Question Are all cases fans compatible (as long as he size is the same?)

[JamesC01]

I need to replace my case fan, it's not spinning properly. I've had this problem for years, and fix it by just manually spinning the fan, and that would usually get it to start spinning properly, but it's just not happening anymore. The fan is 12cm (measuring the whole thing, including the enclosure of the fan. Can I just buy any old 12cm case fan, or do I need to do more specific searching to make sure I get a compatible one? Will all the mounting screw line up? Will the cable fit? Do I need to worry about power consumption? Could buying a fan that's too powerful be bad?

 

[Paperdoc]

Basically, yes. There are a FEW items that need some attention.

FYI, that size labels on fans is the dimension of ONE SIDE of the square fan frame. All fans of the same size will have mounting holes of the same diameter and spaced exactly the same. So the all should fit.

Fans are almost all in either of two designs. The older ones come with a cable with three wires and a female connector on the end with 3 holes. It has two ridges running down one side just beyond the span of the three holes. It plugs onto a mobo male header with 3 pins and a plastic "tongue" sticking up beside them. The ridges on the fan connector slide around that tongue, so there is only one way to plug in. The only way to control the speed of such a fan is to vary the VOLTAGE supplied to the fan from Pin #2 of the header, ranging from 12 VDC for full speed to about 5 VDC for minimum speed without stalling. (Standard fan pinout is Pin #1 Ground, Pin #2 + VDC power supply, Pin #3 fan speed signal consisting of 2 pulses per revolution, 5 VDC, sent by the fan back to the header for counting). It is common to call these "3-pin fans".

The newer fan design uses a fourth pin and hole in the connectors. Electrically and mechanically these are designed as similar as possible so you CAN plug either fan type into either header type and it will work (with a small limit). On the fan's female connector those two ridges are in the same place, so the 4th hole is outside the span of those ridges. In this type of fan the power supplied by Pin #2 of the header is always 12 VDC, and the fourth pin supplies a new PWM signal. Inside the fan there is a small chip that uses that signal to modify the flow of current from the fixed 12 VDC supply line through the motor windings to achieve speed control. These fans are called PWM fans or 4-pin fans.

Here's the small limiting detail if you mis-match types and that IS allowed. If you plug a 3-pin fan into a 4-pin header that is using the new 4-pin PWM signal system, that fan receives from Pin #2 a constant 12 VDC supply. It cannot receive any signal from Pin #4, and it has no special chip anyway so it could not use that signal. So it always runs full speed, giving you lots of air flow for cooling but no control over that. If you plug a 4-pin fan into a header sending out the older Voltage Control Mode kind of signals, it gets no PWM signal so its chip cannot modify anything. BUT the power supplied from Pin #2 now is VARYING from 12 to 5 VDC, so the speed of the fan IS controlled.

These days on mobos ALL the fan headers have 4 pins. However, in the configuration options fo each header in BIOS Setup, you have a choice of whether the header behaves as a modern 4-pin one called "PWM Mode", or as an older "Voltage Control Mode (aka DC Mode) suitable for 3-pin fans. Many also have an "Auto" option that testes whatever is plugged into that header on each start-up and sets itself to the correct Mode.

For your case, OP, either fan design could be used. IF the fan you are replacing is a 3-pin design, or IF the mobo header available has only 3 pins, you should look for a 3-pin fan. While you could use a 4-pin, they typically cost a bit more and this is not the optimal way tp power and control a 4-pin.

For every fan, the actual flow rate of air it generates depends on its speed, of course, but also on details of the fan blade design AND on the resistance to air flow caused by objects in the fan's path. So for any one fan if you plot a graph of actual air flow rate versus the backpressure it is dealing with (that is a measure of air flow reistance), you get a VERY ROUGHLY straight line from max air flow with NO reistance (backpressure), down to NO air flow with a certain max backpressure, Any nore backpressure means absolutley NO air flow. Fan specs published will show these as two items: Air Flow (usually in cubic feet per minute) at NO backpressure, and Pressure (in inches of water column) at which all air flow is stopped. Fans to be used for more interference with air flow (such as through the fins of a heatsink on a CPU air cooler, or though a radiator in an AIO cooler system) must be designed for higher backpressure conditions, whereas case ventilation fans generally face only low air flow resistance or backpressure. So commonly LOW pressure fans for cases are rated with "pressure" specs of under 1.0 inches water, and "pressure" fans are rated from 1.0 to 3.0 or higher. Typically the "pressure" fans will promise max air flow at NO backpressure slightly lower than "air flow" fans, but they can still deliver adequate air flow at higher pressures when "air flow" fans give up.

A lot of people focus on fan SPEED. Do not. The important item is AIR FLOW, so look for that spec while bearing in mind the Pressure spec against your planned use.

Regarding power consumption you probably need not worry, but here are more details. As a quick starting point, almost all fan headers will supply power at 12 VDC max up to a limit of 1.0 A current. Some may have higher specs in the mobo manual.

FIRST, backgound on fans with lights, since these are now so popular. There was (and still are around) an early lighted fan design with only one colour of lights in the frame and NO way to control it. These are called LED Fans and they simply have some LED lamps in the frame connected in parallel with the motor windings so that they are lit whenever the fan runs, and their brightness tends to dim as the fan is slowed down. For these you need to be a little more careful because those lights add to the max power the fan can draw from the header. Fans with NO LIGHTS in the frame today typically are rated to use 0.10 to 0.25 A max current draw, and most in the lower part of that range. A fan's specs certainly should show that value. The older LED Fan type can draw up to 0.40 or even 0.50 A.

Today's LIGHTED fans come with two different lighting types in them, but BOTH are designed with the lights completely separate electrically from the fan motors. For this reason they have TWO cables with different conector designs on their ends; one is the normal fan motor cable / connector, and the other is a wider connector that goes to a different mobo lighting header. So ONLY the MOTOR max amperage rating is relevant to max load on the moobo fan header. (Similarly, there is a limit on power avilable from the mobo lighting header for the lights, but that is not pertinent to your inquiry.) However, sometimes makers of lighted fans fail to provide clearly separate specs of max current draw for motor and lights. BUT if the specs are not clear, the "rule of thumb" for the MOTOR ONLY in these fans still is 0.10 to 0.25 A max per fan.

You CAN buy fans with very high air flow ratings that draw a much higher max current, but few people need such fans for normal computer cases. For example, a typical 120 mm Noctua 4-pin fan will consume 0.10 A max at very good air flow, while their high-performance iPPC model will deliver 1.8 times that max air flow, but can consume upto 0.30 A. Beyond that you can find fans that consume over 1.0 A for one fan, but blow a LOT of air (and noise) and normally are used in large industrial cabinets and racks of data centres. For what you are replacing, OP, you will never need this!