Mobo PWM fan speed issue

passey89 · 10 Nov 2015 at 17:38

Just purchased one of these from OCUK

AK-CBFA07-45

All working perfectly fine. all plugged into system fan 3 header only problem if no matter what setting i set system fan 3 to (normal / silent / max) the fans all go at full rpm 2,500.

Ok it's not a problem for temps my gpu is loving the 2 X EK varder 140mm 2500rpms 5.2mm H2O blowing onto it just im kind of turning deaf in the process.

Any ideas why the mobo isnt controlling speed?

Its reporting 2500rpm in the bios as well.

wazza300 · 10 Nov 2015 at 18:01

are you setting it to voltage control in the bios for the fans?

passey89 · 10 Nov 2015 at 18:10

wazza300 said:
are you setting it to voltage control in the bios for the fans?

Dont get the option

3rd system fan speed control options are. Normal, silent, max, manual

But none of them make a change

PuzzlezAFC · 11 Nov 2015 at 02:09

passey89 said:
Dont get the option

3rd system fan speed control options are. Normal, silent, max, manual

But none of them make a change

i have the same issue on my asus sabertooth 990fx r2 mobo so i would also like to know how to set it to voltage control, as of right now im using the cables that come with my fans to reduce them to 7v

freddie64 · 11 Nov 2015 at 05:06

Could it be the pin out is different from the CPU?

passey89 · 11 Nov 2015 at 08:59

Stopped using th akasa cable and just a 2 way splitter and it controls the speed perfectly.

Tealc · 11 Nov 2015 at 13:06

passey89 said:
Stopped using th akasa cable and just a 2 way splitter and it controls the speed perfectly.

That's because those Sys fan headers only allow voltage control.

The Akasa PWM splitter does not support voltage control as the power comes from a Molex, not the header itself.

Onto the next issue. Your fans are rated at 0.7A each, so that's a potential current draw of 1.4A. Your fan headers are 'probably' rated at 1.0A. Do you see a potential issue?

You should not really use a splitter for such power hungry fans. Unless you can verify the actual current draw at max speed I'd be very cautious. Motherboard header fan control circuits are not generally something that you can replace if you blow the crap out of them.

passey89 · 11 Nov 2015 at 13:30

Tealc said:
That's because those Sys fan headers only allow voltage control.

The Akasa PWM splitter does not support voltage control as the power comes from a Molex, not the header itself.

Onto the next issue. Your fans are rated at 0.7A each, so that's a potential current draw of 1.4A. Your fan headers are 'probably' rated at 1.0A. Do you see a potential issue?

You should not really use a splitter for such power hungry fans. Unless you can verify the actual current draw at max speed I'd be very cautious. Motherboard header fan control circuits are not generally something that you can replace if you blow the crap out of them.

Whats the best solution then to control 5 pwm fans automatically?