Question Molex plug powered fan control?

Jul 10, 2020
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So I acquired a PCI exhaust fan for my home media server build. It only has two wires, (red and black) on it that use a molex 4 pin style plug. I was wondering if there is a way to use a controller that would allow the fan to turn on and off as needed rather than run constantly. I don't think that the speed can be controlled since it's only a two wire but I wasn't sure if there is some kind of controller that can be used to turn it on and off at a set certain temperature. I was also wondering if it could be "piggy backed" on another fan circuit that only supplied power to a fan when needed.

This might be a stupid question to ask or probably isn't possible but I figured I would ask.


This is the PCI fan I have: https://www.amazon.com/gp/product/B0000510SS/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1





Thanks for your time and help!
 
I don't believe there is, to rephrase what you want:
A device that turns off power to the fan when the temperature isn't that high for it to be on.

Something like this would require these:
  • Power-in port: Molex / SATA power
  • Power-out port: Molex -> PCIe fan
  • fan header to connect cable to motherboard for temp sensor reading and configuration.
But all this would require software on board or third party that controls the board on when power should be turned on and off (third-party software would allow more configurability). This kind of thing exists on normal fan controllers since the fans require simple fan headers but since the connector for that PCIe fan is molex, makes it all the more tricky to find. If it exists....
 
Reactions: koslaw
Jul 10, 2020
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Yeah that's what I figured but wasn't sure. I saw some mods that can be done by switching the wires around on the plug to run the fan at slower speeds. I might try doing that instead since it's a bit loud when running at full bore. I think the pins can be switched to run it off either a 7 volt or 5 volt so it's not running as fast causing more fan noise.
 
Yeah that's what I figured but wasn't sure. I saw some mods that can be done by switching the wires around on the plug to run the fan at slower speeds. I might try doing that instead since it's a bit loud when running at full bore. I think the pins can be switched to run it off either a 7 volt or 5 volt so it's not running as fast causing more fan noise.
Could also just try this, and plug it into a normal fan header.
https://www.newegg.com/p/N82E16812198160?item=N82E16812198160&source=region&nm_mc=knc-googleadwords-pc&cm_mmc=knc-googleadwords-pc-_-pla-_-cables+-+internal+power+cables-_-N82E16812198160&gclid=Cj0KCQjw3duCBhCAARIsAJeFyPWxv0cB0nbIOATanrCl_LQurdE9jpiwZW2axU6xY0CPu2jjmh1Czb8aAnoMEALw_wcB&gclsrc=aw.ds
 

Paperdoc

Glorious
Ambassador
Your asked how "to turn it on and off at a set certain temperature". There are ways, but first you need to know:
Temperature of what (thing whose temp you measure)?
What is the "proper" target temp?

ONE way to do this would be to use the automatic fan speed control system already on your mobo. This CAN be rigged to control the speed of this fan, not just turn on and off. But it will need a bit of custom mod work by you, and an unused fan header you can dedicate to this fan. ALSO, a mobo fan header normally can be set to use a common temperature sensor on the mobo placed in a spot the mobo maker considers important for cooling generally. This does NOT allow you to base the fan's speed on the temperature of a particular component. (There are a FEW mobos that come with an extra temp probe you can place where you like and connect to a special mobo header, but we do not know if your mobo has this.)

If that would be an acceptable way to control this fan, the mod you need is easy. That fan is a common 12 VDC fan for which you CAN control the speed simply by changing the VOLTAGE supplied to it, just like all the older 3-pin fans. A standard 3-pin fan comes with THREE wires to it: Black for Ground, Red for the + VDC supply, and Yellow to feed a fan speed signal back to the mobo. Your fan simply is missing the Yellow, and that does not matter. You need a standard 3-pin fan female connector - scavenge one from an old 3-pin fan if you have one, or get from a used computer parts shop. Cut it off the old fan's wires with some of the wire still in the connector. Snip off the Molex on the end your fan's wires. Splice Black Black, Red to Red, and tape up the Yellow so it does not short out anywhere. You have just converted your new fan to an almost-standard 3-pin fan. It can be powered from AND have its speed controlled by a standard mobo fan header. Almost all headers now have 4 pins, BUT in BIOS Setup for each header you have a configuration option to set its MODE, which is the type of electrical signals sent out. For this 3-pin fan, the header used MUST be set to Voltage Control Mode (aka DC Mode). IF you want it to be controlled exactly like some other 3-pin case ventilation fan in your system, you can connect this one with others to a header using a Splitter. But if you want this one to be controlled to a different temperature setting, you will need to give it its own header and set up the controls as you want. You may have a choice of which temp sensor in the mobo to use.

If you want details of how to set up headers for this, tell us your mobo maker and exact model so we can look up its manual and advise.

By the way, the adapter etc. linked above will not do what you ask. The simple adapter will feed power from a Molex PSU output into a standard fan's FEMALE connector, which you don't have. It can NOT connect from a mobo MALE fan header to your fan's Molex. The rear-slot control knob item is a MANUAL speed adjuster (just a resistor you can change, not any automatic switch or control). It has power input from a PSU via a Molex, and outputs to THREE fans that have standard female fan connectors on them - yours does not (yet).

Lastly, an option closer to what you asked. You CAN buy third-party Fan Controller modules that mount in the front of your case (in a 5¼" slot often) and give you some means to control the speed of a standard 3-pin fan. (Yours can be made to work this way with the mod above.) The most common type allow you to exercise MANUAL control of the fans. A fancier version comes with temperature probes you can mount where you like, and can display those temps for you so YOU can manually set fan speeds. There may be a few models even fancier (and more expensive) still available that actually use those temp probes to do automatic speed control similar to what your mobo can do. The difference would be that this last kind of fan Controller can use its own temp probes in places you choose, rather than using the mobo temp sensor already in a fixed location.
 
Reactions: koslaw
Jul 10, 2020
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Thanks everyone for the great responses. I will probably mod the fan plug so it can plug into the mobo fan header. I do have an extra one but I will need to see where it's temp sensor is located. Mostly at this point I don't want the fan to be running at full speed all the time as it can be a little noisy.
 

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