3 pin case fan question

[dpeel]

I have a Asus Prime X470-Pro Motherboard and a Mid Tower ATX Case and plan to add 4 120MM 3 pin case fans for air flow through the case.....2 in the front pulling air in and 2 in the top pulling air out. The case already had 1 120MM fan in the back top so there will be a total of 5 120MM fans circulating air through the case. There are 3 4pin fan headers on the motherboard. I am wondering what the best way would be to power these fans. I know you can buy a 4 pin to 3 pin connector that can be connected to one of the 4 pin connections on the power supply but is that the best way?

 

[Darkbreeze]

Not really. I'd recommend something like the Grid+ v2 or v3. Most boards will only run 3 pin voltage controlled fans at full speed when run off their PWM headers, not particularly desirable.

This will do the trick nicely. I have the v2 version and have never had any issues with the operation or controls. Easily tailor you fan curves, for each fan if you wish, using the CAM software. You can configure the fans to run all the way down to 20% speed at low temps and increase to full speed at any temp you wish with curve points that can be configured at about seven points along the way from high to low.

Either version will work fine. There are less expensive options as well, but they will lack the level of configuration and control you get with the Grid+. Generally speaking, the fan curve controls are better than what I've seen so far in pretty much any motherboard bios fan controls.

https://www.amazon.com/Nzxt-Digital-Controller-connector-AC-GRDP2-M1/dp/B0156YBCKG

https://www.nzxt.com/products/grid-plus-v3

 

[dpeel]

I appreciate your response. I see now that you can connect the 3 pin fans to these motherboard headers but I guess I wouldn't be able to control the speed in the motherboard bios since they are 3 pin instead of 4 pin fans. I really don't want to buy 4 pin fans and guess I'll just run them at full speed. That's pretty much what I've done in the past and haven't had a problem with noise.

 

[Darkbreeze]

Actually, you can do this for fairly cheap, if you feel like you don't want to make the larger investment. I wouldn't have thought it was worth it either, but after using the Grid+ for a few years now, I'd never go back to motherboard controls myself unless they advance sufficiently to allow for the same level of individual location control that you get with the Grid+.

Being able to choose individual presets for each fan is great and all, and even set a few thermal points for a custom curve on motherboard bios fan controls, but being able to set MANY thermal points to tailor the fan speed at seven or more temperatures is just hard to ignore.

Still, this would work for you as well and is fairly inexpensive.

https://www.amazon.com/SilverStone-System-Cables-Black-CPF04/dp/B00VNW556I/ref=sr_1_3?ie=UTF8&qid=1539103650&sr=8-3&keywords=pwm+fan+hub

 

[Paperdoc]

There's a really simple solution and all you need to buy is a couple of simple fan SPLITTERS, like this

https://www.newegg.com/Product/Product.aspx?Item=N82E16812423168&cm_re=Coboc_fan_splitter-_-12-423-168-_-Product

or this

https://www.newegg.com/Product/Product.aspx?Item=N82E16812423161&cm_re=Coboc_fan_splitter-_-12-423-161-_-Product

That latter one is a 4-pin unit, but it WILL work just fine with your 3-pin fans.

Your mobo has three CHA_FAN headers, so I suspect you already have your one rear case fan plugged into one of them, leaving two unused. Most importantly, each of those headers can be configured in BIOS Setup to work properly with either 3-pin or 4-pin fans. I suggest you use the two splitters (one on each of the unused headers) to connect pairs (front pair / top pair) to those headers. Then in BIOS Setup (See manual p. 3-7) for each of the two headers that power the 3-pin fans, set it to use "DC Mode" at upper right. IF there is a choice about which temperature sensor to use for each header, I recommend the common Motherboard sensor, NOT the CPU sensor or other special mobo component one. Remember to SAVE and EXIT to save these settings. Then the mobo can power AND control the speeds of all your case fans according to the temperature if the motherboard.

 

[Paperdoc]

(Duplicate post deleted.)

 

[Darkbreeze]

Maybe. I've seen some of these configurations on ASUS boards with both PWM and DC controls still only allow full speed operation on the 4 pin headers when using 3 pin fans.

 

[dpeel]

Thanks for your responses. I went to Micro Center this morning and bought a splitter that will connect 3 of the 120mm 3 pin fans from 1 motherboard headers. That should give me enough connections for all fans. I have decided that I will run them all at 100% and not worry about it.

 

[Darkbreeze]

The noise level from a single fan running full speed would drive me batshit crazy. I can't imagine having three doing it. But it you're ok with it, that's all that matters. Good luck to you man.

