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 Post subject: Using a PWM splitter cable, while retaining RPM readings
PostPosted: Tue Feb 04, 2014 5:56 am 
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Joined: Wed Jun 18, 2008 1:07 am
Posts: 26
Location: Denmark
Hi everyone

I recently bought an ASUS M597A R2.0 motherboard, and to my disappointment, it seems that the PWM case fan headers don't support less than a 60% duty cycle, while the CPU supports 0% duty cycle.

I have an Antec P180 case, and I've bought 3 Noiseblocker Multiframe S-Series M12-PS Fan 120mm PWM fans (600-1500 RPM) - one for the CPU, one for back-of-the-case exhaust and one for the bottom chamber - a single Noiseblocker Multiframe S-Series M8-P 80mm PWM fan that blows air out through the PCI grill.

I really want for the case fans to be able to down to 600 RPM, when the system isn't being used, but I also really want to be able to read the fan speeds, so I can see how everything's going.

I know a PWM splitter cable will let me control all the fans using the CPU PWM header, but unless I connect the RPM pin to each of the case fan headers, I won't be able to read the fan speeds.

Are there any cables available that let me do this? I assume it's sufficient to use a splitter that splits the CPU fan header into 4 PWM headers, and then for each of the case fans, let the RPM signal run to the respective case fan header.


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 Post subject: Re: Using a PWM splitter cable, while retaining RPM readings
PostPosted: Tue Feb 04, 2014 7:13 am 
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Joined: Tue Nov 02, 2004 12:22 pm
Posts: 1815
Location: Guatemala
The only way would be to route the rpm cable to another header individually, that said i just wanted to test connecting an external 12V PSU to a fan and wanted to see the rpms the fan was going so decided to use a splitter with the rpm going to the a motherboard, but i never got a reading on it, not sure if it need the power/ground also to be connected for it to be signaling the mobo to read.

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 Post subject: Re: Using a PWM splitter cable, while retaining RPM readings
PostPosted: Tue Feb 04, 2014 8:42 am 
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Joined: Wed Jun 18, 2008 1:07 am
Posts: 26
Location: Denmark
Abula wrote:
The only way would be to route the rpm cable to another header individually, that said i just wanted to test connecting an external 12V PSU to a fan and wanted to see the rpms the fan was going so decided to use a splitter with the rpm going to the a motherboard, but i never got a reading on it, not sure if it need the power/ground also to be connected for it to be signaling the mobo to read.

That's what I'm in doubt of as well. Is connecting the RPM signal alone to the header in question sufficient. Sounds like it maybe isn't. Some guy reported success getting an RPM reading from a fan connected to a PWM splitter in another thread:

viewtopic.php?p=522782#p522782

Perhaps you're right, in that you need to connect the fan in question to the header's power/ground and sense/RPM pin, and then only route the PWM signal to the fan. That worked for him at least.

If this is the case, then the attached diagram for a Y "RPM splitter" should work for this, as far as I can tell.

You buy a PWM splitter, and for each case fan that you want a RPM reading for, you connect the fan to this RPM splitter. You connect the 4-pin connector with PWR+RPM+GND to the motherboard header that you want the RPM reading to show up on, and connect the PWM part to one of the female 4-pin connectors on the PWM splitter. As far as I can figure out this should work.

EDIT: Updated the diagram. The 4-pin connector that you connect to the fan is male, and the two connectors you connect to the motherboard and PWM splitter, respectively, are female.


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 Post subject: Re: Using a PWM splitter cable, while retaining RPM readings
PostPosted: Wed Feb 05, 2014 10:46 am 
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Joined: Tue Nov 02, 2004 12:22 pm
Posts: 1815
Location: Guatemala
Im probably going to do more testing on the weekend, although im not sure ill have the time.... depends on the family.

My theory is that the motherboard is not reading the rpms becuase its not completing the circuit of powering a fan, so if this is true.... then ill have to hack a fan to remove its cable and connect two fans, one that will be connected to an external PSU (7V in my case wallwart) and the second fan will be a 3pin (with with the rpms signal cable removed and replaced with the fan that im testing rpm line). Another thing is to test on my MSI maybe its an Asus issue, from what i remember they had like smart pin readers, like so maybe on MSI i can by pass this.... will see, if i have the time ill test it on the weekend.

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GameMi >> MSI Z87-GD65 | Intel Core i7-4790K | Thermalright Silver Arrow IBE + 3x Noctua NF-A15 PWM @500rpms| Crucial Ballistix Sport 32GB DDR3 1600 | nVidia GTX780 + ARCTIC Accelero Xtreme IV | Samsung SA850 27'' 2560x1440 | Samsung 840pro 512GB | Hitachi 7K1000 1TB | Fractal Design Define R4 + 4x Noctua NF-A14 PWM @450rpm | SeaSonic SS-860XP2
Other builds ---> ServeMi | CamMi | MiniMi | HTPCMi


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