AK-CB002 PWM fan splitter doesn't work

[thewhat]

I tried using this splitter for a PWM fan I have at home (still waiting for the other fans), but the fan always spins at full speed.

I can see the rpm in Speedfan, but I can't control the speed. If I connect the fan directly to the motherboard, it works fine and I can control the speed. Tried with a different PWM fan, same.

It's a simple device, so apart from some wires/connections not being ok there's probably nothing that can be broken. But sometimes one can miss the most obvious thing, so I'm wondering if there's something I could check/try.
Also, which wire(s) would be responsible for this not working?

 

[zagood]

If you're got the PWM plug in the motherboard header and the power molex connected, should be fine. Maybe try the fan on a different connector, but I doubt that's it.

There may be an issue with Speedfan adjusting the fan speed. See if you can get the BIOS fan speed control to work. What motherboard?

Otherwise, it may just not work. Contact Akasa directly and see if they've got any ideas.

p.s. it's the blue wire(s). And what fan?

 

[thewhat]

I've contacted Akasa and I'm still waiting for a response.

I've read of another guy for whom it didn't work.
He mentioned that it's because the motherboard supplies voltage change and not PWM to the fan.

Does this make sense and could this be the cause?

Of course, the power (voltage?) does get delivered differently using this splitter: with the splitter, the power comes from the molex (black and yellow wire), not from the motherboard.

The MB is a P55A-UD4. I can choose PWM or voltage in BIOS, but only when I have the automatic fan speed enabled. (I have it disabled, so that I can control speed freely with Speedfan.)

I've tried with a couple different PWM fans: Intel i5 stock and Slip Stream from the Mugen.

 

[thewhat]

I went and installed Easy Tune (from now on: ET) and I was slightly surprised by what happened.
I was actually able to control the fans with ET and the Akasa splitter. (Which wasn't possible with Speedfan, no matter the settings.)
It looks like ET can communicate with the motherboard in a way that Speedfan can't.
So I'm guessing that ET's messages are pure PWM to the fan, while Speedfan's messages get "translated" and arrive to the fan as voltage scaling, not as PWM. Therefore, for a fan to react to Speedfan it has to be connected to the motherboard with the power/current carrying pins (which is obviously not the case when using this splitter).

BTW, with ET I could get to much lower RPM than with Speedfan, which seems more proof that ET control is actual PWM. With Speedfan the fan would stop spinning under about 500 RPM.

So it's all good? Sadly no, for two reasons:

1. I don't need this splitter for the CPU fan, but for the case fans. The second 4 pin connector on the motherboard (for the case fans) can't be controlled by ET and I don't even know if its 4th pin is for PWM (it says 'reserved' in the manual) - but it does work with Speedfan.
Possible solution:
I could connected the CPU fan directly to this second 4 pin connector and use Speedfan for it. Then I'd connect the two case fans with the Akasa splitter to the CPU connector and use ET for them. Kinda clumsy running two programs and running wires where I didn't want them to, but it would work.

2. ET control only works if I have the Smart Fan Control in BIOS enabled. This means that the motherboard itself will also control the speed of the fan connected to the CPU connector (according to CPU temperature etc.). While this might be fine if I had a CPU fan on it, it doesn't make as much sense for the case fans (which should mostly react to GPU temperature, in my case).


So, I'll see what I'll do. At least I learned something new and it might come handy to somebody else.

I might get a different splitter, like this one:
http://www.gelidsolutions.com/products/index.php?lid=2&cid=11&id=31
Since it carries the power/current from the motherboard I'm assuming it should work with Speedfan. But please correct me if I'm wrong.

 

[zagood]

Thought it might be something like that. Kind of sucks, but work around it...

Try hooking all three up on the CPU header and letting the mobo take care of it. If something's going to be stressing your GPU, it's probably going to stress your CPU as well, so those fans should ramp up when appropriate.

The Gelid one would probably work, but I'm thinking that any standard 3-pin splitter would probably do the same thing in your situation (and be cheaper). Either way, make sure whatever fans you put on there are low-power.

 

[thewhat]

Yeah, I think I'll just get a couple of 3 pin fans and a 3 pin splitter and it might turn out just fine. I now tested with 3 pin fans and I can indeed control the speed with Speedfan.

The problem with hooking all 3 fans to the CPU header and using ET is that I wouldn't have as much control over the speeds as if I had when using Speedfan. They would either spin too slow on idle if I set them to be quiet (not cooling the HDDs etc.) or be too loud on CPU load if I set them to actually cool the components.