DIY power up for small fan - Page 2

akruppa · 2009-04-18, 13:06

A problem with the constant-voltage solutions is that the fan needs relatively high voltage to spin up, but then only little to keep running, and I'd like to run it at very low speed. I'm now thinking about connecting 12V to the fan via a capacity (as in Batalov's suggestion) and 5V via a diode. Or I'll just use Batalov's suggestion.

Alex

KriZp · 2009-04-18, 14:03

Quote:

Originally Posted by Batalov

Seriously, you may screw up both your 12V and 5V at the same time

Probably best to listen to those that really know what they are talking about.

The cpu fans on my old dual celeron BP6 are powered through a simple circuitry consisting of a 3-way switch and 2 resistors. Input is 12V. I imagine it switches between parallell and serial resistors, and straight 12V. It is probably not specced for running as powerful fans as I have connected to it, because it appears to have overheated. I got it from a friend, apparantly it came with his lian-li case.

frmky · 2009-04-18, 17:18

I think Batalov's solution is the best, but you're going to need a large capacitor to provide the large start-up current needed for enough time while the capacitor is charging. I'd start with at least an 18V 470uF capacitor and go up from there if necessary. If you have an old discrete sound card around that you can sacrifice, it probably has one.

The other way to do it is to use a switch IC. Something like the MAX4622 would work, which will operate on 0, 5V, and 12V and has guaranteed break before make. The time at 12V is fully adjustable by using an appropriate RC on the trigger input.

IronBits · 2009-04-18, 17:41

It's been done that way (using 12v and 5v) to slow fans down for some time now (2002?).
http://www.ocforums.com/showthread.php?t=372297
http://www.silentpcreview.com/article6-page1.html
http://www.hardforum.com/showthread.php?t=1151998
http://www.asktheramguy.com/v3/showthread.php?t=76932
http://www.computerpoweruser.com/edi...03%2F25c03.asp

Google will give you many more hits with ' 7v fan '

Xeon cpu fans were always very noisy, especially them 10,000 rpm one... slowing them down just a tad made it more tolerable.

Just do it.

2009-04-18, 13:06	#12
akruppa "Nancy" Aug 2002 Alexandria 2,467 Posts	A problem with the constant-voltage solutions is that the fan needs relatively high voltage to spin up, but then only little to keep running, and I'd like to run it at very low speed. I'm now thinking about connecting 12V to the fan via a capacity (as in Batalov's suggestion) and 5V via a diode. Or I'll just use Batalov's suggestion. Alex Last fiddled with by akruppa on 2009-04-18 at 13:11

2009-04-18, 17:18	#14
frmky Jul 2003 So Cal 4112₈ Posts	I think Batalov's solution is the best, but you're going to need a large capacitor to provide the large start-up current needed for enough time while the capacitor is charging. I'd start with at least an 18V 470uF capacitor and go up from there if necessary. If you have an old discrete sound card around that you can sacrifice, it probably has one. The other way to do it is to use a switch IC. Something like the MAX4622 would work, which will operate on 0, 5V, and 12V and has guaranteed break before make. The time at 12V is fully adjustable by using an appropriate RC on the trigger input. Last fiddled with by frmky on 2009-04-18 at 17:29 Reason: Add IC solution

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2009-04-18, 17:41	#15
IronBits I ♥ BOINC! Oct 2002 Glendale, AZ. (USA) 10001011001₂ Posts	It's been done that way (using 12v and 5v) to slow fans down for some time now (2002?). http://www.ocforums.com/showthread.php?t=372297 http://www.silentpcreview.com/article6-page1.html http://www.hardforum.com/showthread.php?t=1151998 http://www.asktheramguy.com/v3/showthread.php?t=76932 http://www.computerpoweruser.com/edi...03%2F25c03.asp Google will give you many more hits with ' 7v fan ' Xeon cpu fans were always very noisy, especially them 10,000 rpm one... slowing them down just a tad made it more tolerable. Just do it.