea behind it sound? Am I misunderstanding how this software works with 3 pin headers?
 
When you use Fan Xpert ASUS software you can manually Control the speed of the fan, also in Bios can you do this too, not as accurate of PWM fans, but it offer the posibility of do in percent. so you can control minimum temp 40C=50% maximum temp 60=80% so it will be controlling the Voltage on the Fans in that range so for example if are 2000RPM at 12v it will just slowdown the voltage amount in percent to max 80% of 12V wich its 9.6V and will keep the fan running at 1600+/-10%RPM and not static 5/7/12v. better yet if you use Fan Xpert 2 which let you select different points of percents and degrees... its not accurate as PWM but it help.. in my sabertooth I use Y splitters for 2x120mm fans HDD cages and 2x120mm at front and work perfectly on the 4xCorsair AF120 so i use 4 fans on only 2 chasis header..
 
I'm hoping to solve the wattage problem I'm having and basically use the software provided to make my own fan controller, or at least a sort of repeater. in order to that I need to know how these things work. I am probably going to see about buying a few of the fans I'm looking at and hooking them up to a multimeter and check my info. I could be wrong on the starting amperage and be worried about nothing, but I could be right, and I think this would be an item that could be beneficial to some people out there as well.
 
1. 3pin fans change speeds simply by adjusting the voltage going through them. The 3rd yellow wire only supplies a signal for an RPM reading. All fans have varying startup voltages, some go as low as 5v but average 12v rated fans require 7v or more to start spinning.

2. Controlling a large number of fans through 1 channel on your average fan controller will be difficult. Finding one with a high enough wattage rating per channel will be key. There are fan controllers out there that can handle 60 watts per channel.

3. If you are wanting to control a whole bunch of fans with the built in ASUS software, you will need a device (such as a microcontroller e.g. arduino) that will plug into a motherboard fan header and read that voltage as an input. If it is a pwm fan header, the device will have to read pwm signals. Write some code that will read either the voltage or pwm output, then output a respective value to a circuit designed to power and control enough fans. In other words, Asus software->Motherboard fan header->Arduino->power circuitry->shit ton of fans running same speed. Keep in mind this is the most elaborate solution, especially since there are fan controllers out there that can handle 60 watts per channel.
 
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Here is what I've basically made an hour ago before reading your post. I'm just gathering info to make sure the idea isn't feasible.

Bascically in the Input voltage would be propagated to the other Voltage lines for fans. The CPU header is attached to one fan so it gets back accurate tachometer info and the other fans just follow suite to how fan 1 is set. The idea is to set this up to bypass the wattage limit on any fan controller including the one from the CPU and attach multiple fans.



Based on a limit of 60watts from the power supply and assuming you have the 1 fan powered by the CPU fan cable, you could probably then connect around 7-8 fans. Depending on the wattage I can output to each fan header this will determine how many connectors I would put on there, OR I might just do 7.
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The Arduino and other IC chips can only provide 5v on their digital out pins. Another problem is that Arduinos and microcontrollers can only sense 5v max. Any higher and you risk burning them out, and they wouldn't be able to detect higher voltages anyways.

What you can do, however, is use an H-bridge. By using an H-bridge, you can use the PWM control of the Arduino, and vary the voltage accordingly.

For the input voltage problem, what you would need is some sort of voltage divider to step 12v max to 5v max.
 
I think I just stumbled upon a much simpler solution.

Switftech 8-way PWM Splitter box.

http://www.performance-pcs.com/cata...e=product_info&cPath=34_451&products_id=37599


Since the speed control of a PWM fan is provided by one wire and not by altering voltages like a 3 pin fan, you can simply copy the pwm signal amongst all the fans. The 3rd wire, RPM sense, is the only thing not copied among all the fans, just the first fan. Supply one PWM signal, split it amongst all the fans, then supply as much power as you need.
 
That only works for PWM 4 pin fans, however found a Sunbeam 30W Rheosmart 6 Channel Smart Fan Controller does the what i wanted, PWM in controlls all the fans so 1 4 pin from mobo to the controller, and then is controlled by 6 Half H bridges like Tsumi was talking about.

From my idea this cuts out the IC circuit and arduino as the Arduino outputs PWM just like the MObo. So you do a PWM to Analog voltage conversion using the H bridges.
 
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