Question How to safely control computer fan speed without damage to the hardware?

sxk1277

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Mar 19, 2020
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I've figured out how to control fan speed using the software speed fan. For an experiment, I want to start from fan being stopped to slowly increase the fan speed. However, I'm not sure which fan is cpu fan as I'm aware cpu fan should not be off under any circumstance. How do I safely do this experiment without harming my pc? I've total 2 fans but can also attach another fan.

Thanks :)
 
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Paperdoc

Glorious
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There is a very simple way to do what you say you want, but that depends whether that really IS what you want. IF you really want to have control of the fans yourself, rather than letting your machine do it all for you, that is a different matter.

Your mobo has automatic fan speed control systems already, and you can set it to use those and not have to worry. For that you do NOT need Speedfan at all. You do need to know how to get into your BIOS Setup system, make a few adjustments (maybe) and save them. If you tell us the maker and exact model number of your mobo, we can look up its manual and advise more precisely.

For now, a general explanation. We all talk about automatic fan speed controls by the mobo. But in reality each of them is a TEMPERATURE control system. It monitors an actual temperature from a sensor on the hot item, and then manipulates the speed of a cooling fan aimed at that item to keep its temperature near a good target so it does not overheat. As you change your workload and the heat generated causes temperaures to rise, the fans automatically speed up (or slow down) to keep up with the cooling needs. You do not have to do any work for this. These systems also do added tasks, like making SURE the fan starts up at boot time, and checking to be sure the fan has not stalled, etc., and sending you a warning if a fan fails. Part of this also is never to send the fan a signal to stop and, conversely, to force the fan to re-start if it ever does stall. (A few mobos allow you to let the fan stop at low temperatures and re-start when needed, but that is not common.)

In your mobo there will be at least two separate fan control systems. One uses the CPU_FAN header (and maybe a related one) to control cooling of the CPU. Its basis is a temperature sensor inside the CPU chip. The other (there may be more than one) is for case ventilation fans, and its basis is a different temp sensor built into the mobo. SOME mobos may even have extra temp sensors on special components on the mobo, but you do not usually need them.

Each fan header is configured separately in BIOS Setup, and there are several items for each. You may have an option to disable a header if you have nothing connected to it.

(a) PROFILE is the type of strategy used to determine what speed the fan shuld run. Its options include usually Standard or Automatic (continuously monitors the relevant temperature sensor and uses that to decide the fan speed using a pre-defined "curve" of speed vs temp), Turbo for always full speed, Quiet for always slow speed, and Custom or Manual (similar to Automatic, but allows you to set your own "curve" specs).
(b) MODE is the method it uses to send signals for speed control to the motor. Options are Voltage Control Mode (aka DC Mode) required for 3-pin fans, or PWM Mode ideal for 4-pin fans.
(c) SOURCE may allow you to choose which temperature sensor this header pays attention to.
(d) ALARM may allow you to set a lower limit for fan speed to trigger a failure alarm, or perhaps an upper temperature limit for this sensor to trigger an alarm.
 

sxk1277

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Mar 19, 2020
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I was hoping to avoid bios method because it works upon restarting and it is too slow. I wanna implement many different speeds of fan and see the results right away.
 

Paperdoc

Glorious
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OK, then there is another tool you can use. I agree, BIOS Setup is an "off-line" tool you cannot use while working. But virtually every mobo comes with a CD of drivers, etc AND some utilities. Many of the utilities are actually installed for you at the time you install the mobo drivers from that CD. One of these usually is an app you use just like any other under Windows, and it gives you ways to observe many items about the mobo such as temperatures, voltages, fan speeds, etc. It also lets to SET many items like fan options without going into BIOS Setup, so you can observe and change while working. In other workds, it does a lot of things like Speedfan can do, but it is custom-designed for YOUR mobo and should be reliable. See if you can find that and try it.
 

sxk1277

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Mar 19, 2020
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I dont wanna risk frying my computer though. I wanna start this experiment with fan speed set to very low and then increase from there. I don't wanna accidentally touch cpu fan either. I use XPS 8700
 

Paperdoc

Glorious
Ambassador
OK, that's a Dell product, and the manual for it makes NO mention of any utility on a CD. Maybe they don't provide one, so you will have to continue using Speedfan. Before you do, be aware that some third-party utilities like that can give you wrong readings until they are calibrated for your mobo. So just be a bit skeptical.

Now, your main concern is how to identify the CPU cooling fan and be sure NOT to change its operation. There are only two fans in this system - the CPU fan and the rear exhaust fan plugged into the SYS_FAN1 header near the top rear of the mobo. To start, arrange your things so you can reach into the case and disconnect that cable from the rear fan from its SYS_FAN1 header. But don't do that yet. Leave the side cover panel off. Start your machine, and get Speedfan going. See exactly what it tells you about the fans in your system, and what names it gives them. Now reach in and unplug that rear fan, and watch to see that it does stop while the CPU cooler continues to work. Now look at what Speedfan is telling you. You should be able to recognize which fan now has zero speed. THAT is the fan you can try your experiments with. Leave the other fan alone - it is the CPU cooler. Now you can shut down your system. Re-connect the rear fan to its SYS_FAN1 header. Note that it has ridges down one side, and the header has a plastic "tongue" sticking up beside its pins. The side ridges slide around that "tongue" so there is only one way to plug it in.
 

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