Still, it is the same type of component.Ħ. The units often used for such things are commonly called "pots", short for Potentiometers, but a true potentiometer is a different circuit function and is wired and loaded differently. What you really plan to do, I believe, is install in the circuit in series with the motors (paralleled as as group) and the voltage source a variable resistor. Maybe your variable resistor should have a mechanical stop affixed to it, or maybe you can simply buy a resistor whose max resistance provides this limit for you.ĥ. So, your design should somehow prevent you from giving the fans less than 7 volts. To start a stalled fan you need to supply at least 7 VDC for most units with good bearings. The reality of fan motors and supply voltage is this: at some reduced voltage (often between 5 and 6 volts, but could be higher on an older fan with bad bearings) the fan will stall and will not start up again until the voltage is raised enough. 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.
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