4x 3-pin Fans to 1x 4-Pin Header on ASUS Prime B350M-A mATX MOBO

Hi,
To avoid all the hassle, I suggest a fan controller. Something like https://www.newegg.com/Product/Product.aspx?Item=N82E16811992013
A bit expensive, but... a better solution on long term.

You're welcome, and thanks for Best Solution.

I have exactly the same case, but with Ryzen 7 1700. So how has the Phanteks PWM Hub PH-PWHUB_01 been working for you? I like the idea that it supports both 3 or 4 pin fans, as I would prefer not to drop the 3 fans that came with the Air 240 and having to replace with PWM fans, UNLESS there is a really good reason to do so.

I hope TSpec87 replies with actual experience of use. I will offer a couple of comments regarding what MIGHT be factors for you when dealing with a mix of 3-pin and 4-pin fans.

As a general rule, 4-pin fans are a slightly better design. They can be started up at slower speeds, and can be run at lower minimum speeds without risk of stalling. The start-up speed often is not an issue, though. Many mobos always start all their fans at full speed for a few seconds, then slow them down as the automatic control system gets temperature readings from sensors. So, replacing them with 3-pin fans may not be the best path.

Technically, 4-pin fans really ought to be powered and controlled in PWM Mode. However, you cannot mix 3-pin and 4-pin fans together using that control Mode, because 3-pin fans cannot be controlled that way. If you go the route of using the Phanteks PWM Hub, all the fans ARE controlled using Voltage Control Mode. Now, technically that is not ideal for 4-pin fans. Doing that basically disables the two advantages of slow start speed and lower minimum run speed, but those may not matter to you. Some people and fan makers suggest that supplying a PWM fan with varying reduced voltages and no PWM signal (that is, under Voltage Control Mode) MAY reduce the lifetime of the PWM fan. I have not read any specific figures on the magnitude of this impact.

IF those possible downsides of using 4-pin fans under Voltage Control Mode are a concern for you, of course one solution would be to replace them with 3-pin fans, at some expense. But assuming you have OP's situation - mix of fan types and only one mobo SYS_FAN header that really does use PWM Mode - there is another arrangement. You buy and use a second Hub, but make this one a simple type that is ideal for 4-pin fans systems only. Here's one example:

https://www.newegg.com/Product/Product.aspx?Item=N82E16882422018&cm_re=fan_hub-_-82-422-018-_-Product

Note that this unit must connect BOTH to a mobo 4-pin fan header using PWM Mode and to a PSU 4-pin Molex power output. Using this you can plug it into your only mobo fan header, then plug all your 4-pin fans into it to be controlled "properly". But then you also plug the fan connector coming from your Phanteks Hub into one of the ports of this Hub. (Of course, the Phanteks still needs to be connected to a PSU power source also.) Then the Phanteks Hub gets the PWM signal it needs from the other Hub, and it can control your 3-pin fans because of its own internal conversion of control Mode. In this way you can power and control many fans from a single 4-pin mobo header that is using PWM Mode, and still have each sub-group (3-pin and 4-pin) controlled using their "ideal" respective Modes.

I understand the difference between the 3 and 4 wire fans and PWM vs power. My issue was that I was looking for some method to speed regulate the 3 x 3wire fans I have with the 1 x 4pin fan header on motherboard. So, if I understand correctly, it looks like the Phanteks PH-PWHUB_01 PWM Fan Hub would be able to correctly control my 3wire fans using control input from 4pin PWM motherboard fan header and power from psu?
I would really have expected ASUS (or any other microATX motherboard vendor) to have provided one with some solution other than "make your own plan" when one was used to having case fan and optional headers on motherboard.

I agree with you a bit on the problems of mis-match between cases with 3-pin fans included and pre-installed, and mobos with limited fan headers. There are two "reasons" I think.

It appears that almost all fans that come included with cases are of the 3-pin design. I'm sure this is a cost thing, odd though it may seem. Comparing very comparable fans of 3- and 4-pin designs, the 3-pin typically is cheaper by several dollars at the retail level. So by supplying those, a case maker can keep the selling price down a few dollars per fan ($10 per case?) and make the case more attractive to buyers. The fact is that both fan types CAN deliver comparable performance. The main advantages of the newer 4-pin design pertain to low-speed operation, and that may be a small factor for case ventilation. People with few fans don't want them to run slow, and aficionados with many fans for super cooling usually don't care about having them run slow and quiet.

So, how can mobo makers provide for the possible use of both fan types? Lately they all use 4-pin headers on the mobo so nobody will worry. But electrically, how to arrange them since the two fan types require different control methods? Some don't provide for that - you get either PWM Mode for 4-pin fans OR Voltage Control Mode (DC Mode) for 3-pin fans, and you have to fit your fans to that. This means you need to understand fans a bit and plan for it as you buy. Some provide both Mode options and let you chose in BIOS Setup. Some provide both options AND a feature on each fan header that automatically detects what type of fan is connected and adjusts its Mode accordingly. Both these designs are more complex and expensive, but do the task well. Some mobos use a small trick. You see, the PWM fan design has some backwards compatibility features, and one of those is that, when plugged into a 3-pin fan header that uses only Voltage Control Mode with no PWM signal supplied, the fan still IS speed controlled. It's not ideal, but it does work well and leaves the user worry-free. So the mobo maker's "trick" is that the 4-pin header actually works only as a 3-pin header, and both fan types appear to be working just fine with no effort by the user. This design has one problem that is not obvious - since it provides no PWM signal, it can NOT be used with 4-pin fan HUBS, because they require that signal.

Then comes the consideration of how many? And that gets linked to fan type. Virtually all mobo fan headers are limited to 1.0 amps total current draw for all fans connected to that header. (There are now some mobos with one special 3 amp header, although their use with many 3-pin fans seems to have limits I don't quite understand.) So you can use Splitters to connect more than one fan to each header, but the mobo makers leave it your responsibility to ensure you conform to that limit, so you have to do a bit of work. There are also different devices called Hubs that avoid the power limit of the header by getting all fan power directly from a high-amp source at the PSU. The dilemma there is that such devices MUST have a PWM signal from the mobo header (and some headers cannot provide that) and most (excepting a few) Hubs work only with 4-pin fans. So for the most part, if you are using 3-pin fans you can only use a Splitter, and that means you are limited to the 1 amp available from one header. One exception I know about this latter is the Phanteks PWM Hub. It does need a PWM signal from the mobo header, but it "converts" to using 3-pin Voltage Control Mode for all its fans; thus it can control both 3- and 4-pin fans (the latter because of that backwards compatibility feature).

Another factor in the how many? discussion is mobo type, The users of microATX boards are aiming for smaller system size and thus expect to have fewer resources for add-in boards and features, and less processing power than many full-size ATX boards can deliver. This means that the likely system power use and heat generation is lower; hence the number of fan headers (and fans) can be fewer. Users of microATX boards who want many fans are left to their own planning process to deal with that matter.

ASUS and other mobo makers have to deal with the market reality that both fan designs are used widely; further, case makers all seem to go for the low-cost 3-pin option. So the best the mobo makers can do is provide for both possibilities and let you adjust according to what else you bought. But that does mean you have to learn a bit about these details and know how to make that adjustment. It also means the extra cost of the more complex fan header design is built into the mobo price, rather than into the case price. The user pays one way or the other - "there is no free lunch".