[mythtv-users] Slightly OT - Controlling the CPU fan
anaerin at gmail.com
Sun Aug 21 23:00:14 UTC 2005
On 21/08/05, Nick <knowledgejunkie at gmail.com> wrote:
> On 8/21/05, Lee <mythtv at varga.co.uk> wrote:
> > >> One of the other suggestions I've seen but not tried is to use 12v
> > >> fans but run them off the 5v supply so they spin slow and quiet.
> > >
> > Noooo..............
> > Don't try this at home folks!! Running 12V fans at 5V is dangerous, they
> > have a habit of NOT starting reliably.
> > It may start OK when the lids off, but may not when it's back under the
> > TV... With possibly tragic results...
> Exactly. Fans may also not start reliably if you give them 7V (using
> the 12V and 5V feeds) so sometimes leaving them on the 12V is the
Generally, 7v is enough to start most fans. 5v would not be.
However, the very best way to run fans at slow speeds would be to use
a PWM circuit system, that way the fan motor always has 12v to turn
it. The only disadvantage of PWM is a possible "growling", but that's
generally only found at VERY low speeds, and isn't audible if the PWM
Frequency is above 20khz.
Robert "Anaerin" Johnston
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