Michael Scott

Hi All
Sorry this is a bit OT.
I have a couple of small fans I want to use to cool a heat sink. One is on a small heat sink and looks as if it was intended to cool a CPU, the other is off a defunct DVD recorder. Both have three wires, red, black and white. DC applied to the red and black cause the fan to rotate. The question is, what is the purpose of the white wire?
Thanks in anticipation!
73, Mike, G3LYP

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