Question 3-pin fans on 4-pin PWM controlled adapter

Oct 13, 2019
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Hi guys!
I'm about to upgrade some parts on my PC, especially the cooling/noise reduction.
I'm gonna buy a Fractal Define S, which has 2x 140mm 3-pin fans, I also have 2x 140mm 3-pin fans AND 4x 140mm 4-pin PWM fans laying around.
So there are 4x 3-pin and 4x 4-pin fans. Since no MoBo has so many connectors I bought a Lamptron SP105 adapter. It sais in its description that it can drive 3-pin fans, kinda obvious I think. But what isn't stated anywhere is if it can also controll the speed of said 3-pin fans. In my understanding, that is not so obvious. 3-pin fans are controlled via voltage altering, and since the adapter is SATA/MOLEX-powered, I assume that the VCC on the 4-pin headers of the adapter are fixed to 12V, that of course would mean that the 3-pin fans would run at 100%.
If the adapter is designed a bit smartish, it would alter the VCC according to the PWM-input from the MoBo, but on the pictures I can't find any kind of IC or such that could be accounted for that...

Has anyone an educated guess or first-hand experience on the Lamptron adapter? Can't find much information about it...

Any help is desired.

Cheers, Leic
 
I suspect you are correct in all that. The web page info for that Hub does not claim to be able to control the speed of any 3-pin fans connected to it, so I doubt it can. Almost no 4-pin fan Hubs can do that job.

HOWEVER, almost is not all. There is one unit called the Phanteks PWM Hub that can do exactly as you wish. Like other Hubs it connects to a PSU power output for fan power, and to a mobo fan header that MUST be using the new PWM Mode so it can get the PWM control signal. But it is different in that it does convert from the PWM Mode to the older 3-pin Voltage Control Mode for all its eight outputs. Its max load specs are 1A (12 W) max per output port, but 2.5 A (30W) max in total. All output ports are 3-pin.

3-pin fans can have their speed controlled only by the older Voltage Control Mode. 4-pin fans are best controlled using the new PWM Mode, but they CAN be controlled also by the older Mode because they were designed with this backwards compatibility feature. But there is a small problem using 4-pin fans with this Hub. The spacing of the output ports does not really allow the wider connector of a 4-pin fan to fit on. But there's an easy solution to that, too. The Hub comes with two small Splitters to allow you to connect two fans each on a couple of its outputs. You can use those to connect two of your 4-pin fans to each of two Hub ports, and then it works!

A mobo header can deal with a speed pulse signal coming back to it from only ONE fan. So this Hub, like all others, will send back to the host header the speed of only the fan plugged into its WHITE port #1, and ignore all the others. That's what it should do. This has no effect on speed control. But it does mean that your system cannot monitor the speeds of ALL your fans for FAILURE. So from time to time YOU must check that all the fans are still working.

I recommend you do NOT do one of the instruction details with this unit. Its instructions say to connect the Hub to the CPU_FAN header, and then to connect the actual CPU cooler to the white Port #1. That is for one reason only - on some earlier mobos the only fan header that you could rely on to use the new PWM Mode of control was that CPU_FAN header. But today most mobo SYS_FAN or CHA_FAN headers can be configured to use either PWM Mode or Voltage Control Mode (aka DC Mode). So you should plug the Hub into one of those, and NOT connect your CPU cooler to the Hub. Just connect that cooler to the CPU_FAN header of the mobo. Then be sure to connect one fan to the white port #1 so it does get a speed signal to return to the host header. Then be sure that the SYS_FAN or CHA_FAN header you are uisng is set to use PWM Mode. Also verify in BIOS Setup that the guide for the case fans connected to the header is the temperature sensor on the mobo, and not the one inside the CPU chip.

So that can do what you need. But we have not yet dealt with how to do this without that particular Hub. You have not told us what mobo you have, and we need that maker and exact model number to see whether there is an easy answer. Since many mobos do allow you to specify the Mode of control each header uses, you may be able to configure to control the 3-pin fans from one header set to DC Mode, and the 4-pin fans from another set to PWM Mode. IF you can do that, you may be able to do it with SPLITTERS, rather than a Hub. A Splitter is a simpler (and cheaper) device that merely connects all its fans in parallel to one header. But that means that all the power for that fan group must come from the header, and the header normally is limited to a max 1.0 A current flow. So you need to get the max current consumption specs for all your fans, and add up all the fans in one proposed group to see if they all can be connected to one header within that limit. Since almost all Hubs (except the Phanteks PWM Hub as above) distribute power and control signals to their fans only in PWM Mode, they can NOT control the speeds of 3-pin fans. Thus, a Splitter and a fan header that uses DC Mode is the common way to control a group of 3-pin fans. To tell the difference between Splitter and Hub, note that a Hub MUST have an arm that plugs into a power output from the PSU, whereas a Splitter has no such connecting cable. Do NOT rely on the "name" of the device you consider - sellers often confuse the use of "Splitter" and "Hub". Although the most common Splitters have two outputs, you can find ones with more.

So, give us your mobo specs and we can help advise on those simpler possibilities.
 

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