In article ,
Derek Geldard writes:
On Sat, 15 Nov 2008 09:57:51 -0800 (PST), wrote:

Can someone tell how I would size a potentiometer for a circuit to
control a simple 12v fan ( ex pc).

Fan - Roughly 12vdc/ 0.15A/ 1.8Watts

Input Power - Old movile phone charger - 6v upto around 12v DC
depending on model I find in the garage.

Am making a magnetic stir plate and using the fan with a couple of
magnets stuck onto it as the main drive unit

Thanks for your help

I don't know how the fan would behave, PC fans have brushless solid
state DC motors they might need almost the full 12 v to run the
electronics. Also 0.15A will be the average, they might draw their
current in short heavy pulses.

They're often run in PCs at reduced voltage. Minimum is generally
7V to guarantee starting. With intelligent control, (higher starting
voltage, then dropping back), they can be run significantly lower
than this. In practice, I've found very few 12V ones which won't
start even on 5V.

Not sure they'll have the ideal torque profile for a stirrer.

--
Andrew Gabriel
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