Using a Zener Diode to slow PSU fan *pictures*

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fraz
Posts: 45
Joined: Sat Aug 16, 2003 9:52 pm
Location: Australia

Using a Zener Diode to slow PSU fan *pictures*

Post by fraz » Sun Aug 01, 2004 9:10 pm

I have tried various things over the past year and and I'm finally happy with my PSU's noise, so I thought I'd share it with everyone since I haven't seen it documented before.

The story so far:
I initially tried using 2x 5W resistors in parallel soldered in line with the stock fan, and a switch to choose mid or low speed. One was 82 ohm, the other 47ohm one was parallel to that with a switch to allow the electricity to bypass the larger resistor. That worked well enough, but the HD temps were a bit high, and the noise/airflow ratio wasn't too good.

Enter the Panaflo
I eventually bought a Panaflo and 4 blue vibration isolators. This moved significantly more air for the same amount of noise as the previous low speed setting. My HD temp was only 14 above ambient.

12V -> Zener -> 8.1V
I had heard in various places that zener diodes do a better job of dropping the voltage in a controlled manner, and that the fan still gets full current to start and is less likely to seize. I had heard most people here using Fanmates or the 7 volt trick to drop the voltage, though couldn't find much about Zener diodes. So I bought a Zener diode and tried it, and found it worked very well:

Here's what I did:

Image
Photo of inside my PSU before. The red and blue wires go to the Panaflo.

INSERT OBLIGATORY WARNING HERE:
Though I didn't change any of the actual PSU circuits, it's still dangerous inside if you're not careful! Make sure the PSU is unplugged, and preferable hadn't been turned on recently!

Cut the positive (usually red) wire to the fan, and strip a small section of insulation. Though it really doesn't matter which wire since the Diode will be put in series with the fan.

Image
Thats the zener diode sitting on the edge waiting to be soldered in.

I added another couple of yellow wires to a switch mounted on a blank PCI drive bay cover. The other end of the wires I fed through the ventilation slots on the front of the PSU, and soldered in parallel with the Zener diode. The Zener diode must be soldered so the black band faces towards the positive, otherwise it won't drop the voltage by it's nominal amount.

Before soldering, feed a length of heat shrink tube into the yellow and red wires so it can be slide back over the diode and shunk to insulate it afterwards.

Image
Cut some of the excess wire from both ends of the Diode, and bend the end around to form a tight eye hook. Feed the other two wires though the eyelet, and fold them back too. This will help form a stronger solder joint.

Solder each end, and then put heat shrink tube in place. I used a lighter to shrink it after practicing, just don't get too close.

Image
Here's the finished product.
Zener diode in line with the positive wire. Black band facing towards the positive (PSU fan connection). And yellow wires going to a switch mounted on the case to toggle 12V/8.1V.

Switch: ,-sw-,
POS ------|<-------- FAN ------- NEG

The diode I used was:
3V9 1W 1N4730

Panaflo rating: 12V * 0.1A = 1.2W.
However I read somewhere the actual current is around 70mA.
So 1 Watt should be fine for a Panaflo, though I would have used a high rated one if I could get them.

My HD temp is now only 1-2 deg warmer, and I can still speed the fan upto full speed during summer. But the computer is now nearly inaudible, since the panaflo is the only case fan. (It's on an old pentium I server in case you're worried, low power)

Hope others find this useful! Someday I'll make an entry in the modded system section, with the other things i've done to silence this system.

bchung
Posts: 24
Joined: Sun Jul 11, 2004 4:36 pm

Post by bchung » Mon Aug 02, 2004 6:49 am

Thanks :D

Skylined
Posts: 161
Joined: Sun Dec 22, 2002 8:40 pm
Location: Uruguay
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Post by Skylined » Mon Aug 02, 2004 7:54 am

Reminds me of cpemma's diobus.
http://www.cpemma.co.uk/sdiodes.html
[url=http://www.ntntelectronica.com][b]Música Electrónica : : n t n t e l e c t r o n i c a . c o m[/b][/url]

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