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PWM splitters vs ones with molex adapters

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May 12, 2013 1:35:37 AM

So upon researching online, I've determined that having splitters used for the 4pin headers on the motherboard isn't very good in terms of putting the extra stress on the connectors. But what if say, I were to use something like this:
http://www.amazon.com/Rosewill-PWM-Splitter-Model-RCW-F...

In which power is supplied from the PSU from the molex adapter, to power say, one PWM fan and a regular 3pin one? I'll still be plugging in the 4pin female part into the motherboard for the added PWM control for the PWM fan. But would this kind of setup still put stress on the 4pin headers on the motherboard? Or are the fans taking power directly from the PSU and only using the 4pin headers on the motherboard for reading/controlling the voltage/rpms?

Edit: And another question, can 3pin fans be connected to a molex adapter that is made for 4 pin fans, like the one shown above (where there are male connectors that only have 3 pins, but if a 3pin fan were to be plugged into those, it seems to only be able to plug into 2 of the 3 prongs.)
a b V Motherboard
May 12, 2013 3:28:02 AM

Have a look at this image:
http://www.advancetec.co.uk/media/catalog/product/cache...

To answer your first question:
Two cables are connected to your motherboard. One is the PWM signal and it's split to all three male connectors (blue). This means that all three fans will be driven by the same PWM signal.
Second cable is the "sense" signal coming from the connector marked as CPU Fan (green). This means that BIOS or any software you plan to use, will report speed (RPM) of the fan connected to this connector. 12V is not taken from the motherboard connector, so there is no load on it. Fans take power directly from PSU.

Second question:
Yes, 3 pin fans can be connected to this adapter. As you can see the male fan headers of this adapter have cuts on the connector casing, allowing you to connect a 3 or 4 pin female plug only in one, proper orientation - very much so as connectors on the motherboard. In this case this two "prongs" as you called them are power (+12V, yellow) and ground (black) both coming from PSU.
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May 12, 2013 8:31:27 AM

Bejusek said:
Have a look at this image:
http://www.advancetec.co.uk/media/catalog/product/cache...

To answer your first question:
Two cables are connected to your motherboard. One is the PWM signal and it's split to all three male connectors (blue). This means that all three fans will be driven by the same PWM signal.
Second cable is the "sense" signal coming from the connector marked as CPU Fan (green). This means that BIOS or any software you plan to use, will report speed (RPM) of the fan connected to this connector. 12V is not taken from the motherboard connector, so there is no load on it. Fans take power directly from PSU.

Second question:
Yes, 3 pin fans can be connected to this adapter. As you can see the male fan headers of this adapter have cuts on the connector casing, allowing you to connect a 3 or 4 pin female plug only in one, proper orientation - very much so as connectors on the motherboard. In this case this two "prongs" as you called them are power (+12V, yellow) and ground (black) both coming from PSU.


Sounds good, thanks! So pretty much the PWM reading has no effect on 3pin fans since it only connects w/ the power and ground, thus it would always be running at 100% correct? I guess it would, since 3pin fans do not have PWM control anyway.
Also, it would be better to use those splitters that connect to the PSU directly for power in a sense right? Since the motherboard will have less load on its own 4pin headers.
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a b V Motherboard
May 12, 2013 9:49:04 AM

Yes, PWM has no effect on 3 pin fans. As you wrote, they run @100% all the time.

As for connecting multiple fans directly to PSU instead of mainboard, I think it's a good idea. I don't know how much current a 4pin fan header on mainboard can provide.
Let the fan use 2W, which gives you 2W/12V =~ 0.17A per fan. Then 3 fans require about 0.5A @ 12V. It isn't much and probably wouldn't damage the mainboard, but again, it's only my guess.
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May 12, 2013 10:06:06 AM

Bejusek said:
Yes, PWM has no effect on 3 pin fans. As you wrote, they run @100% all the time.

As for connecting multiple fans directly to PSU instead of mainboard, I think it's a good idea. I don't know how much current a 4pin fan header on mainboard can provide.
Let the fan use 2W, which gives you 2W/12V =~ 0.17A per fan. Then 3 fans require about 0.5A @ 12V. It isn't much and probably wouldn't damage the mainboard, but again, it's only my guess.


I was never good at electricity and magnetism back in physics :p . Okay, great, I'll do it that way. Thinking about getting this:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Not sure if I'll load it up with 5 fans per one molex though, probably be okay, but I'll try to split them up.
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a b V Motherboard
May 12, 2013 12:34:09 PM

5 fans at one molex is no load at all. If it were 50 I would consider splitting them.
You can use this Evercool adapter without hesitation.
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May 12, 2013 2:29:10 PM

Alright, sounds great, thanks!
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