Using LL120 fans instead of H55 rad fan?

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sami_z_r

Apr 28, 2018
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Hey what's up?

In order to make my build more colorful I bought 3 Corsair LL120 fans. Can I replace the rad fan from the Corsair H55 with one of the LL120? Or will it affect the temperature? I have an I7 8700k installed in a SPEC04 case. Thanks!

Note that I won't be overkilling the cpu (or overclocking it any time soon for that matter).
 
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Karadjgne
Yes, it'll affect your cpu temps, but not exactly how you expect.

The stock h50 fan is 3pin analog. That means when it's plugged into the cpu_fan header, it runs 100% of the rated speed at all times. The LL120 is pwm. That means it'll change rpm with the cpu temp. So at idle speeds, it'll slow down considerably, be much quieter, but the temps will be artificially higher.

Also, the fan designs are slightly different, they'll have different pressure and airflow and that affects radiators differently. When I changed out my stock H55 fan for a Noctua, it immediately got massively quieter, idle temps improved as did load temps. Just because the design of the fan is greatly more effective with a radiator. So even though the Noctua was at...
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Paperdoc

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Probably will work, but there is a possible problem. Your old fan had specs of max 57 CFM air flow with max backpressure 1.9 mm water. The LL120 is spec'd at max 43 CFM at max 1.6 mm water. So the new fan cannot deliver the maximum air flow that the old one could. Now, IF your older system never ran that rad fan at full speed anyway, this still can work. The automatic control of the CPU cooling is based on the TEMPERATURE at a sensor built into the CPU chip, so its normal action would be to raise the fan speed until it gets enough cooling to do the job. So after the replacement the system will simply run your new fan at a higher speed than the old one was, and still deliver the SAME air flow and cooling you had before. If that works well, then the only thing you "lose" is reserve cooling capacity for times when you run your system at high workloads. You may never need that much reserve.

I assume you have the rad fan plugged into the mobo CPU_FAN header. The old fan is a 3-pin design, so it will be using Voltage Control Mode (aka DC Mode) to control that fan. You probably should change that to PWM Mode, since the new LL120 is a 4-pin fan.
 
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Karadjgne

Karadjgne

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Yes, it'll affect your cpu temps, but not exactly how you expect.

The stock h50 fan is 3pin analog. That means when it's plugged into the cpu_fan header, it runs 100% of the rated speed at all times. The LL120 is pwm. That means it'll change rpm with the cpu temp. So at idle speeds, it'll slow down considerably, be much quieter, but the temps will be artificially higher.

Also, the fan designs are slightly different, they'll have different pressure and airflow and that affects radiators differently. When I changed out my stock H55 fan for a Noctua, it immediately got massively quieter, idle temps improved as did load temps. Just because the design of the fan is greatly more effective with a radiator. So even though the Noctua was at 450rpm idle, vrs h55 at full speed 1600rpm still saw a 1°C drop.

With the LL120 you'll be able to change fan curves to suit your performance needs and wants. Lowest possible temp isn't always best temp. My big aio runs silent mode, fans 650rpm. To set on performance mode increases that to 1500rpm, audibly louder and annoying. Drops cpu 3°C. Not worth the trade off.

So even if temps do change, question is is how does that really affect you, cuz it really doesn't do anything for the cpu at less than 70°C.
 
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Paperdoc

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I agree as above with one small change note. You have not told us what mobo you are using, or confirmed into which header you connected your rad fan - I assumed it is the CPU_FAN header. On many mobos now that header can detect what fan design is plugged in and change itself (if you did not make a change of settings in BIOS Setup) to use Voltage Control Mode when a 3-pin fan is detected. IF your mobo has this feature it may well have been controlling the rad fan speed properly all along, rather than running it full speed always.
 
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Karadjgne

Karadjgne

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Oh? OK, that's a new one, didn't know that. Prior, the cpu_fan header has been dedicated pwm, well for the last 10 years ± anyways. If true (it's about time!) that's a bonus.

The H55 has 2 leads, one from the fan, one from the pump. Corsair directions state the pump should be attached to the cpu_fan header and the fan to any sys_fan header. This is done for a reason. Prior (thanks paperdoc) the cpu_fan header was 12v dedicated pwm. If you put an analog device, such as 3pin fan or the pump, in that header it would have zero options but to run full 12v speed, no analog voltage control. This guaranteed that corsair wouldn't see a for bad pumps, when really it would be slow because the voltage was lowered. Also, that particular header has a safety feature, if it sees 0rpm, it will shut the pc down or fail to boot and give a cpu-fan error. Meaning if the pump fails, it shuts the pc down.

Bad thing about that hookup is the fan on a sys_fan header. In bios, the temps are set high, max fan speed doesn't happen until @70°C. Case temp. Since the case barely ever exceeds 40°C, the fan is always running minimal rpm, and you get funky high cpu temps at high loads. Ppl forget to change the bios settings to more closely resemble the case temp. It's really not a good solution, but is the best outcome for Corsair.

Me, I do it backwards. Pump on sys_fan header, change/disable bios for that header to full 12v ability, fan goes to Cpu_fan header, works as normaly should. Cpu temp goes up, fan gets faster. Alternatively, some mobo's like many of the Asus boards, have a cpu_aux header. That's a perfect header for a pump as it's dedicated 12v with no pwm or analog control.

My H55 has been purring along happily 24/7/365 for the last 5 years.
 
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Paperdoc

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What you suggest works. There is an even better option on SOME mobos.

It is ideal to connect the PUMP to the CPU_FAN header, since that is the one header that can and will shut down a system when the cooling device attached there fails. As long as this header is using PWM Mode the pump will receive the fixed full 12 VDC supply it needs. Or, if you wish, you can set that header to use DC Mode and full speed ("turbo mode?") all the time to be sure. Then, as you say, there's the problem of how to control the actual rad fan according to the CPU internal temperature. On SOME mobos for the CHA_FAN or SYS_FAN headers you can configure one to use the CPU internal temperature sensor, rather than a mobo temp sensor, as its guide. If necessary, you can examine the fan response curve pre-programmed for the CPU_FAN header and then ensure that the SYS_FAN header controlling the actual rad fan has the same response curve. This only can work if your mobo has those configuration options for a CHA_FAN or SYS_FAN header (or maybe a CPU_OPT header).
 
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Karadjgne

Karadjgne

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Exactly. Many of the more budget mobo's don't have some of those nice bios abilities, stupid things are grayed out or permanently auto, if they even are available. So hookup contrary to Corsair instructions is quite viable there. On the flip side, programs like Asus fanXpert have programmable alarms, (mine is set for 1000rpm on a 1400rpm pump) which while not as good intrinsically as a hardwired cpu function, do well since pump, fan curves, alarm, temps etc are all located in one spot and are easily set up and monitored.
 
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