Question Some PWM Fans at Full Speed, Some Aren't

OODUMB

Prominent
Mar 29, 2020
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A while ago, I replaced all my case fans with 5 of the same model of be quiet! PWM fans, which are all connected to a DeepCool PWM fan hub, and controlled by software. They all couldn't reach the hub, and I was in a pinch and didn't have plain old 4-pin extenders, so I used a couple 4-pin splitters. At first, I tried actually using just one as intended, but all the splitter fans ran at full speed while the others didn't (only one of the three ends had a 4th pin; I assumed that fan would act as the 'master' to the other two). Instead, I used two splitters, one for each of the two fans that couldn't reach, and made sure to connect them to the ends with the 4th pin. This worked perfectly.

Fast forward to now, just after a 600 mile move. Upon starting up the machine, the two fans connected by one splitter each are at full speed again. The non-splitter fans are behaving normally. Could something have broken during the drive (we didn't hit any potholes or anything, and have done this drive before, but who knows)? Since the other fans are normal, I feel like the hub is fine, but I can't imagine a cable like this breaking, but just so that the 4th pin doesn't work, and have that happen to both splitters independently.
 

Lutfij

Titan
Moderator
Does the PWM fan hub that you sourced from Deepcool advertise being able to split from a header? Is it this? If so, then you're only going to be able to pair 4 fans to that one hub. Might want to mention what your motherboard's make and model is and it's BIOS version. I'd have suggested that you get something akin to Phantek's PWM hub that is advertised to run 12. I don't need that many in my Ethoo Evolv ITX but it's a good thing to have for a future build(if I do decide to go crazy) but to bring it back, if you were lacking the cable length, you'd either need to buy the right extenders or relocate the hub in your case.
 

OODUMB

Prominent
Mar 29, 2020
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515
0
Does the PWM fan hub that you sourced from Deepcool advertise being able to split from a header? Is it this? If so, then you're only going to be able to pair 4 fans to that one hub. Might want to mention what your motherboard's make and model is and it's BIOS version. I'd have suggested that you get something akin to Phantek's PWM hub that is advertised to run 12. I don't need that many in my Ethoo Evolv ITX but it's a good thing to have for a future build(if I do decide to go crazy) but to bring it back, if you were lacking the cable length, you'd either need to buy the right extenders or relocate the hub in your case.
The hub is a DeepCool FH-10, so it should handle all of them fine. As I said, this was all working a few days ago. And to be clear, I do have a fan connected directly to the proper port for control purposes. The MB is an ASRock Z390 Taichi, BIOS version P4.20 (7/23/2019).

My new place has a much lower ambient temperature (down from ~78F to ~67F), and I'm not doing anything to wildly intense, for for now I've disconnected the problem fans so I don't have to listen to them constantly, and I'll report back when I have the proper extensions.
 

Paperdoc

Champion
Ambassador
What you describe suggests strongly that the fans that always run full speed are not getting any PWM signal from Pin #4. So you may have poor connections at either the mobo header end or the Splitter output that has the fan plugged into it. Try simply unplugging at each junction and re-plugging several times, in case that cleans off contacts and gets them working.

You don't understand fan signal lines. This will concentrate on 4-pin fans only. On the fan cable end there's a connector with 4 holes, and two ridges down one side. Those ridges "surround" Pins 1 to 3, and Pin #4 is outside them. Their functions:

Pin #1 is Ground
Pin #2 is +12 VDC power supply - always 12 V for a 4-pin header using PWM Mode
Pin #3 is fan speed signal generated in the fan and going back to the mobo fan header
Pin #4 is the PWM signal.

A 4-pin fan has a special chip inside that uses the PWM signal to modify the flow of current from the +12 VDC supply (Pin #2) through the windings to change speed. With NO PWM signal, the fan will run at full speed. The mobo header does NOT use the speed signal coming back to it via Pin #3 to control fan speed. But it will display that for you, and will monitor it for NO speed indicating fan FAILURE, and send you a warning.

A mobo fan header can deal with the speed signal coming to it from only ONE fan. So any Splitter or Hub will send back the speed of only ONE of its fans and ignore all the others. The very simple way to do this is to ensure that the Splitter has only ONE output (male with pins) with all 4 pins, and to NOT include Pin #3 in other outputs. So those outputs with missing PIN #3 have nothing to do with your problem. Note that this also means that, when you use a Splitter or Hub, the mobo header with the cable to the Splitter or Hub will only be able to show you ONE fan's speed, and will never "see" or display any others of that group. nor be able to monitor any of those "others" for failure.
 

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