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Connecting case fans to Motherboard & power supply

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January 18, 2010 10:45:34 AM

My new build has a ANTEC 300 case and a ASUS P7P55D LE motherboard. The Asus has two fans built in to the case at the top and rear. I have added two more 120cm fans at the front of the case. On my motherboard, there are three fan connectors (excluding the CPU fan connector) and these are marked as PWR-FAN, CHA-FAN1 and CHA-FAN2. I assume that I connect my fans to these connectors but which fan goes in which connector? Also this would leave me with one of the front fans unable to be connected to the motherboard. So would I connect this fan direct to the power supply?
a c 144 ) Power supply
a c 156 V Motherboard
January 18, 2010 10:50:51 AM

Plug the case fans into PSU molex connectors. That leave 2 chassis fans to be plugged into the motherboard. You should use the two CHA connectors.
January 18, 2010 11:08:27 AM


Thanks JSC. Just to confirm, the case fans are the two that I installed in the front of the case and the chassis fans are the ones already built into the case in the top and rear?
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a c 144 ) Power supply
a c 156 V Motherboard
January 18, 2010 11:17:01 AM

Well, they are all case or chassis fans. Let me rephrase: Plug the 2 fans built into the case into the molex connectors and set the speed with the little switches.

Plug the two fans you added into the CHA-FAN connectors.

a b ) Power supply
a b V Motherboard
January 18, 2010 8:41:17 PM

Do NOT plug any case fan into the mobo's PWR_FAN connector. That port is for one purpose only. If your PSU has a wire coming out of it with a "fan connector", plug that into this mobo connector; if your PSU does not have on of these, leave this mobo connector unused. What it actually does is feed a speed signal from the PSU's fan to the mobo so it can display it for you and monitor it to be sure the fan is running. It does not control that fan or provide any power supply to run a fan.

Running 4 fans from 2 mobo connectors is a problem. The simplest option is to connect 2 to Molex power outputs from the PSU, although this will run those fans at full speed all the time. If you buy (may come with your fan) a speed controller that slips into the line to each fan, you can set it to some slower fixed speed. Then you plug the other two fans into the mobo's CHA_FANx pinouts. Now, what you get from that may vary according to the mobo's capabilities. At least one of them will be under control of a speed control loop in BIOS that uses a measured temperature signal from a sensor built into the mobo. Maybe both are controlled this way, or maybe the second one is a fixed speed. Read what your manual says. In your case, I see from the specs that one of these two ports is 4-pin, and one is 3-pin. IF you have a 4-pin case fan, plug it into the right connector and it will actually use the special newer 4-pin (PWM) power supply signal there for speed control. If you have only 3-pin fans, plug them in anyway - the connectors are designed for backwards compatibility and a 3-pin fan on a 4-pin port will just behave as a normal 3-pin fan.

BUT suppose you want to connect all four fans in such a way that the mobo CHA_FANx ports can power and control them. Well, with 3-pin fans at least you probably can do this with a few limitations. The key is to recognize that the 3 wires involved are Ground (usually black), + VDC supply (usually red, and varies in voltage according to fan speed the mobo is trying to achieve), and yellow (fan speed pulse signal fed back to mobo to be read). So for one CHA_FANx mobo connector you could take two fans' sets of leads and modify them so that both are fed from one connector. You connect both black lines together and both red lines together to that the fans share the voltage supplied, simply drawing enough current to run both fans in parallel at nearly the same speed. BUT for the yellow lines, leave only ONE of them connected - leave the yellow line from the second fan connected to nothing - so that the mobo receives a pulse signal from only one fan and does not get confused. So at least you could connect two 3-pin fans each to the two CHA_FANx ports and control all of them with whatever your mobo can do in terms of control.

