Re: reducing 12V+ source voltage with a potentiometer
- From: Spehro Pefhany <speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 18 Apr 2005 15:51:28 -0400
On 18 Apr 2005 10:46:46 -0700, the renowned "Joseph"
<spmok2@xxxxxxxxxx> wrote:
>I would like to reduce the 12V+ source voltage going into computer fans
>with potentiometers place between the 12V+ and the fan. I am unsure
>what Ohm rating potentiometer I need to get could someone please help.
>
>
>All I remember from physics class was that V=IR formula. So I guess
>that means R=V/I = 12/I The fan has a label that says 0.8A on it. So
>I guess that means R=12/0.8 = 15 Ohms max ? Kinda small? I only have
>on hand a potentiometer that say 15K ohm.
>
>Could someone please share me their experience using pots to
>dynamically reduce a 12V source voltage.
Try this circuit: http://cache.national.com/ds/LM/LM117.pdf
(first schematic, but with a 2K pot rather than a 5K). You don't need
the output cap, but I suggest putting the input cap on there, so 4
parts. It might need a small heatsink, depending on the current the
fan draws.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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