 

[Paperdoc]

That will work, but for NO extra money you CAN have the speeds of all fans controlled by your mobo's CHA_FAN headers. You merely need to configure each of them to use DC Mode rather than PWM Mode.

 

[Darkbreeze]

AND, I would try ^^^^ THAT first. I can tell you for certain that DC mode will NOT work with my Hero VIII and my 3 pin Aerocool DS 140 3 pin fans, except on full speed operation. I've seen this on a couple of other ASUS boards as well that have PWM or DC mode in the Q-fan controls, but I've also seen them work on a few implementations as well. I can't say it will or will not. Only that I've seen it go both ways. On my board and two others I've worked on, it would not work that way, but it's certainly worth trying for no cost, just a quick trip into your bios settings and five minutes of your time.

 

[dpeel]

Since all the 5 120mm fans will be connected to the 3 fan headers on my motherboard, I will see if I can adjust fan speed in the bios. I was under the impression that I wouldn't be able to as I am not connecting using a 4 pin fans.

 

[Darkbreeze]

IF it works, you will have to make sure you ONLY use the headers labeled CHA_FAN for chassis fans, as I'm pretty sure those are the only ones that have the pin arrangement in such a way that they can be BOTH PWM and DC controlled. I'm still not entirely certain how they manage to make PWM fans work with two different pin configurations, and a DC mode, but obviously they do.

I just think that some of these implementations only allow for DC control with 4 pin fans, so you will have to simply make the changes and check the operation using your 3 pin versions. I may even double check mine just to be sure I'm not talking out my behind.

 

[Paperdoc]

Many (but certainly not all) mobo fan header that can be set to use EITHER Voltage Control Mode (aka DC Mode) or PWM Mode. When set to PWM Mode they can ONLY control the speed of 4-pin fans because that depends on the fans themselves having the necessary chip to use the PWM signal for control. However, IF the header is set to use DC Mode, then what it SHOULD be doing is acting exactly like a 3-pin fan header and ignoring the PWM signal line (Pin #4) entirely. That is, it sends out on the power line (Pin #2) a voltage that VARIES from +12 VDC down to about +5 VDC to change the fan speed. (A voltage under 5 VDC may cause the fan to stall and not re-start until the supply voltage is raised.) This is the ONLY way to control an older 3-pin fan. But 4-pin fans have been designed with a backwards compatibility feature. IF one of those is connected to a true 3-pin fan header (or a 4-pin header using DC Mode), it gets NO PWM signal so it cannot apply that to the incoming power supply. BUT that supply is not a fixed +12 VDC - it is varying per the 3-pin fan system design, so the motor speed DOES change as that voltage changes. Effectively that 4-pin fan IS speed-controlled by using Voltage Control Mode, although technically that is not quite as good as using the "correct" PWM Mode for that fan.

 

[Darkbreeze]

So, I checked again. On my Hero VIII headers my four pin Noctua PWM fans will work, raising and lowering speeds in direct relation to temperature, with both settings PWM and DC. My 3 pin Aerocool fans, will only run at full speed when connected to those same headers even when DC mode is enabled. They work perfectly fine with my Grid+ v2 voltage controlled PWM to 3 pin header unit however.

I don't know what to say, it is what it is. As I said, I've seen some of these with the PWM or DC option that do work fine though. I would certainly try it before buying additional hardware, HOWEVER, it still remains that the fine tuning control capability of the Grid+ units is much better than what I can do with my Qfan controls that only allow 3 different thermal points for tailoring the fan curve.

 

[Paperdoc]

Now that's very interesting, darkbreeze. I have often suspected that a few mobo makers take a "short cut" the other way. That is, the represent their fan headers as "automatic", and thus able to detect which fan type is attached and adjust themselves accordingly. Certainly that could be done. BUT it also is possible to "fake" that by making that header only operate in the older Voltage Control Mode and depending on the backwards compatibility feature of 4-pin fans to appear to benefit from such a design. It does get exposed, though, if a user tries to use a 4-pin fan HUB on that header, and it fails because there really is no PWM signal provided from Pin #4.

Your experience is just the opposite. The board claims to let you specify either Mode, but appears only to work in PWM Mode.

 

[Darkbreeze]

What's really weird is that both PWM and DC modes work fine with my 4 pin PWM Noctua fans. But DC mode doesn't work with my 3 pin Aerocool fans. Yet those same fans work fine on a Grid+ that uses voltage controls and they work fine on the 3 pin DC headers on one of my old ASUS 990fx boards.