In the case of 4-pin fans, I suspect a similar technique could be done, but I have not done it so I'm not positive. In that case the color coding is different, so you'll have to work it out. But the essence is you must NOT connect in parallel two fan's speed signals, while still connecting in parallel the Ground lines, and + PWM voltage lines, and maybe the + VDC lines (although I believe that +VDC line is not actually used in a true 4-pin PWM fan). One thing for sure, though - do NOT try to connect in parallel a 3-pin and a 4-pin fan. They operate differently can cannot share the different signals.
January 18, 2010 10:11:43 PM

Chassis fan, case fan = same thing. Chassis and case are two different words for the same thing - the tower/box which houses all your hardware. With the antec 300, the 2 fans that come already installed have fan speed controllers, so plug these two directly into molex cables coming from your power supply. You can control the speed of these 2 fans using the switches on the fans.

Plug the other 2 fans which you installed into the motherboard connectors. Use the 2 CHA_Fan connectors for these. You will now be able to control the speed of these fans using the ASUS FanXpert that comes on the cd thats supplied with the P7P55D LE motherboard.

Now you have control over the speeds of all four of your fans. You will also be able to monitor the fan speeds of the 2 that are plugged into the motherboard using FanXpert. You can also create profiles, which will automatically adjust the speed of these 2 fans according to temperature.

January 19, 2010 6:38:57 AM

Thanks for all the info. In the end I had to plug all four of my fans into the molex conenctors from the power supply. The reason is that none of the leads from any fan would reach the connectors on the motherboard. This leaves me with two fans that I can control the speed with and two that I can't. The strange thing also that I noticed is that the two fans I added to the front of the case (XILENCE RED WING) have connectors that only have two pins inside them. I did manage to connect this to the power output 4 pin molex connectors but shouldn't the fan connector have three or four actual pins rather than two?
a b ) Power supply
a b V Motherboard
January 19, 2010 12:26:12 PM

No, two wires are all that is needed for a fan - Ground and +12 VDC. On a 4-pin Molex connector, the extra two are a second Ground and a different +5 VDC supply for other types of devices.
January 20, 2010 12:41:54 AM

if you do not mind have no speed control over the fans then you psu molex will work
October 28, 2010 9:45:32 AM

Paperdoc said:
Do NOT plug any case fan into the mobo's PWR_FAN connector. That port is for one purpose only. If your PSU has a wire coming out of it with a "fan connector", plug that into this mobo connector; if your PSU does not have on of these, leave this mobo connector unused. What it actually does is feed a speed signal from the PSU's fan to the mobo so it can display it for you and monitor it to be sure the fan is running. It does not control that fan or provide any power supply to run a fan.

Useful thread - one correction though : the PWR_FAN connector does supply power to run a chassis fan - ASUS P6X58D and HAF 932 here
February 28, 2011 12:34:26 AM

For my new computer (Big Snort, to replace Old Snort) I'm looking for a fan to suit the Sabertooth-58 "CHA-FAN1" odd 4-pin connector; serving (from bottom to top) "GND", "CHA FAN POWER", "CHA FAN IN", and "+5V"; the +5V looks as if it might be
used to set a minimum fan speed). All fine except I can't find a fan to plug into the 4-pin. I want a 120mm fan I can just snap into an Antec 900 case and have it work just fine in a CHA-FAN1. I've been looking for such a fan for several weeks but haven't found one -- does anyone know of such a fan?

Of course, if I get stuck with only three wires from a fan I could flange up a 4-pin cable with a couple of diodes to assure that there would always be voltage to
the fan either from CHA FAN PWR or from the +5V buss; but I thought I was
past my melted-lead period...

June 5, 2012 1:22:15 PM

Paperdoc said:
No, two wires are all that is needed for a fan - Ground and +12 VDC. On a 4-pin Molex connector, the extra two are a second Ground and a different +5 VDC supply for other types of devices.


Molex pin: 1 = Yellow = ground
2 = Black = 7 Volt
3 = Black = 12 Volt
4 = Red = 5 Volt

Nr 2 is middle speed
Nr 3 is High speed
Nr 4 is low speed
June 5, 2012 1:36:05 PM

There is a video on youtube that shows my point.. Don't be shocked its a kid from around 10 years =) OOh I know that only two wires needed to make it work but if there is a 3 or 4 wire on the fan means it has its use..
!