Question PWM fans

Jan 12, 2021
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My question here is, can 3 pin fans work as PWM setting from bios if the 3pin fans are connected to case fan hub and from where the fan hub (4 pin) cable goes to motherboard CHA_FAN 1-3 ports, 4 pin port... I have noticed if I change my CHA_FAN 3 setting from bios- (where all my 3 case fans are connected by the one cable coming from the case fan hub) -to DC the case fans goes kind a loud. But with PWM setting they are nice quiet. Well the case fans are not "PWM fans" so it's probably clear that they are not working correct as PWM setting. But if the whole case fan hub it's PWM. I mean even the 3 pins on the hub? If using these 3 pin fans that are connected to case fan hub ports, in PWM setting from bios, could it do some damage or be bad to use? Few pictures from manual to clear it more...
https://ibb.co/C61ybnc
https://ibb.co/ZX8LvbK
 

Paperdoc

Glorious
Ambassador
They don't work that way.

The ONLY way to control the speed of any 3-pin fan is to use the older Voltage Control Mode (aka DC Mode), which means the mobo header must alter the voltage supplied from Pin #2, and NOT send out any PWM signal on Pin #4.

For a PWM type of fan, instead the header must provide a fixed 12 VDC on Pin #2 at all times, AND send out the PWM signal on Pin #4. Then a special chip inside the fan uses the PWM signal to modify the power from the 12 VDC supply and change the fan speed. But a 3-pin fan does NOT have that chip, so when you plug one of those into a header using the new PWM Mode, the 3-pin fan can only run full speed all the time.

Now, a fan HUB does NOT know any of this. Almost all do a very simple job for you. Instead of getting any power from the mobo header, it gets a constant 12 VDC supply from the PSU directly (via a SATA power cable) and sends that out on Pin #2 to all its fans. Then it gets the PWM signal from the mobo header and sends that out to all its fans, too. That way all the fans' speeds can be controlled IF they are PWM type with the special chip. If you try to plug a 3-pin fan into one of these Hubs, it is the same as if you plugged it into the mobo header, and it can NOT have its speed controlled. But NOTE in this that it only works if the mobo does supply the PWM signal to the Hub. If it does not - and it WILL NOT if you configure the mobo header to use DC Mode - the Hub gets NO PWM signal and cannot send it to any fan, so ALL the fans will run full speed, no matter which type they are.

If you have only 3-pin fans, then you cannot use any normal HUB like that. There are a few special ones that can work. But by far the easiest route with 3-pin fans is to use one or more SPLITTERS to connect fans to mobo headers. A Splitter is simpler than a Hub because it gets all its power from the mobo header and simply shares that out to its fans. A Splitter has NO "arm" to connect to a PSU power source. But is is limited by the mobo header, which can supply up to 1.0 A max current. So you need to find out the max current spec for each of your fans, and add up that for all the fans on one header via a Splitter. The total cannot exceed 1 A on one header. If you have more than one header, you can connect more fans to the next one, and the 1 A limit applies separately to the second header. Once that is done, you must go into BIOS Setup for the headers you are using 3-pin fans on, and set each to use DC Mode, and not PWM Mode. Then the header(s) can control the 3-pin fan(s).
 
Reactions: alexbirdie
Jan 12, 2021
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In the end everything still works and temperatures are very good. Just with DC Mode the case fans are a bit loud, but with PWM they are quiet you dont even hear them, but still temperatures are very good... So maybe I just forget this case fan hub and connect all my 3 case fans directly to motherboard CHA_FAN ports.... ?
 

Paperdoc

Glorious
Ambassador
You certanly can do that. There are few details that need to be configured to ensure they all work properly. For us to help, we need to know what maker and model of fans you have, and how many of them. NOT the CPU cooler system, just the case ventilation fans. Also we need the maker and exact model number of your mobo to check out the count of heades and their abilities and settings.
 
Jan 12, 2021
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You certanly can do that. There are few details that need to be configured to ensure they all work properly. For us to help, we need to know what maker and model of fans you have, and how many of them. NOT the CPU cooler system, just the case ventilation fans. Also we need the maker and exact model number of your mobo to check out the count of heades and their abilities and settings.
My motherboard: Asus Prime B550-Plus AM4
Product codePRIME B550-PLUS / 90MB14U0-M0EAY0
EAN4718017782340
UNSPSC-Code43201513
PID634117

3 x Case fans: Fractal Design Dynamic X2 GP-14 140 mm
Produc codeFD-FAN-DYN-X2-GP14-BK
EAN7350041084396
UNSPSC-Code43201619
PID414206
 

Paperdoc

Glorious
Ambassador
Thanks for that info. This will be relatively easy. To start, plug each fan into one of the three SYS_FAN headers on your mobo.

