reducing 12V+ source voltage with a potentiometer

Try this circuit:

(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

fans

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help.

So

have

reward"

"Joseph" schreef in bericht news: snipped-for-privacy@f14g2000cwb.googlegroups.com...

There are several ways to control a 12V fans speed but a potmeter is the worsed. You can try to find a linear voltage controler or a PWM circuit. I have no circuits here at the moment but a little googling will make you find what you need.

petrus bitbyter

I suspect it actually reads 0.08A

It's not the ideal way to control a fan but it should work ok. You'll need a 'pot' capable of dissipating a watt or so. Cermet types are likely to be best suited. Or try a fixed resistor of anywhere say between 150 and 470 ohms and see what the effect is like.

Graham

You are correct about a little googling. Here is a site that Joseph might find interesting.

Joseph that idea of adding diodes just might make your fan less noisy and still keep your mother board happy. Experiment with the number of diodes in series with the fan.

Have Fun, John Crighton Sydney

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help.

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thats the approx R of the fan, not the R of the pot you want. But its not far off. A bit higher would give more v reduction range.

I'd double check your fan ratings though, that does sound high.

Its the simplest way - for a one off theres no reason to get into complex electronics whena simple cheap pot does the trick. Either use a 1w pot or else put your chosen pot in the airstream. Or you can just use a bit of resistance wire and a croc clip etc to tap off where wanted. R wire: heater elements, light bulb filaments, etc.

NT

fans

help.

theres a simpler way that might do what you want: connect the fan to 7v instead of 12v. +to +12v, - to 5v.

NT

Cheap and dirty. Put a 12vlot lamp in series with the motor. For faster motor speeds, use higher current lamps. Moundt a 1-hole mounted lamp holder on the back of the machine for easy lamp changes. Also provides some light back there when switching cables and such.

But keep in mind that using this regulator will leave only about

I think this is the best way. You could mount a switch on the case, and switch between 12 volts, 7 volts or 5 volts, all easily available. That should give enough options. How about a 3T2P switch for simplicity?

Although I have to admit, a non automated system that cuts the fan speed makes me nervous. I'm sure I'd forget about it and leave it on low speed while putting a heavy load on the system.

I used a rheostat to reduce fan speed--it absorbs heat well and can be mounted on the front of the case with a semi-attractive knob! make sure you get one thats rated for the number of watts you intend to run through it.