Using Zeners to Reduce Fan Speed

[bgavin]

I want to experiment with using Zener diodes as voltage drops to reduce noisy 12v computer fans.

http://www.cpemma.co.uk/diodes.html

Does anybody know where I can source these diodes in the USA in small quantities, and a resonable price?

[kc8adu]

Re: Using Zeners to Reduce Fan Speed

radio shack?
digikey for sure.
just pad the order with caps,ect to dodge the $5 handling.

[WNG]

Re: Using Zeners to Reduce Fan Speed

PSUs are pretty well regulated. Simple series resistance is all you really need.
KISS principle is best here. IMO, 50 Ohm resistors are a good start for voltage drops. Put them in series or parallel to get to the desire fan dB.

[Harvey]

Re: Using Zeners to Reduce Fan Speed

Or you could just connect the fan between the +12 (positive) and +5 (negative) and run the fan on 7V.

[bgavin]

Re: Using Zeners to Reduce Fan Speed

The 7v solution runs a good risk of smoking the PSU. This warning is well documented on many of the testing sites. For my last parts order, I bought a few of the $1.95 9v solutions using a series resistor. Even if I swap out the resistor later, the cables and three connectors are worth the price.

The resistor method does work, but limits the startup voltage to the fan. I'm told the Zener allow full voltage at startup.

The first cadidate for the slow-down is a group of 92mm Panaflo 12H I have in stock. These damn things are irritatingly loud. I bought several because they have the BX tach encoder required by Dell system boards. My daughter is using a Dimension 2350 that I got when I customer got a new machine. I recapped the board and PSU, and it runs just fine... and too loud with the Panaflo.

I did a cursory look at Digi-Key but didn't find what I wanted. I've never ordered, so I should take a closer look. I need some PSU caps, etc. Wai Fong is flat out of MCZ in the values I need.

[yanz]

Re: Using Zeners to Reduce Fan Speed

The 7v solution runs a good risk of smoking the PSU. This warning is well documented on many of the testing sites.

Hmm could you share the links? Im interested in this.

Perhaps using a good psu vs cheap psu makes any differences? Or maybe it's the same dangerous both psus could face if using 7v methode..

[gonzo0815]

Re: Using Zeners to Reduce Fan Speed

I have such connectors at home, bought them for several years. Never had a single problem.
ATM i don`t see, why this should pose any risk for anything. As long as there is no short, i don`t think it is dangerous.
May be some of the smarter people may explain it, why this could pose a risk. Up to then, i think this is one of the modern urban myths, grown on half knowledge.

[bgavin]

Re: Using Zeners to Reduce Fan Speed

Hmm could you share the links? Im interested in this.

http://www.silentpcreview.com/article6-page1.html

[yanz]

Re: Using Zeners to Reduce Fan Speed

ok, thanks! i'll check it...

[Fatal0E]

Re: Using Zeners to Reduce Fan Speed

I have a bunch of these 7v adapters, typically work well with good power supplies but I have had many computers not turn on with them hooked up.

[bgavin]

Re: Using Zeners to Reduce Fan Speed

Fry's Electronics stocks various Zeners that will do the job. I picked up the NTE5067A in 3.9v, and NTE5069A in 4.7v. They come in two packs for 99 cents per pack.

I have a Panaflo 92mm H12 (2850 rpm) that I want to tone down. This one is mounted in the rear of a Dell case, and is objectionably loud. Funny thing, I have the same fan running internally on a Thermalright XP-90 heat sink, and it is very usable.