Your mobo has two manuals you can download if you don't have them already. See this first

https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/PRIME_B550-PLUS/E16536_PRIME_B550-PLUS_UM_WEB_051420.pdf

on p. 1-1 and 1-2 for the locations of its three SYS_FAN headers. They are all 4-pin headers, but you will configure them to work properly with your 3-pin fans. They WILL plug into those headers.

See here for the details of how to enter and set options in BIOS Setup.

https://dlcdnets.asus.com/pub/ASUS/misc/Manual/PRIME_TUF_GAMING_B550_Series_BIOS_EM_WEB_EN.pdf

See p. 7, and go to Advanced Mode. Choose F6 to get to Q-Fan Control (p. 10). p. 39 details options for the SYS_FAN headers, but you can use this screen to make your settings. Choose each header in turn and set them as follows
(Bottom centre) Profile to Standard
(Upper right) DC Mode
(Bottom) Click on Apply
Next, check one item not included in that screen for EACH fan header. Go to p. 39. Set Chassis Fan n Q-Fan Source to Motherboard

When you have them all set, use Esc to return to Main Menu, then click on Exit in the top Menu. See p. 49 and select Save Changes and Exit to save your settings and reboot.

This will place all three case ventilation fans under automatic control for speed based on the actual temperature measured at a sensor on the mobo.
 
Apr 6, 2020
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This will place all three case ventilation fans under automatic control for speed based on the actual temperature measured at a sensor on the mobo.
Sorry to semi-hijack the thread but I had a noisy fan(s) pretty soon after I bought my prebuilt PC (approx 4 years old now) until a week ago, and now theres' no noise. Using HW monitor it says I have 3 PWM fans at 0% so i'm not sure if they were always idle. Other than that the temps seem ok. The fans seem pretty cheap but if I replace them my temps are only hitting 54c max with idle so should I even bother? ty in adance
 

Paperdoc

Glorious
Ambassador
In general you ALWAYS need some fans to ventilate your case, and of course some fan (or other system) to cool the CPU. Your story suggests a couple of ideas.

First, if the fans always were noisy from the beginning, it is entirely possible they were always running full speed. This can happen if they were connected directly to the PSU for power (which has no way to control speed), rather than to mobo headers. It can happen if the fans are connected to a case-mounted fan speed system with a manual speed button, and you never chose to change the speeds. It also can happen even if they are plugged into mobo headers, but the header(s) they use either are configured for constant full speed, or are set to use the new PWM Mode of control even though the fans themselves are the older 3-pin design. In any of those situations, some adjustments to the system could reduce fan speed and noise.

Secondly, if you now have NO noise as a result of a recent change, and your HWMonitor tool says all the fans have ZERO speed, that's a big warning. Now, zero speeds could happen simply because the fans never were connected to any mobo header and the mobo had no speed signal to show you. But it also can happen if the fans ARE on mobo headers and HAVE failed. If that is the situation. you really do need to replace them, and MAYBE change the way they are connected and controlled. For this, you need to open your case with the power off and look inside to locate the fans. Then turn on your machine and observe the fans immediately. The NORMAL sequence is that every one of your case fans should start up right away at full speed. After a few seconds, they all should then reduce their speed to whatever is needed for a cool system, but NOT stall. Thereafter as you use it, the fans should change their speeds at higher workloads. If you do not see all of that, tell us exactly what you do see.

If you need advice on how to change, tell us these details:
What maker and exact model number is your mobo?
How many case ventilation fans do you have?
If you can, tell us the maker and model number of the fans (usually on lables on the hub). If that's not clear, tell us what the label does say in terms of Volts, Watts, and / or Amps. ALSO tell us how many wires are in the cable from the motor, and how many holes are there in the connector on the cable end?
 
Reactions: mikewhatever
Apr 6, 2020
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Thanks. I think your first suggestion that they were always running full speed seems likely. Guess that's the problem with a cheapish prebuilt PC but it has lasted 4 years :)

My CPU and GPU fans are still going and temps seem fine but I'm not doing much to push either, i'll have a look in the case later but I know there used to be a lot of air coming out of the back of the case and now there's not much. So case fans are cheap, i'll probably need more advice with the connections/cable advice for more help if the new fan doesn't help
 
Apr 6, 2020
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In general you ALWAYS need some fans to ventilate your case, and of course some fan (or other system) to cool the CPU. Your story suggests a couple of ideas.
Thanks, i splashed out and paid almost £11 for an arctic fan :) it's very quiet and there was definitely something wrong with the old fan as there's a lot more air going through the case now. Guess the old one was going full speed for no reason as you said. Appreciate the help.
 

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