DIY power up for small fan

akruppa · 2009-04-17, 17:22

I suppose this technically belongs in Hardware though it's rather different from the other threads here...

I have a small fan for my Northbridge chip. The NB fan connector on the motherboard does not take a speed signal, nor does the fan supply it. (Edit: changing fan speed with fancontrol did not work, either) It nominally takes 12V but is pretty noisy. It can run at 5V, too, and is very quiet then. The NB is meant to be passively cooled but gets a bit hot, a little extra air flow is all I need, so running the fan at 5V would suffice. However, the fan does not spin up reliably with only 5V - once it spins (e.g., by manually spinning it up), 5V are enough to keep it running.

I'm pondering a small circuit that applies 12V to the fan for a few seconds at power-up, then switches to 5V. This should be fairly trivial... an RC delay, a trigger and a switch. I don't have much of a clear idea how to design the circuit, though... if anyone has a suggestion, I could solder the stuff together without problem. Easy-to-get parts would be a plus.

Any suggestions?

Alex

KriZp · 2009-04-17, 18:46

how about running it at 7V, connecting 12V and 5V?

Uncwilly · 2009-04-17, 18:51

That is about as quick and dirty as one can get.

xilman · 2009-04-17, 19:50

Quote:

Originally Posted by KriZp

how about running it at 7V, connecting 12V and 5V?

I'm impressed!

Paul

akruppa · 2009-04-17, 20:05

Quote:

Originally Posted by KriZp

how about running it at 7V, connecting 12V and 5V?

Lol, I'll try that... though you kinda spoiled the problem with your horribly pragmatic, smack-in-your-face obvious solution!

I was actually looking forward to soldering something...

Well, maybe it'll be too noisy at 7V or won't spin up, and I might get to solder something after all.

Alex

Batalov · 2009-04-17, 20:54

Seriously, you may screw up both your 12V and 5V at the same time, -- for the rest of the computer. EE is not "only" math, you don't wanna connect these rails, really.

You may want to feed from 12V through a some small R/C and that's all, no triggers, no switches. If you can determine the resistance of your fan and match it with a resistor, than you will have 6V on it, when the capacitor is charged. Then calculate the C... you know.

You can also do a variable resistor on the back bracket, ...even Tuniq Tower doesn't shy away from this solution! It comes with it.

KriZp · 2009-04-17, 20:59

It's a pretty common solution I think, certainly not my idea

You can always make a switch between 5-7-12 volts if you have a strong urge to solder something.

akruppa · 2009-04-17, 22:10

I certainly wouldn't hook any significant load between the 12V and the 5V rail, but the fan has 0.6W power draw when running at 12V so I don't expect the PSU to mind it very much.

Alex

frmky · 2009-04-18, 00:13

Quote:

Originally Posted by akruppa

I certainly wouldn't hook any significant load between the 12V and the 5V rail, but the fan has 0.6W power draw when running at 12V so I don't expect the PSU to mind it very much.

Remember that the power draw is much higher until the fan gets up to speed. It's transient, but I'm not so sure the supply won't mind.

cheesehead · 2009-04-18, 01:02

Quote:

Originally Posted by KriZp

how about < snip > connecting 12V and 5V?

I still remember being at work one Saturday morning 30 years ago. I was in the "machine room", and suddenly noticed wisps of smoke rising from all of the tape drives. I yelled "Fire!", which alerted the electrical workers on the other side of the room that they had connected a 220V line to a 110V circuit.

Five years later, at a different employer, I arrived one morning to find that the DEC employees who had installed a new VAX backboard (DEC had warned us that our warranty would be invalided if any non-DEC employee did the installation) had connected 12V to 5V for a while. However, they assured us, there was no damage, the system still worked fine, and our subsequent occasional system failures were completely unrelated to that incident.

Andi_HB · 2009-04-18, 05:28

I think this is what you need.
Ue = 12V DC <- not AC!
Ua = 5V DC
If you take 7806 instead 7805 you have 6V Ua

Regards Andi_HB

2009-04-17, 17:22	#1
akruppa "Nancy" Aug 2002 Alexandria 2,467 Posts	DIY power up for small fan I suppose this technically belongs in Hardware though it's rather different from the other threads here... I have a small fan for my Northbridge chip. The NB fan connector on the motherboard does not take a speed signal, nor does the fan supply it. (Edit: changing fan speed with fancontrol did not work, either) It nominally takes 12V but is pretty noisy. It can run at 5V, too, and is very quiet then. The NB is meant to be passively cooled but gets a bit hot, a little extra air flow is all I need, so running the fan at 5V would suffice. However, the fan does not spin up reliably with only 5V - once it spins (e.g., by manually spinning it up), 5V are enough to keep it running. I'm pondering a small circuit that applies 12V to the fan for a few seconds at power-up, then switches to 5V. This should be fairly trivial... an RC delay, a trigger and a switch. I don't have much of a clear idea how to design the circuit, though... if anyone has a suggestion, I could solder the stuff together without problem. Easy-to-get parts would be a plus. Any suggestions? Alex Last fiddled with by akruppa on 2009-04-17 at 17:33

2009-04-17, 20:54	#6
Batalov "Serge" Mar 2008 Phi(4,2^7658614+1)/2 2516₁₆ Posts	Seriously, you may screw up both your 12V and 5V at the same time, -- for the rest of the computer. EE is not "only" math, you don't wanna connect these rails, really. You may want to feed from 12V through a some small R/C and that's all, no triggers, no switches. If you can determine the resistance of your fan and match it with a resistor, than you will have 6V on it, when the capacitor is charged. Then calculate the C... you know. You can also do a variable resistor on the back bracket, ...even Tuniq Tower doesn't shy away from this solution! It comes with it. Attached Thumbnails Last fiddled with by Batalov on 2009-04-17 at 21:13 Reason: You can also do a variable resistor

2009-04-18, 05:28	#11
Andi_HB Mar 2007 Germany 264₁₀ Posts	I think this is what you need. Ue = 12V DC <- not AC! Ua = 5V DC If you take 7806 instead 7805 you have 6V Ua Regards Andi_HB Attached Thumbnails Last fiddled with by Andi_HB on 2009-04-18 at 05:37

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2009-04-17, 18:46	#2
KriZp Feb 2007 10000111₂ Posts	how about running it at 7V, connecting 12V and 5V?

2009-04-17, 18:51	#3
Uncwilly 6809 > 6502 """"""""""""""""""" Aug 2003 101×103 Posts 10011001011010₂ Posts	That is about as quick and dirty as one can get.

2009-04-17, 20:59	#7
KriZp Feb 2007 3³·5 Posts	It's a pretty common solution I think, certainly not my idea You can always make a switch between 5-7-12 volts if you have a strong urge to solder something.

2009-04-17, 22:10	#8
akruppa "Nancy" Aug 2002 Alexandria 2,467 Posts	I certainly wouldn't hook any significant load between the 12V and the 5V rail, but the fan has 0.6W power draw when running at 12V so I don't expect the PSU to mind it very much. Alex