Custom 3-Pin Fan Splitter w/ RPM Tach Switch for Auto/Full Speed

Ninjutsu · Jun 5, 2013

I could'nt get my hands on a 3-pin Fan Splitter. So I'm making myself one from two of this 3-pin extensions:

Based on this diagram.

The positive and negative wiring are the easy part. But what if i put a switch on the RPM Tachometer wire?

Which is the exact same switch on the Silverstone 180mm fan (AP181) which came with my case.

Most fan splitters i see on the internet have the RPM Tach wire only on 1 fan and rest only on positive and negative. So i am basing from that.

But for 2 fans only.

I will be connecting a 120mm(from Corsair H60) and the 180mm(Silverstone AP181) fan on this. The 120mm with RPM Tach wire.

Now my hypothesis is that turning the RPM Tach switch off would give the fan full speed as there are no sensors. Turning it on would make it on Auto mode.

Now the questions are:
1. Is it fine to put different sized fans on 1 fan connector of a Mobo?
2. Will turning the customized RPM Tach Switch on and off for Auto/Fullspeed work?
3. Will it be safe to switch it on and off while the PC is powered on? For game mode or minimal use.

This is my build:
http://ninerfive.wordpress.com/

cdburner5911 · Jun 5, 2013

I may be wrong here, but it is my understanding that the tach wire is simply to count the RPM of the fan, and no motherboards (that i know of) can control the fan speed without a PWM wire
but one thing to be careful of, if you have a CPU fan, i think it is supposed to have tach output so the motherboard knows it hasn't failed

As far as different fans on one connector, as long as they don't draw too much current it should be fine (I don't know what the limit would be, but 2 should be no problem)

if you are handy with electronics, you could have your switch switch in a resistor to slow the fan down

Ninjutsu · Jun 5, 2013

thanks for the quick reply, cdburner

Molex adapters don't have a tach terminal, so am hoping Mobo would give it on default voltage.

The 180mm fan seem to have a resistor on its low speed, but i would not put one on the 120mm. As constant Auto mode would seem more viable if i where to slow it down. As it would be like putting a resistor on a auto regulated fan. It would supply more voltage to get the same desired RPM.

3pins nowadays auto regulate fans through voltage supply thus not needing the 4th pin anymore. 3pins are without power loss and electrical noise disadvantages.
http://www.tomshardware.com/forum/266476-29-difference-3pin-4pin-connectors

If the tach switched off would kill the fan might as well turn it on all the way or ditch the switch

if you are handy with electronics, you could have your switch switch in a resistor to slow the fan down

just a hobbyist

cdburner5911 · Jun 5, 2013

hmm, that does make sense, I guess I just haven't seen a motherboard that does that yet.
I learn something every day =P

If you wanted to make this into a (harder and more expensive) project, you could build your own op-amp powered speed control with temp input =P
Just some random speed control I came across on google
I just scanned it, so it may not be exactly right, but you get the idea =]

Best of luck, whichever way you go

Ninjutsu · Jun 10, 2013

I guess I just haven't seen a motherboard that does that yet.

After a quick review on my MoBo is indeed a 4 pin. Mistook it for some 3 pins on my fans and H60 CPU pump block.

So off go my switch. Did a simple clean splitter. Then tried to squeeze everything on my rig and my Video Card was too wide for the 180mm fan installation on top of the case :heink:

if you are handy with electronics, you could have your switch switch in a resistor to slow the fan down

Resistor then would to the job.

Will continue this project on my next free time.

Thanks again cdburner5911

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Custom 3-Pin Fan Splitter w/ RPM Tach Switch for Auto/Full Speed

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