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Fans slow down when I lock screen

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Hi All,

I am building a pc, with a I9-9900K and  I have a H150i AIO and 12 Fans that are managed by the AIO Comander Core and a Comender Core XT, has MB I have a ROG Strix Z390 e-Gaming. If I run a bench mark like Prime95 and then lock the PC, all the fans  slowdown and then the temps spike up.

I already changed the power profile to the one on the images, but I can't seem to be able to keep the fans spining while on  the screen is locked. Does any one know if this is possible todo and how can I acheive this?  

Many thanks in advance :-D



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When you lock the PC, you cut the components and controllers off from the CUE control software.  This forces the controllers to revert to their "hardware settings" saved to the device.  The H150i Elite Capellix (and it's controller the Commander Core) should be able to read H150i Temp (coolant temp) without CUE.  Make sure fans on that controller are using fan curves with that set as the control variable.  If you are using the presets (quiet/balanced/extreme), make your self an editable copy.  Go to cooling tab + and create a custom curve.  A graph appears below.  The three presets are part of the 4 shape tools in the lower right corner and will be revealed when you hover over them.  Pick one and set-up as you need, with the "sensor" set to H150i Elite Temp.


The Commander XT is harder since it does not have a native control source.  The intended one is a 10K thermistor wire.  I am not sure if that controller comes with one in the box, but they are cheap and any 2 pin version should work.  Depending on what fans are on that controller and their purpose, you can position it to read exhaust air temp (rear slot works well) or if they are somehow connected to the CPU cooling for these runs you can put it on the exhaust side of the CPU radiator and it will be effectively mimic coolant temperature -- just like the Commander Core.  


Another possible way to address this is to set up a fixed fan speed profile for this kind of work.  Pick the highest speed you are willing to tolerate and set up a specific CUE profile with the fan speed set to Fixed RPM or Fixed PWM %.  These are available in the custom curve mode.  These should hold on the lock screen, but I do not have a working H150i and Com Core to confirm.  

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 Hi c-attack,

Thanks for the help. I had the fan porfile feeding on the first core, makes more sence to have it to the H150i Ellite Temp.

I've been testing the AIO and the coolant temps (given by the H150i Ellite Temp) do not progress in the same relations has the CPU core temps. What I mean with this is I may have cores temps at 80C while the coolant is still at 35 C evem after 1H of stress test. I know that the coolant takes more time to get to a stable temp position but was expecting the coolant to go higher than 40C when the in stress test, Is this normal?

The below image is an example of what I mean, it is a 15 min run with Prim95 and once can see the coolan temps at 35 while the CPU cores range from 73 to 82 C.

Many thanks


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yes it's normal. The CPU temp is mostly governed by your Vcore, more than what cooler is attached. CPUs have very focused heat, in a very small area so there will always be a big difference.

Compare this to watercooled GPUs where density is smaller, and they have huge dies, these things run like 10°C above the water temperature.

So that difference you see is normal, and actually pretty good for Prime on a 9900k. You'll see more gains if you tweak the CPU voltages, but Prime being so extreme, you won't see those temps in normal use.

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Hi LeDoyne,

Thanks for getting back to me on this situation. The CPU is already tweaked and what is keeping the temps down is th enegative AVX offset that is set to 10. On My CPU I've tested other numbers, but this was the value I could get the CPU below 90 C during long periods.

Thanks for your help


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13 hours ago, movepage said:

I've been testing the AIO and the coolant temps (given by the H150i Ellite Temp) do not progress in the same relations has the CPU core temps.

Correct and that is how it's supposed to work.  The fans help remove heat from the cooling loop, but they do not directly impact CPU cooling at the first stage.  That part is all conductive.  So if I put a 120mm AIO, a 240mm AIO, a 360mm AIO, and some massive external wall sized array --- then start Prime 95 --- they all will have the exact same CPU temp for a short while.  It's the continued supply of heat (watts) from the CPU vs the ability to remove it from the coolant stream that creates the differences in cooling.  The little 120mm maybe can handle 250W for a few minutes and the coolant level will increase by a large amount (for example + 20C).  The massive external array may never show an increase in coolant temp because it can remove the heat as fast as it's added.  So while the CPU started at 80C with prime 95 in both examples, the 120mm climb up to 100C and the big external unit stays at 80C indefinitely.  This is what creates an advantage for one cooler vs another.  Differences in conductivity are rare and very small.  You need to get into high end custom parts to see differences there and they still will be small.  


It will depend on your voltage and clocks, but I'll guess your 9900K is about 225W during Prime.  That would be a typical coolant change at around +8C with fans around 1200 rpm on a 360mm AIO.  So the difference between a light fan speed like 900 rpm and something like 1500 rpm is going to be about (+15C vs +6C).  If you want to stay at 90C and below, I think you need at least 1200 rpm steady.


With fixed loads like Prime 95, I typically use fixed fans speeds anyway to help me differentiate environmental changes from an actual problem.  Using fixed fan speed is one less variable.  For day to day use, there is not going to be a lot difference with small changes to fan speed vs low-mid level temperature.  So an easy way to set up the curve for coolant temp is set a minimal speed you find acceptable to your normal baseline temps (likely between 25-30C depending on room temp).  Then set the highest fan speed you are willing to tolerate to the highest coolant temp you see.  That could be Prime 95, but for most users this actually during gaming if they have a large air cooled GPU.  That will heat up the case and cause a larger increase to coolant temp than the actual CPU waste heat during gaming.  Don't over think the fan speed too much.  Small changes have little effect on actual CPU temp and coolant and CPU temp have a -1=-1C relationship.  Reducing the coolant temp by 2C only reduces CPU temp by 2C.  Most of the time it is not necessary to go chasing those small changes.  

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