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Rewire Rosewill PWM Splitter to work with 3 pin fans?

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April 26, 2011 4:47:08 PM

Hi,

I have the Rosewill PWM 3 fan splitter,

http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...

and I have read several threads about it and understand how it works. It only works with 4 pin fans. I was wondering if it is possible to use this splitter with 3 pin fans and control the speed of the fans. Is it possible to rewire/rejig it so it could work with 3 pin fans? I only have 2 fan headers on my board (Gigabyte GA-880GMA-UD2H). I am currently running 2 Noctua fans for my CPU, no prob there but have 3 case fans, all 3 pin but only one sys fan header. Not that I need to use all 3 but is it possible and possible with this splitter? Or maybe 2 Y splitters? But then wouldn't power be an issue? 3 fans on one header with no extra power?

Or can I use just one 4 pin fan and use it as the "CPU" fan and will I then be able to control the speed of the 3 fans? I am using SpeedFan.

I apologize in advance. I am new to computer builds, know nothing about electrical and new to this site (have posted a couple of times).

Any advice or solutions are greatly appreciated.

Thanks

May 20, 2012 7:08:14 PM

No...the 4th pin is the PWM control wire. There are a variety of other ways to control 3 pin fans. There are simple pot (potentiometer type controls like this:
http://www.amazon.com/Gino-Plate-Speed-Controller-Reduc...

To complete panels for 3.5 or 5.25 bay openings like this:
http://www.newegg.com/Product/ProductList.aspx?Submit=E...

To server type solutions (which will work fine in a pc case) like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

There are 3 pin fans on the market that have built in temp. sensors that control themselves like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Also, you will want to look into the dba/CFM ratio of the fans you are buying themselves. Typically the better the ratio noise to air flow the better the fan. A lower dba and a higher CFM is what you are looking for. MOST of the fan's advertised numbers are exaggerated, so go with the customer reviews here, or buy a ton of fans and see for yourself (I haven't had much luck with the Nocturna fans moving air, but they are quiet). My personal opinion is that Sythe makes the better 120mm fans (gentle typhoons, and Kama flow 2...also a couple of the slip streams) at 92mm the Vantec Stealth SF9225L, and at 80mm the cool master R4-BM8S-30PK-R0. One fan that is typically overlooked when dealing with cooling, and noise is the power supply's. If you have a noisy PSU, it really doesn't matter what the dba on your case fans is. I could list PSUs that I've used over the years, but that is a whole different topic. For this I would also go with customer reviews as the majority of the PSU advertisements don't even mention noise factor.
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May 20, 2012 9:41:39 PM

Agreed, you cannot make this 4-pin fan adapter work for 3-pin fans. It is designed to take the full 12VDC supply from a PSU's 4-pin Molex output (for enough power to run 4 fans) to each fan, then give each fan the PWM signal taken from the CPU output on the mobo. (The fans draw very little power from the PWM signal, so having 4 share it is no problem.) A 4-pin fan uses that PWM signal to control the actual current flowing though itself from the +12 VDC supply. A 3-pin fan has no way to do this, so it will simply run at full speed if you just plug it in.

The speed of a 3-pin fan is controlled by reducing the +12VDC supply, and this adapter cannot do that. Its source of +12 VDC is fixed.

You CAN wire in parallel TWO 3-pin fans and connect them to one mobo 3-pin pinout - just do NOT connect both Yellow fan wires together. Those are the lines taking the fan's speed signal from the fan back to the mobo, and you cannot give the mobo two mixed speed pulse signals. Leave ONE of the two yellow wires not connect to anything. I said TWO such fans in parallel. Most people think that a typical mobo fan output can supply enough current to start up two fans simultaneously (that's the max current draw situation) , but probably not three.
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