[SOLVED] Using a pwm fan hub to split power, no attached motherboard. I need help, please!

Sep 22, 2021
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Okay so I have been trying to power 9 120mm 5v fans (these fans are designed for use with a raspberry pi gpio pin connection; furthermore, it has LEDs in it; the fan is designed such that the LEDs and fan are separately powered; meaning two 5v wires and two ground wires to plug in) I am using a 12 port pwm fan hub chassis plugged to a PSU to power them. This hub has 10 fan ports (one for cpu fan, and 9 non-controlled ports for fans; the 9 will only be able to mimic speed control of the cpu fan port.

Each of these 10 ports are 4 pin mini molex ports designed for 3 and 4 pin fan connections), the other port is for 4 pin mini molex and only labeled pwm (meant to plug to the motherboard). The last port is 4 pin molex meant to plug to the power supply. I have the fan hub powered to a PSU just fine, I can easily power the LEDs off of the 5v and ground of the mini molex on input pin 1 and 2 (with the 5v and ground wires for the LEDs) to the fan hub. I can easily power the fan with the pwm and speed data input pins 3 and 4 on the mini molex of the fan hub, using the 5v and ground wires for the fan motor, ( for each of the 9 fans).

THE PROBLEM: the fans will only pulse on and off, I NEED continuous spinning of the fans (I have temporarily been able to connect the 5v wire and ground wire, that controls the fan motor, to the GPIO pins of the raspberry pi and it works just fine and continuously, while still powering the LEDs from the fan hub ports v and ground inputs. I do NOT want to power the fans or LEDs off of the gpio pins of the raspberry pi (I need all of these pins for i2c and spi interfaces, also I do not want be be powering anymore than that on the raspberry pi). I am also trying to bypass the need of using a motherboard connected to the fan hub.

My understanding is that I just lose the ability to control the speed based on temp readings from the cpu (I don’t need this as the fans will run as 100% all the time; it is only like 600 rpm fans). I have everything running with the exception that the fans will only pulse on and off when plugged to the fan hub, this is what I need help with (all WITHOUT connecting to a motherboard).

My initial thought is to ground out the pwm and speed data pins on the “pwm labeled” port that goes to the motherboard (though not able to test at the moment because I am at work), would this do anything?

My next thought was to figure a way to program a pi zero or rpi4 as a “fill in motherboard”, just to have the circuit completed. I am sure there is also some way to actually control the fans from a pi as well, but this is far beyond my own knowledge to build a program to do this (I am also very lazy and want a simple quick solution).

Lastly, please understand I am a noob and new to pc hardware and software related projects (though I am a learning hobbyist); that being said, if something I said in this post sounds silly (ie, calling something the wrong name, etc.), then it probably is. For this, I apologize and hope that I have reached those more knowledgeable than me, such that you are able to piece together what I am talking about, enough to help me figure this out. I will link the fan hub and the fans that I am using. I will try to post pictures of how it looks once I have stimulated discussion (and have the time off; which will be much later today, just getting off a 16 hour shift). Please help me?!

fans:
GeeekPi New Raspberry Pi Cluster Case, Raspberry Pi Rack Case Stackable Case with Cooling Fan 120mm RGB LED 5V Fan for Raspberry Pi 4B/3B+/3B/2B/B+ and Jetson Nano (12-Layers) https://www.amazon.com/dp/B08FH3V6GV/ref=cm_sw_r_cp_api_glt_fabc_FA8FN4YC84HQJPJDDXTW

fan hub:
Electop PC Chassis Fan Hub CPU Cooling HUB 10 Port 12V 4 Pin Fan PWM Hub Molex Controller https://www.amazon.com/dp/B071KNT7F...abc_431FPDGK2T9F3W9XEAA6?_encoding=UTF8&psc=1
 
Solution
I have everything running with the exception that the fans will only pulse on and off when plugged to the fan hub, this is what I need help with (all WITHOUT connecting to a motherboard).

It seems you fail to see how PWM actually works.

PWM fans/hub, have 4 pins:
pin #1 - +12V
pin #2 - ground
pin #3 - sense (RPM feed back to the MoBo)
pin #4 - PWM (PWM control for 4-pin fans)

PWM needs constant full power, +12V to the fans/hub, where the PWM signal is used to control the speed of the fan.

Though, the fans you linked, are 2-pin 5V fans, and to keep them running, all you need to do, is connect them to +5V power source. NOT connecting them to +12V PWM fan hub. Since at current moment, you're trying to feed +12V into +5V fans...

Aeacus

Titan
Ambassador
I have everything running with the exception that the fans will only pulse on and off when plugged to the fan hub, this is what I need help with (all WITHOUT connecting to a motherboard).

