Re: Fans

Nick Peckett G4KUX

Hi Mike,
The white wire is used to count pulses from the fan and used to control it’s speed. Be careful with computer ect DC fans as they use electronic circuitry to control the speed and are vulnerable to high RF fields. I have blown several up due to this. You need to apply ferrite beads as close to where the wires terminate on the fan as possible, and decoupling capacitors are a good idea as well. I generally run them constantly on TX and employ a 50C thermal switch on the heatsink which runs them continually if the heatsink temperature demands it.
Nick G4KUX

Sent: Wednesday, May 04, 2016 11:16 AM
Subject: [ukmicrowaves] Fans

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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