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Discussion Starter #1
I bought a PWM fan to use on my 1080ti. Currently I have it partly running off a motherboard PWM header. Partly, because only the control line and sensor line go to the motherboard header while the 12V line and ground line go to a 4-pin molex connector.

What I'd like to to is connect the control line and sensor of the fan to the 1080Ti so I can tie control of the RPM of the fan to the GPU temp instead of the CPU temp (which hasn't been working out well).
Does the control line of a PWM fan sink much current? I'm guessing the current sinked by the PWM control line of the fan increases with RPM, but would it be the same regardless of what fan is connected?

I'm not worried about ground loops because both the 1080Ti and the molex connector would have common power grounds, although I'm not sure about PWM signal grounds. Would this be something to worry about?
 

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Quote:
Originally Posted by 8051 View Post

I bought a PWM fan to use on my 1080ti. Currently I have it partly running off a motherboard PWM header. Partly, because only the control line and sensor line go to the motherboard header while the 12V line and ground line go to a 4-pin molex connector.

What I'd like to to is connect the control line and sensor of the fan to the 1080Ti so I can tie control of the RPM of the fan to the GPU temp instead of the CPU temp (which hasn't been working out well).
Does the control line of a PWM fan sink much current? I'm guessing the current sinked by the PWM control line of the fan increases with RPM, but would it be the same regardless of what fan is connected?

I'm not worried about ground loops because both the 1080Ti and the molex connector would have common power grounds, although I'm not sure about PWM signal grounds. Would this be something to worry about?
You can use the PWM and rpm leads on GPU fan header no problem.
All PWM control circuits use same standards.

I've been doing it for many years now and helping others do the same. We've never had a problem.
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4th & 5th tutorials in this link are PWM control using GPU header.
http://www.overclock.net/t/1491876/ways-to-better-cooling-airflow-cooler-fan-data/0_20#post_22319246
 

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The PWM signal sinks very little current, and realistically you could get 3-4 fans off one signal. They tend to run FET's with a voltage controlled, not current controlled, so they need very little current. The problem comes in because these PWM lines usually have pull up resistors, which when paralelled up, eventually stress the PWM chip, which can only sink so much current from the pull up resistors. But of 2-3 fans? it'll be fine.

As for ground, the system is running off the same ground from the PSU, so there is no issue there either. Ground loops only become an issue in audio applications, which can cause hum and other unwanted noise. But for powering fans? Not an issue.

And the current sinked my the PWM line is the same, it's always on or off, so current or no current. While the AVERAGE current would change, the current drawn when on or off would stay the same.

Hope that is helpful.
 

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Realistically we can run 8-10 fans on a single PWM signal from motherboard or GPU PWM circuitry. Proof of this is the number of fan headers on PWM splitter fan hubs like Swiftech, Silverstonetek, etc .. most have 8 PWM headers.
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I have never ran more than 5 PWM fans off off a GPU fan header, because that is 2x 140mm case inteke fans and 3x 90mm GPU cooler fans. I rarely use case exhaust fans but use intake fans that are powerful enough to push air all the way through the case.
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8-10? Cool! I thought it may be a few, but went for a safe number, since every fan will be different, and potentially have different pull up values. The PWM chips I reckon could sink 10mA-20mA (maybe more depending on the chip) so I thought 3-4 would be a safe bet. See I was worried cos some fans may use BJTs rather than FETs, and would probably draw more current out of the PWM line.
 

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Quote:
Originally Posted by latelesley View Post

8-10? Cool! I thought it may be a few, but went for a safe number, since every fan will be different, and potentially have different pull up values. The PWM chips I reckon could sink 10mA-20mA (maybe more depending on the chip) so I thought 3-4 would be a safe bet. See I was worried cos some fans may use BJTs rather than FETs, and would probably draw more current out of the PWM line.
You can get all technical, but reality is 8 fans on a single signal is rarely a problem. I learned many years ago to take techical spec data with a large dose of salt and pay more attention to the results in application.
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There are some fans that won't work with even 3 fans on a 1 signal (example is some Corsiar fans). But they are the rare exception..
 

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Discussion Starter #7
The Arctic Accelero Xtreme III documentation I have has a blurb saying that newer Nvidia cards don't use PWM fans but voltage controlled fans. But why would you need a 4-pin header for a voltage controlled fan? Thanks for the replies.
 

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Quote:
Originally Posted by 8051 View Post

The Arctic Accelero Xtreme III documentation I have has a blurb saying that newer Nvidia cards don't use PWM fans but voltage controlled fans. But why would you need a 4-pin header for a voltage controlled fan? Thanks for the replies.
Possible 2x rpm leads? This would allow GPU to know the if one fan was not spinning and post a fan warning.
 

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Discussion Starter #9
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Originally Posted by doyll View Post

Possible 2x rpm leads? This would allow GPU to know the if one fan was not spinning and post a fan warning.
But there are three stock fans on the Gigabyte Gaming OC. That brings up another interesting issue, what are the fan header pin-outs for the Gigabyte 1080Ti Gaming OC?

At this point I'm thinking of just giving up and running the Delta 92x38mm on the 1080 Ti flat out at 6000 RPM.
 

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Quote:
Originally Posted by 8051 View Post

But there are three stock fans on the Gigabyte Gaming OC. That brings up another interesting issue, what are the fan header pin-outs for the Gigabyte 1080Ti Gaming OC?

At this point I'm thinking of just giving up and running the Delta 92x38mm on the 1080 Ti flat out at 6000 RPM.
My answer was a guess. That is why it had a question mark at the end.
tongue.gif

I don't know what the 'Gigabyte Gaming OC' is, but I'm guessing it's the Gigabyte 1080TI Gaming OC? Sorry but I have no idea what the fan header pinout is.
 

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Discussion Starter #11
Quote:
Originally Posted by doyll View Post

My answer was a guess. That is why it had a question mark at the end.
tongue.gif

I don't know what the 'Gigabyte Gaming OC' is, but I'm guessing it's the Gigabyte 1080TI Gaming OC? Sorry but I have no idea what the fan header pinout is.
Thanks Doyll, you already helped me out enough getting the fan to work off the motherboard PWM controller.
 
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