It seems you fail to see how PWM actually works.

PWM fans/hub, have 4 pins:
pin #1 - +12V
pin #2 - ground
pin #3 - sense (RPM feed back to the MoBo)
pin #4 - PWM (PWM control for 4-pin fans)

PWM needs constant full power, +12V to the fans/hub, where the PWM signal is used to control the speed of the fan.

Though, the fans you linked, are 2-pin 5V fans, and to keep them running, all you need to do, is connect them to +5V power source. NOT connecting them to +12V PWM fan hub. Since at current moment, you're trying to feed +12V into +5V fans, which doesn't work. Either the fan won't spin, or you fry the fan motor.

To get your fans going, you need to reduce the +12V from PSU, to +5V, that fans operate at. There are several such fan adapters out there, and you can even make it on your own. Just take the molex connector from PSU and split it, only using the 5V power cables + grounds. Or buy the molex to 12V/5V fan adapter.

E.g this one:

1Pcs-4Pin-to-3Pin-Fan-Power-Cable-Adapter-12v-2-5v-2-for-Computer-Cooling-Fan.jpg


amazon: https://www.amazon.com/Computer-Cooling-Cables-Adapter-Connector/dp/B07SNCMQ2C
 
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Solution
Sep 22, 2021
7
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10
It seems you fail to see how PWM actually works.

PWM fans/hub, have 4 pins:
pin #1 - +12V
pin #2 - ground
pin #3 - sense (RPM feed back to the MoBo)
pin #4 - PWM (PWM control for 4-pin fans)

PWM needs constant full power, +12V to the fans/hub, where the PWM signal is used to control the speed of the fan.

Though, the fans you linked, are 2-pin 5V fans, and to keep them running, all you need to do, is connect them to +5V power source. NOT connecting them to +12V PWM fan hub. Since at current moment, you're trying to feed +12V into +5V fans, which doesn't work. Either the fan won't spin, or you fry the fan motor.

To get your fans going, you need to reduce the +12V from PSU, to +5V, that fans operate at. There are several such fan adapters out there, and you can even make it on your own. Just take the molex connector from PSU and split it, only using the 5V power cables + grounds. Or buy the molex to 12V/5V fan adapter.

E.g this one:

1Pcs-4Pin-to-3Pin-Fan-Power-Cable-Adapter-12v-2-5v-2-for-Computer-Cooling-Fan.jpg


amazon: https://www.amazon.com/Computer-Cooling-Cables-Adapter-Connector/dp/B07SNCMQ2C

Thanks very much for the insight! You probably right, I didn’t quite fully understand how it works. I was assuming there was a way to convert it after the fan hub. I think I can leave the hub in place for the LEDs, they seem to be fine. But even if I use the molex to 5v that you mention, I would still have need nine 5v sources. I only have 3 miles plugs on my PSU (one powers the fan hub and splits to 9 sources for the LEDs). I would need a molex to 5v that is split 5 times for each plug. Is this possible??
 
Sep 22, 2021
7
0
10
Thanks very much for the insight! You probably right, I didn’t quite fully understand how it works. I was assuming there was a way to convert it after the fan hub. I think I can leave the hub in place for the LEDs, they seem to be fine. But even if I use the molex to 5v that you mention, I would still have need nine 5v sources. I only have 3 miles plugs on my PSU (one powers the fan hub and splits to 9 sources for the LEDs). I would need a molex to 5v that is split 5 times for each plug. Is this possible??
Molex** not miles
 

Aeacus

Titan
Ambassador
My question would be, why do you need 9 fans in the first place? It looks way overkill to me for a single build/system.

For example, my Skylake build (full specs with pics in my sig), is in the full-tower ATX case and i have 7 case fans, where 6 of them are 140mm and last one is 120mm.

I would need a molex to 5v that is split 5 times for each plug. Is this possible??

Possible? Yes.
Especially when you have 5-way splitter, like this one;
amazon: https://www.amazon.de/dp/B08GBLR4Q5

Though, do note that the linked splitter is 12V and to make it into 5V, you need to rewire the cable inside the molex connector, from 12V to 5V.

With this 5-way splitter, you'd essentially need 2 of them, to power all 9 (or 10) fans. And you can use up two molex connectors, or get molex splitter to hook them up all to single molex connector;
amazon: https://www.amazon.de/dp/B07TWFWQDC/

Also, fans doesn't consume much power and your PSU should be able to handle 9 fans on 5V rail. But just in case, what Amperage rating the fans are? And what is your PSU make and model (or part number). Since with that info, i can calculate how much power 9 fans consume and look up how much your PSU 5V rail is rated for (in terms of Watts).
 

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