However, this factor will not really influence a lot your power rating calculation later.Ĥ. You should realize, however, that when they all are starting up from stalled, the momentary (1 to 2 seconds) current will be about three times that. This is the max current at full 12 VDC supply when they are running. Add those currents because your several fans are in parallel. Calculate its individual current if necessary.ģ. For each fan, get its rated current flow (or Wattage rating) at full speed with a 12 VDC supply. Determine how many fans you will run together in PARALLEL from this one voltage source.Ģ. But you want to DIY, so here's an outline of what you need to do.ġ. The best way to do this is with a pre-engineered third-party fan speed controller because all the fancy design requirements have been done for you.

Thus, you CAN alter the speed of a 4-pin fan by changing the voltage supplied to its Pin #2. It also does NOT receive any PWM signal to modify the voltage supply, so it just does whatever the voltage allows. In such a case, the fan receives NOT a constant 12 VDC on Pin #2, but a voltage that is changed by the mobo port. 4-pin fans have a backwards compatibility feature so that they DO work under Voltage Control Mode on a 3-pin header. What geofelt said about 4-pin fans on a mobo 3-pin header is wrong.

Download 4 pin fan pinout