Best way to power a 12vdc fan from 25vdc for an Aleph30 - diyAudio
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Old 6th December 2005, 07:40 PM   #1
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Question 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
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Old 6th December 2005, 09:01 PM   #2
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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.
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Old 6th December 2005, 10:06 PM   #3
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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
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Old 6th December 2005, 10:15 PM   #4
zlast is offline zlast  United States
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Default Fan

Put two 12volt fans in series...
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Old 6th December 2005, 11:55 PM   #5
Phill is offline Phill  France
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from the secondary
a bridge of diode
C : 01F
LM317
Rv 5K + 240R
C : 200F
and one can regulate speed

or
Click the image to open in full size.

Instead of few fans at 12v, anyone try many fans at 7v?

Phill
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Old 7th December 2005, 12:06 AM   #6
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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.
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Old 7th December 2005, 12:14 AM   #7
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I think Mr Pass's method has got to be the best with the added
bonus of varying the speed and silent operation
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Old 7th December 2005, 02:37 AM   #8
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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.
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Old 7th December 2005, 09:36 PM   #9
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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
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Old 7th December 2005, 10:21 PM   #10
Tweeker is offline Tweeker  United States
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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.
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