How many fans can i run off my power supply?

AtillaTheHung · Sep 26, 2015

I have a thermaltake 600 power supply running an msi 990xa-gd55 motherboard, 8 gigs ram, gtx 550ti video card, blue ray dvd player, and 7 120mm fans. I have an Antec 1100 v2 that holds a total of 10 120mm fans. Since the motherboard only lets me control 2 fans, I will probably connect the rest via molex so that they run at 100% power. My question is how many fans can i run off a molex string such as 2 per molex back to back or else im going to run out of plugs with all these fans especially if i go overkill and put in the other 3 120mm fans.

RememberThe5th · Sep 26, 2015

Depends how much does AMP's draw your 3x120mm fans.

JackNaylorPE · Sep 26, 2015

Molex is good for about 7 amps.....a typical 1200 rpm 140mm fan will pull about 0.15 amps.... so about 40 fans. Tho you'd have no speed control.

If you have a PWM MoBo Header, I would use one of these. It will allow your MoBo to control 11 3 pin DC voltage fans from a PWM MoBo header

http://www.newegg.com/Product/Product.aspx?Item=N82E16811984004

Connect SATA cable to Hub for power
Connect PWM cable from MoBo to Hub
Connect up to 6 fans w/o splitters

IIRC, it comes with 2 splitters so you can do 8 fans, .... if ya need more splitters
http://www.newegg.com/Product/Product.aspx?Item=N82E16812987007

If you have only DCV headers available, you can use up to six 1250 rpm 140mm fans, off the MoBo header which are typically rated for 1 amp. The rule of them I use, in order to allow for inrush current:

1200 rpm fans - 0.84 amps (~ 6 fans x 0.14 amps)
1800 rpm fans - 0.67 amps (~ 5 fans x 0.14 amps)
2400 rpm fans - 0.50 amps (~ 4 fans x 0.14 amps)

Check manufacturer web site for fan current.

Do not connect the DC power cable to the hub if using DCV headers as the 12volt signal from PSU will render the variable voltage signal from the MoBo meaningless.

photonboy · Sep 26, 2015

Ten fans is waaayyy overkill IMO, especially with only a single GTX550Ti.

Here's my suggested layout:

1) 1xCPU fan (CPU header)

2) 1xTop/Rear case fan exhaust (inline with CPU)

3) 1xFront INTAKE

4) 1xSide INTAKE

(You can use a fan Y-Splitter and control two fans at the same time such as the FRONT and the SIDE fans. You can also use the CPU case exhaust split to the CPU fan so both being controlled by the CPU header though it depends on the fan... you want similar or preferably identical specs such as 800RPM to 1800RPM, PWM.)

If the fans are non-variable then just use the MOLEX if that's easiest.

*There is simply NO POINT in putting in ten fans, and running them at 100% power? You mean full speed and possibly NOISY? If so, I especially do not see the point.

There's a huge drop-off in cooling performance as you add fans. Ten fans is pointless when four case fans setup properly can be silent and cool sufficiently (I can't speak for the CPU cooler fan or power supply or graphics card just the case fans).

JackNaylorPE · Sep 26, 2015

It sounds like OP is moving from a case with 7 fans to one that holds 10 fans. If you already own the fans makes sense to use them .... after all 7 fans at 800 rpm is better and quieter than 4 fans at 1500 rpm. The extra 3 fans, per my reading, are not on the table at this time, but for potential future usage, perhaps to be used in case of a GFX card upgrade.

I do agree that running 24/7 at full speed is undesirable. Frankly I would find the noise extremely annoying. I have sixteen 140mm 1250 rpm fans

Right now ....

(6) Case fans on PCB 1 are off.... when fan curve calls for rpm to drop below 350 rpm, they shut off.
(6) fans on PCB 2 for 420mm radiator are at 325 rpm
(4) fans on PCB 3 for 280mm radiator are at 325 rpm

When gaming, they get up to about 650 rpm.... when under stress testing, they can get to low 800s

Fans are inaudible until they reach about 900 rpm

Fan curves were set up using 6 internal temperature sensors and a fog machine to observe air flow. I was unable to reach a drop off in performance however. Setting fan speeds manually to 1250 rpm maximum, does the following:

Coolant Delta T drops from 12.3 to 8.4C
CPU (31% OC) temps drop from 72 to 68C
(2) GPU( 26% OC) temps drop from 44C to 39C

However, at 1250 rpm you can hear the fans ... at 850 max, you can't tell if the system is on. I'd rather have the silence than the 4C. The only draw back from silent system is when you come in the morning at hit the power button to turn on the machine when it was never shut off from the night before

No, I wouldn't buy 7 fans for a single GPU build but if I had them already, I wouldn't leave them in a box in the closet. But I wouldn't think of installing any fan in any box and allowing it to run full speed 24/7

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How many fans can i run off my power supply?

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