Best way to power a 12vdc fan from 25vdc for an Aleph30 - diyAudio
 Best way to power a 12vdc fan from 25vdc for an Aleph30
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 6th December 2005, 06:40 PM #1 diyAudio Member     Join Date: Oct 2003 Location: San Jose Best way to power a 12vdc fan from 25vdc for an Aleph30 I'm building an Aleph30 and wanted to include a low noise fan in the chassis. The Aleph30 has a 25VDC powersupply and the fan is 12vdc at .06amps. What is the best and easiest way to drop the voltage for the fan? Is a voltage divider needed or would a resister in series with the + slide of the fan work ok? Thanks for the suggestions. -David
 6th December 2005, 08:01 PM #2 diyAudio Moderator     Join Date: Apr 2002 Location: Chatham, England Wouldn't it be easier to use a 24V fan? Otherwise just use a normal 3 pin regulator, though you may want to put a trimpot in the circuit to fine tune the speed. __________________ Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
 6th December 2005, 09:06 PM #3 diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany Hi, a simple series resistor will do. Normally 12V will be too much for really low noise. I would try 8 or 9V. At ca. 45mA you will need a (25-9)/0,045=355ohm resistor. Power needed 0,045^2 x 355 = 0,72 Watt You could try 330 or 390 Ohm resistors of 2 watts to be on the safe side. William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 6th December 2005, 09:15 PM #4 diyAudio Member   Join Date: Sep 2004 Location: none Fan Put two 12volt fans in series... __________________ none
 6th December 2005, 10:55 PM #5 diyAudio Member   Join Date: Nov 2003 Location: France dand le sud from the secondary a bridge of diode C : 01µF LM317 Rv 5K + 240R C : 200µF and one can regulate speed or Instead of few fans at 12v, anyone try many fans at 7v? Phill __________________ rencontres internet
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Join Date: Mar 2001
I like this circuit. You can vary the fan speed, but it gives an
extra kick on turn-on to get the fan spinning reliably, and then
you can idle it at quite low speeds if you want.
Attached Images
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 6th December 2005, 11:14 PM #7 Banned   Join Date: Mar 2005 Location: Australia I think Mr Pass's method has got to be the best with the added bonus of varying the speed and silent operation
 7th December 2005, 01:37 AM #8 diyAudio Member     Join Date: Apr 2002 Location: Llanddewi Brefi, NJ simplest way -- without wasting any energy -- get yourself an LM3524 (SG3524) and PWM the fan circuit -- kind of an old circuit but National Semi has an application note which shows exactly how. or if you are using a torroid -- just create another secondary by winding a few extra turns with #24 insulated wire around the core -- I did this with my LM4780 bridged amp which required a fan.
 7th December 2005, 08:36 PM #9 Banned   Join Date: Mar 2005 Location: Australia oh yeah i like the second idea too if the transformer allows you to do that if you make the winding with taps you also vary the speed and the idea is intrinsicly efficient thanks jackinnj cheers
 7th December 2005, 09:21 PM #10 diyAudio Member   Join Date: Dec 2004 Location: Cincinnati, Ohio The simplest cheapest way I can think up to give regulated 12V is with a 180 ohm resistor and a 12V 1W zener. You could add a pot to this to give variable speed. The watt or two wasted here I dont think is significant in an Aleph. __________________ Be sure your foil hat has a good low impedance ground.

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