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I just bought a cheapo fan like this on Ebay, and it's intended to be used in a costume for Halloween:

http://www.ebay.com/itm/Computer-VGA-Video-Card-Heatsink-Cooler-Cooling-Transparent-Fan-40mm-12V-2pin-x-/181701435335?hash=item2a4e3fdfc7:g:mqQAAOSwPYZU-H39

1) It's 12V, which is fine, but I'd like it to go slower. Is this possible, or is it simply a matter of on/off?

2) If the answer above is yes, would a slower fan draw less power from the batteries?

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  • \$\begingroup\$ Try running it from Pulse Width Modulated 12V DC. Not all fans are happy to run this way but it will allow you to vary the speed using a potentiometer. PWM can be achieved using a microcontroller and a mosfet to drive the high current load. \$\endgroup\$
    – user98663
    Oct 9 '16 at 18:29
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There are multiple ways of slowing it down, which would all result in the fan drawing less power. 3 options I can think of

  1. Add a potentiometer in series with the power cable. This would allow you to change the speed quite easily. This is the simplest method but in terms of power quite wasteful because you lose power over the potentiometer.

  2. control the fan using pwm. This could be with a microcontroller or just a 555 oscillator through a transistor. This adds a bit of complexity but is more efficient powerwise.

  3. Have a constant current circuit. This would be done with analog electronics, also more power efficient.

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  • \$\begingroup\$ Hi, and thanks for your answer. Would you mind sharing examples on how I can achieve #2 (with a 555 timer) or #3? Preferably with a link to a simple diagram or something so that I can play with my breadboard. I tried #1 with a (too large) potentiometer, but the fan seemed to either be switched on or off. Later this week I'll get a shipment of more suitable potentiometers, and can test this option then. \$\endgroup\$
    – Pedery
    Oct 11 '16 at 6:14
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    \$\begingroup\$ instructables.com/id/… Thats a simple 555 implementation. However you will probably need a transistor on the output to drive the load. I don't think that the 555 can drive that much current without blowing \$\endgroup\$
    – Makoto
    Oct 11 '16 at 14:04
  • \$\begingroup\$ Cool, that looks perfect. It's just 8xAA (or a 9V), so we're not talking about lots of power. I have all those parts too, except I'll swap the transistors for a 2N2222a, which I assume is ok. \$\endgroup\$
    – Pedery
    Oct 11 '16 at 20:29
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    \$\begingroup\$ yeah, the 2N2222a will probably be fine, it might get a bit warm though :) \$\endgroup\$
    – Makoto
    Oct 11 '16 at 20:45
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  1. Computer-grade brushless DC fans do have a range of voltages to operate. It is quite common to have a linear (or other) voltage regulator that slows down fan's rpm (usually to reduce audible noise). The working range however varies, some fans can operate down to 3-4V and slow down to 500-800rpm. 7V should be a reliable target.

  2. yes, with lower operating voltage the fan will consume less current.

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