Case fan connectors

computer-buildingfan

I've built around 5 systems in my entire life. I've attached every chassis fan (case fan) on the 4-pin MOLEX connector ever since.

I've noticed that there is a 3-pin connector there, but assumed that it was for "older" PSUs but now, I've noticed that my board has a 3-pin CHA_FAN header (which, after further reading, can enable "fan control").

So my questions are:

  1. What exactly is the 3-pin used for?
  2. If I plug the 3-pin connector into the board, should I also plug the 4-pin molex?
  3. Why should I plug my case fans to the 3-pin header on the motherboard?
  4. If I have more than 1 case fan, can I daisy-chain the 3-pin connectors and plug it into the single 3-pin header on the board?
  5. If I plug the case fan into the 4-pin molex, what happens to fan-speed control?
  6. Why is fan-speed control important?

Best Answer

Actually, the 3-pin connector is newer.

  1. The 3-pin connector provides power to the fan, and optionally (if the fan supports it), monitoring of the speed of the fan.
  2. Does your fan have two wires/connectors‽
  3. If the fan supports monitoring, then you get the added benifit.
  4. Not as such. There may exist special adapters, but it’s better to make use of separate connectors (most boards have three). If the fans support speed-monitoring, then you definitely can’t daisy-chain them (or at least not expect it to work, and possibly damage something).
  5. Nothing. Speed-monitoring and speed-control are separate. The third wire in the fan allows it to “report” its speed to the motherboard. Obviously connecting it to the two wires of a four-wire Molex connector won’t support that. The motherboard controls the speed of the fan by adjusting the voltage it provides to the fan. It can only do that if the fan is directly connected to the board, not if it is connected to the PSU.
  6. Fan speed-monitoring and control allow you to automatically raise or lower the speed of the fans as necessary, either via the BIOS, or a program like SpeedFan. This allows you to keep them running fast for more cooling when the system is hot, and keep them running slow (or off altogether) when the system is cool; providing you with a quieter system (fans can be quite noisy).
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