# 4 pin PWM fan splitter cable



## Millennium (Jul 6, 2011)

Hi there
I just today got a PWM fan splitter cable off ebay. I have looked at it closely and it seems to split all 4 cables of the PWM spec and wire them all up in parallel to it's two sockets.

When I was researching these cables I was lead to believe that the tach signal wire should only be connected to one fan. Unfortunately this cable seems to connect both fans to the mobo cpu fan socket signal pin. Will this still work? Is it dangerous? 

I will give this a go when my CPU arrives for my build but it would be great to get some feedback before I wire it all up. If it comes down to it I can just cut the signal wire to one of the extension sockets to 'fix' the wire. The wire is not home made, it comes in a sealed packet so that leads me to believe it is correct... please advise.

edit: found a review of the cable saying it was 'garbage' cause it sends the rpm signals for both fans to the motherboard. Looks like I will be modding it afterall. What a stupid mistake to make in a clearly retail product...


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## mlee49 (Jul 6, 2011)

Wait, the PWM signal is sent from your motherboard not your fans. 

Which fans is this going to control? Cpu heatsink? Different fans entirely?

What exactly did you want it to do? Run a PWM control to one fan only while running the other fan at 100%? It seems pretty clear in the description(and from the picture) that this will take one PWM signal and send it to both fan headers.

I think it's totally fine to have the signal split between two fans, it's doing exactly as its intended to. 

I'm still confused as to what your purpose is, please clarify how you want to run your fans.


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## LordJummy (Jul 6, 2011)

mlee49 said:


> Wait, the PWM signal is sent from your motherboard not your fans.
> 
> Which fans is this going to control? Cpu heatsink? Different fans entirely?
> 
> ...



mlee49 is correct. It does exactly what it says. How would a dumb splitter send multiple PWM speeds through one cable to multiple fans? Its intended job is to control 2 fans at the same time with one PWM hookup.


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## scaminatrix (Jul 6, 2011)

cheesefeat's a good seller, I've dealt with him a few times before. Test it, see what it does; the guy who posted the other review might have just been a complete idiot  It won't be dangerous, just monitor temps and listen to the speeds of the fans.


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## _JP_ (Jul 6, 2011)

Millennium said:


> found a review of the cable saying it was 'garbage' cause it sends the rpm signals for both fans to the motherboard.


Exactly. It works like this: The motherboard supplies the power and the PWM signal to the connector and this is independently of the number of fans you connect to said connector (there's a limit, though). The fan, when powered and running, returns a signal (usually trough the yellow wire) to the motherboard, that gives the RPM of the fan. The more "tach wires" you have connected to the motherboard, the more RPM you'll see in the readouts. It usually adds the RPMs of each fan. You can use the method that Arctic Cooling uses with their fans, although their fans already have a sort-of splitter included. Their fans get the power and PWM signal trough one connector (usually on the CPU-fan header) and have another connector that only has the "tach wire", so that you can connect to another fan header on the motherboard (the idea is to connect it to a 3-pin header) to get the fan's RPM readout.


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## Millennium (Jul 6, 2011)

Just to clarify: I am hoping to run 2 CPU cooler fans from one CPU cooler 4 pin socket. I think I will try it out as it is, if the RPM value seems doubled or I have any other problems like the fans running too slowly I will mod the lead. I don't blame the seller, he sold me a sealed part, he would expect it to work properly. 

*mlee49* and *LordJummy* , I guess my original post was unclear. I *want* the PWM signal split properly to speed control both fans, I just want the correct RPM reported to the mobo from the fans. If the splitter causes my fan rpm reading to double I'll just mod it; no big deal!


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## _JP_ (Jul 6, 2011)

Millennium said:


> I want the PWM signal split properly to speed control both fans, I just want the correct RPM reported to the mobo from the fans. If the splitter causes my fan rpm reading to double I'll just mod it; no big deal!


By modding you cable I assume you're going to cut one of the tachometer wires. That will result in you motherboard only reading the RPMs of one of the fans connected.
And by "split properly", you mean...?


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## Millennium (Jul 6, 2011)

That's right re the mod, just cut one of the tacho wires. PWM signal split to 2 fans = fan control to both fans AFAIK. That's what I meant by split properly. Hopefully the extra load won't be a problem.


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## _JP_ (Jul 6, 2011)

Then yes, both fans will be controlled by the same PWM signal with no issues and the load of those two fans won't be a problem.


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## de.das.dude (Jul 6, 2011)

both fans can be controlled by the same PWM signal, provided the total current doe not exceed the mobos specification. or you will end up frying some transistor.

but the RPM cable wont work. it wont damage the mobo, but will give junk readings.


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