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[SOLVED] Different RPM chassis fan question.

Jun 26, 2019
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Sorry if this is the wrong thread for this question. New to PC . I am building a PC that will be all air flow no liquid cooling. I will have a total of 6 chassis fans on my PC. Problem is the mother board has only 2 connections for chassis fans. So I am getting one of these Silver Stone PWM fan hubs CPF04 so that way I can have them all plugged into the hub and the hub plugged into one chassis fan header on the mother board and can all be controlled automatically by the BIOS. the fans I will have are as listed below.

4 X 140MM Noctua NF-A14 PWM RPM 300 - 1500
2 X 200MM Noctua NF-A20 PWM RPM 350 - 800

so now to my question. If I have all 6 of these plugged into the hub and lets say the one plugged into the main port is the 200MM fan that maxs at 800 RPM, when the motherboard calls for max speed and runs the fan at 800 RPM will it relay 800 RPM to the other 140MM fans that max at 1500 RPM and I not get their full potential and it runs them at 800 RPM too? Or is it sending a signal of percentage being 100% in which case I wouldn't have a problem? If it is the case of running that one at an RPM is there any other hubs that can have different RPM fans on one hub and all fans be used properly and are at their full RPM if needed?

Thanks for the help in advance.
 

Karadjgne

Titan
Herald
Yes. The motherboard doesn't call for rpm at all. Bios uses duty cycle. It's a percentage between 1-100. When the temps change, bios changes the duty cycle according to the fan curve and temp settings. Default is 70°C = 100%. If the fan is 800rpm, the pwm signal will pulse to allow 100%, 800rpm. But at the same time it'll also send the exact same 100% signal to the 1400rpm fans. Which then run at 1400rpm.

The only thing different about the lead fan is that that particular fan has the tachometer lead, that reports back to the bios, not for actual rpm readings usage, but for speed change. The rest of the fans have no tach connection in the hub, those pins are missing.
 

Karadjgne

Titan
Herald
Yes. The motherboard doesn't call for rpm at all. Bios uses duty cycle. It's a percentage between 1-100. When the temps change, bios changes the duty cycle according to the fan curve and temp settings. Default is 70°C = 100%. If the fan is 800rpm, the pwm signal will pulse to allow 100%, 800rpm. But at the same time it'll also send the exact same 100% signal to the 1400rpm fans. Which then run at 1400rpm.

The only thing different about the lead fan is that that particular fan has the tachometer lead, that reports back to the bios, not for actual rpm readings usage, but for speed change. The rest of the fans have no tach connection in the hub, those pins are missing.
 
Jun 26, 2019
5
0
20
1
Yes. The motherboard doesn't call for rpm at all. Bios uses duty cycle. It's a percentage between 1-100. When the temps change, bios changes the duty cycle according to the fan curve and temp settings. Default is 70°C = 100%. If the fan is 800rpm, the pwm signal will pulse to allow 100%, 800rpm. But at the same time it'll also send the exact same 100% signal to the 1400rpm fans. Which then run at 1400rpm.

The only thing different about the lead fan is that that particular fan has the tachometer lead, that reports back to the bios, not for actual rpm readings usage, but for speed change. The rest of the fans have no tach connection in the hub, those pins are missing.
Ah sweet thank you. I guess I don't have an issue after all. Now I don't have to worry about the RPM of the fans that are plugged into that hub! I don't know how to change this to solved otherwise I would.
 

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