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120mm Case fans, Voltage question.

Last response: in Components
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December 12, 2012 7:48:50 PM

I currently have three stock 120mm case fans, one as an air intake, one as an exhaust, and one on the side (that I am considering leaving off). I had noticed that the intake fan was much louder than the others, so I cleaned them and switched them around, and whichever one I had as the intake fan was horribly loud.

The intake was always the only one connected directly to a 3-pin connection on the motherboard, the other two were connected via molex adapters which used the yellow and black which I believe is 12V. I always believed that the less voltage, the quieter it would be?

I was considering something like this: http://www.amazon.co.uk/BitFenix-20cm-Molex-3-Pin-Adapt... which would make them all 7V, with the assumption that it would make my system quieter, now I have my doubts. How much voltage is the motherboard 3-pin providing?
a c 243 ) Power supply
a b V Motherboard
December 12, 2012 7:52:59 PM

Possibly, some make new noises when undervolted
12v
a b ) Power supply
a b V Motherboard
December 12, 2012 8:00:47 PM

Motherboard headers may be either wired directly for 12V or hooked to a voltage regulator on the board to allow software-controlled voltage/RPM.

The 4-pin CPU header provides 12V and uses the PWM pin to modulate fan speed.
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December 13, 2012 11:50:09 AM

I went with this in the end:

http://www.amazon.co.uk/BitFenix-20cm-Molex-3-Pin-Adapt...

When plugged into the 12V molex, the 120mm fans aren't the loudest thing in my system, the only loud fan is the one plugged into the mobo, so this will allow me to plug all 3 into 1 molex, and hopefully far tidier than the chain of unsightly molex to molex extensions with a 3 pin spliced in I am currently using.
December 13, 2012 12:38:10 PM

I would suspect the front gets louder because the intake mesh is tighter, causing the fan to work harder (or possibly it doesn't have enough torque when it gets up to speed to fully overcome air resistance, and so the motor is skipping). It's also possible the exhaust is more powerful, and is pulling air in faster than the intake want's to go.

If you haven't, try adding the side intake in, it's always good to have more intake than exhaust (keeps the case from sucking dust in through every open hole). If there are any filters on the front, try removing them.
December 13, 2012 2:49:49 PM

djscribbles said:
I would suspect the front gets louder because the intake mesh is tighter, causing the fan to work harder (or possibly it doesn't have enough torque when it gets up to speed to fully overcome air resistance, and so the motor is skipping). It's also possible the exhaust is more powerful, and is pulling air in faster than the intake want's to go.

If you haven't, try adding the side intake in, it's always good to have more intake than exhaust (keeps the case from sucking dust in through every open hole). If there are any filters on the front, try removing them.


Whichever fan is plugged into the board is loud, regardless of position (even tested out of the case).

The fan on the side had always been used as an exhaust for my graphics card, but my new card (GTX 460) is dual slot with an exhaust of its own, which is why I considered leaving this fan off, do you still recommend that I redirect this to an intake? I must admit I had considered it.

My PSU fits at the top, my side fan sits below my graphics card, and my graphics card sits central in the case.
December 13, 2012 4:13:14 PM

Top and rear fans should be exhaust, the rest should be intake, and you should try to have more intake than exhaust (so that openings in the case have air being pushed out rather than being sucked in).

Side fans usually don't do a lot (depending on the case), so if you have an extra front intake slot, that would probably be more impactful than having the side fan, but it shouldn't hurt to add it otherwise.

As far as the noisy fan goes, can you simply use a molex to connect it then? (It doesn't quite make sense why it would matter how it's connected, but if you can just avoid the issue then why not).
a b ) Power supply
a b V Motherboard
December 13, 2012 4:34:29 PM

If fans connected to the motherboard systematically get noisier than the same fans connected directly to 12V regardless of where/how they are mounted, it could be that the motherboard is modulating power for whatever reason (could be faulty) and is causing irregular movement which translates into extra noise.
December 14, 2012 7:43:19 AM

make sure that you have the 4 prong fans plugged into 4 prong plugs. I had that switched around in my setup and it made the 4 prong fan really loud because it was getting strait power with no regulations on how much it was getting. (I also picked up a fan splitter at fry's so that I can put 2 3 prong fans on one input. Its a great little thing and I would highly recommend it if you plan on having more fans than your motherboard supports.
December 14, 2012 11:31:38 AM

My BitFenix adaptor has arrived, they are all connected to the molex now and with a new SSD my system is very quiet and a lot tidier. I'm a little concerned that my aging motherboard could be developing faults (like InvalidError said), but aside from an issue with that fan it is working.

When I have a bit of money I might replace my mobo (which would also mean I'd want DDR3), but I've spent more than my budget for now.
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