[SOLVED] Molex Fan Splitter Questions - Please help :(

Jul 12, 2020
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I've been researching literally for hours regarding this. I have a thermaltake core v1 case and it has a preinstalled 200mm front fan. I will also get two Noctua NF-R8 redux-1800 PWN 80mm fans for the rear.

My motherboard (Gigabyte b450i aorus pro wifi MITX) only has two fan headers however. One for the CPU cooler and one for the case fan. I've opted with getting a splitter, but this is where my anxiety seeps in :chaudar:

This is the splitter in question: https://www.overclockers.co.uk/ek-water-blocks-ek-cable-splitter-4-fan-pwm-extended-wc-9cq-ek.html

It has a molex connector and one for the motherboard fan header. The motherboard can take 2A per header and the two Noctua fans are 0.06A each. I have no idea about the front 200mm fan, I can't find any information about it. I'm planning on leaving the CPU header for it's own dedicated cooler, and putting the splitter into the system fan header for to run three fans off it. Will it fry anything? Does the molex going into the PSU ensure that nothing will be fried because of the extra power? Also, do I need to use all 4 of the ports on the splitter, or can I just use 3?

Thank you!
 
Jul 12, 2020
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I have other concerns though. Will it be safe? Because I don't know the rating for the front 200mm fan. That's why I'd rather get the molex one:

https://www.overclockers.co.uk/ek-water-blocks-ek-cable-splitter-4-fan-pwm-extended-wc-9cq-ek.html

Will it fry anything? Does the molex going into the PSU ensure that nothing will be fried because of the extra power? Also, do I need to use all 4 of the ports on the splitter, or can I just use 3?

Thank you!
 

1405

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Aug 26, 2012
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I'd go with the OP's choice. Most motherboard headers will be maxed out at 2 fans if you take into consideration starting current spike. The Molex connector splitter will feed the fan motors' loads directly from the PSU, eliminating the load the motherboard header has to provide. It will only use the PWM control from the header to modulate RPM.
 
Reactions: skidmark2007
Jul 12, 2020
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I'd go with the OP's choice. Most motherboard headers will be maxed out at 2 fans if you take into consideration starting current spike. The Molex connector splitter will feed the fan motors' loads directly from the PSU, eliminating the load the motherboard header has to provide. It will only use the PWM control from the header to modulate RPM.
Is the "OP" the four way splitter I listed in my question? Is it ok to just use 3 instead of all 4?

Thank you!
 

Paperdoc

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OP, you and SO MANY others have been confused by the rampant misuse by sellers of the terms "Splitter" and "Hub". They seem to use them as descriptions of the appearance of the device, with "Splitter" used to name groups of wires and cables, and "Hub" used for a box with ports. I prefer to name them according to their ELECTRICAL FUNCTION.

To me, a SPLITTER is a simple device that simply connects all its fans in parallel to the host header. The only power available in that case is what comes from the header (usually limited to 1.0 A, sometime more) and that is SPLIT among all the fans. It has NO connection to the PSU. Such a device may look like a group of cable arms with one female connector and two or more male output arms, or like a small circuit board with male pins forming headers, or even a small box with ports in its sides. A Splitter may be a 3-pin or 4-pin device, and both types can be used with 3-pin fans because of the design of the 4-pin system. (But see comment below on speed control.)

A HUB is a different device. It has one input "arm" that goes to a mobo host header, two or more outputs with male pins, plus a third type of connection "arm" that must go the a SATA or 4-pin Molex power output from the PSU. The Hub shares to all its fans the PWM signal it MUST receive from Pin #4 of the host header, but that is the only host header signal it sends to its fans. The Power and Ground connections to all its fans come from the PSU, which has a much higher max current limit than any mobo header. So when you use a HUB, you do NOT risk overloading the mobo host header. With one or two exceptions, all HUBS are solely for 4-pin fan systems. The require the PWM signal from the mobo, and the can only distribute that to their fans. So the FANS used with a Hub must be of the 4-pin type able to use the PWM control signal. If you plug a 3-pin fan into the output of a Hub, it will behave just as if you had plugged it into a mobo 4-pin PWM header - it will always run full speed. A HUB may look like a collection of cable "arms", or like a small circuit board, or a box with ports, just as a Splitter might. What makes it unique is the presence of that third "arm" type that must plug into a PSU output for power to the fans. A Hub is ALWAYS a 4-pin device, so any 3-pin device must be a Splitter.

The only way to control the SPEED of 3-pin fans is to use the older Voltage Control Mode (aka DC Mode) in the mobo fan header configuration, and ONLY a Splitter can re-distribute all of those signals. Thus connecting several 3-pin fans to a single header by using a Splitter is limited to the max current spec of the header, typically 1.0 A. As it happens, the new 4-pin fans were designed to be able to work with speed controlled when connected to a 3-pin fan header, so you CAN use them with a Splitter and a header using that older Mode.

I will note here that there is a new Phanteks product that IS a HUB but DOES also operate properly with both 3-pin and 4-pin fans and headers thanks to a very unique design.

A general note that applies to both Splitters and Hubs. Any mobo can accept and handle the speed signal sent back to it from ONE fan only. So any proper Splitter or Hub will send back to its host header the speed from only ONE of its output ports, and almost always that port is marked clearly. The speeds of all of the other fans on the device will simply be ignored and never "seen" by anything. This has NO impact on ability to control fan speeds since the mobo does NOT use the speed signal to control the fan. However, a mobo fan header also monitors it speed signal for fan FAILURE, which is what it assumes if it get NO speed signal. So when using a Splitter or Hub, all those "other" fans cannot be monitored for failure, and YOU need to check from time to time that they are still working. But DO ensure that one fan IS plugged into the special marked output.

After all that, OP, the item you linked to first is what I call a HUB. It gets all fan power from the PSU, it gets the PWM signal only from the mobo header, and it distributes those on four output "arms". As long as all your fans are of the 4-pin type, it will do the job for quite well, and it will NOT overload your mobo header. The 3-ouput device linked by Zerk2012 above is a SPLITTER that gets all its power solely from the mobo header, and hence is limited to that header's max current. It could be used with any mix of 3- or 4-pin fans, BUT if any of the fans are 3-pin, then the header must be configured to use Voltage Control Mode. From the info above it appears VERY likely that the total max load of the fans you cite will NOT exceed the 2 A limit you cite (probably not even 1 A), so you could use either device.
 

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