Quote:
Originally Posted by BRG75
... the 2 speed fans use 4 brushes, with two of them "doubled up".
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Yes Mike, this was news to me too until Steve (
Arctic) sent me a board from a 2 speed 3 wire system. On this the positive supply has two brushes wired in parallel and one earth brush for the slow speed. The fourth brush is used as an additional earth to produce the fast speed.
I have never inspected a board from a 2 speed 2 wire system but I'm assured that this design uses a pair of brushes wired in parallel both on the positive supply and the earth. The speed reduction is, of course, achieved by switching in the resistor.
Simon