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H80 Fan Speed Issue


edmerf

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I connected the 2 fan cables to the pump unit. The pump unit outputs are connected to CPU_FAN input of mb and a molex connector. My issue is the fan speeds doesn't change/alternate depending on CPU load and temperature. At bios post, the fans spin at the highest speed for a few seconds and go back to normal. The problem starts here. The profile button works and when I change the profile, the fans speed up or down instantly depending on the selected profile. Also fan speeds stay constant.

 

Let's say that my initial profile is the 1st one at startup. After bios post let's assume that fans spin at 1000 RPM. The problem is this speed doesn't change when temperatures rise or CPU is at max load. When I press the profile button and select the 2nd profile, fan speeds jumps to lets say 1500 RPM as soon as I pushed the button and stays there forever. The same goes for the 3rd profile.

 

Normally one would expect that fan speed should alternate depending on the CPU temperature. I have seen a fan speed - CPU temperature graph for this cooler. It states that fan speeds do change in each profile but with different ratios and low - max speed values. However this isn't the case for me.

 

Btw I have made up the RPM values and I use stock fans that came with the unit.

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Normally one would expect that fan speed should alternate depending on the CPU temperature. I have seen a fan speed - CPU temperature graph for this cooler. It states that fan speeds do change in each profile but with different ratios and low - max speed values. However this isn't the case for me.

 

You might assume this after years of other fan controls, but it is not actually how the fans work in this system. If you look closely at those temp vs speed graphs, you will see the maximum fan speed occurs around 40C. That would just barely above idle for a CPU temp. The fans are linked to the coolant temperature inside the unit (H80i Temp) and this is the attribute they can change. The evenness of your fan speeds are exactly what is supposed to happen with a water cooling system. The fans do not need to respond to every blip and movement of the CPU.

 

This is a common misunderstanding for a lot of people coming from years of board and air coolers controls. The fans on the radiator cannot cool the CPU or affect its temperature directly. Heat is transmitted through the lid, TIM, and cold plate into the water stream. The cooling system then transports it to the radiator so it can be dumped out of the case. The temperature of the coolant (H180i Temp) does have an indirect effect on the CPU temperatures. Heat flows through the cold plate both ways, so the coolant temperature is effectively your minimum CPU temperature. By keeping the coolant temp as low as possible, you keep the CPU temps as low as possible. In fact, all coolers work this way, including air towers. The difference is a water system can hold a good amount of heat at one time without adversely affecting CPU temperatures. An air tower or little fan cooler can be overwhelmed in seconds. This is why the fans do not need react and you can keep them at fairly low speeds, even when the CPU hits a load. If the load is sufficient or lasts long enough, that will raise the H80i Temp (usually quite slowly) and the fans will increase in speed to compensate. You can only lower the H80i temp to point where you started (the ambient temperature inside the case). If your starting H80i temp at idle is 32C, no matter what you do with the fans, you will not be able to go lower than 32C under load. Keep that in mind when setting fan speeds. If your starting h80i temp was 32 and your are currently at 36C, then the most you can lower CPU temps is 4C with maximum fan speed. Most of the time, max fan speed is a poor trade for -4C core temp.

 

You do have the option of setting the fan control group to CPU package temp. However, you will then need to make you own fan curves. The default ones will be horrifyingly loud at idle and obviously the water temp scale is inappropriate for CPU temperature. I recommend you give it a try with water temp for a while. It is a better control system with lower fan speeds and less volatility. There are some set-ups where it might not work, but if you have the H80i rear mounted as exhaust, it should do well. The H80i is part of your exhaust system, one way or another. When you have a GPU load, this will heat up the rear of the case and some of that will affect the H80i temp. Your fan speeds will increase with gaming in a gradual fashion, not because your CPU is in danger, but to increase the exhaust flow in the that area.

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