[mythtv-users] Slightly OT - Controlling the CPU fan

[Robert Johnston]

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
> best.

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