What are the different types of fan

[almoststew1990]

I'm looking for new fans for my h100i which I've had a while. These will be going on a Bitfenix Pandora ATX. But I'm a bit confused between the different fan types and when people say "yeah Noctura is really good" and I go to look and there are at least 10 different types of fan it gets confusing, so please can someone clear up / confirm the following before I hit the go button on my order?

PWM- 4 pin, speed is controlled by the motherboard / fan controller. Based on volts or temp? Why wouldn't we want this??

3 Pin- spins at max RPM all the time unless it has a built in speed selector?

Max RPM- I see some are rated at 1500RPM, 1800RPM etc... is this the maximum speed they will spin at (regardless of whether they are a 3 or 4) or does it effect the whole fan profile (i.e. if a fan controller tells 2000rpm fan to spin at 50%, under the exact same conditions the fan controller would be telling a 1000 rpm fan to spin at 100%)

Why do some fans not say a RPM 'rating'? This fan for instance has three settings.. will this be controlled automatically? or is there a physical switch somewhere?

Static Flow- sounds like an oxymoron to me! 'good for radiators / heatsinks' how can you tell if a fan is a SF fan if it doesn't say it in the description (are the blades different or something)

And then you have fans that look like this with very steeply angled blades and fans that look like this with shallow blades, and then you have the industrial range which is different because 'reasons'...

I've been building PCs for nearly 10 years and fans are the final frontier so to speak!

 

[Telecaster]

Noctua's various fan speeds are controlled by way of an in-line resistor, they give you three with the fan and you just pick which one to use depending on which max fan speed you want.

 

[ErikN]

pwm/3pin:
Different types of speed control, usually PWM can have a bigger operating range as the fan is always fed 12 volts and is instead speed controlled by rapidly turning the power on and off. Voltage control does exactly what it says, changes the voltage. PWM fans can also be controlled with voltage though PWM control is preferred.
Most motherboards have both voltage and PWM controllers, usually the chassis fans headers are voltage controlled, and the cpu fan connectors are PWM.



Max RPM:
Max RPM is indeed the max speed, when fed a continuous 12 volts. Usually also come with a range, like +-10%, meaning a 2000rpm fan can have a max as low as 1800, and as high as 2200rpm.

How fast the fan actually spins at a specific output can differ, fan controllers simply output the amount of power, be it voltage or PWM, you, or ex. a temp curve, tell it.
For example, I have a bunch of EK vardar F4 2200rpm PWM fans in my computer, my fan controller is currently outputting 37% power on one of the channels, this causes these particular fans to spin at 517rpm, so a bit lower than around 800 rpm, which is 37% off 2200.



Static flow(pressure) is a unit of measure on how good a fan is at pushing air though a restriction (like a radiator).
To compare static pressure to air flow, think of a garden hose:

If you just want to water the lawn, you are only interested in getting as high flow as possible to spread it over a large area, but as it is just going to fall down on the grass you dont care as much about the pressure = High air flow for chassis fans, where there are almost no restrictions.

But, if you want to clean dried mud off the stone plates on the walking path, you want high pressure to really get in under the mud spots and wash those away = High static pressure for ex. radiators, lots of fins that restrict the flow.



As for fan designs there are mostly there for noise reduction purposes, or other areodynamic reasons beyond us mortals knowledge.


Finally: Industrial fans are, as the name suggest aimed mainly at industrial use, where noise levels are rarely an issue, but instead there are demands like high reliability in a 24/7 operating situation, or high resistance to ex. dust and/or water in dirty environments.
Industrial grade fans are usually a lot more expensive than consumer grade fans.

 

[almoststew1990]

Thanks that's a very useful summary!