Power supply fans that only runs when needed

glassjoe · Post by **glassjoe** » Wed Apr 09, 2003 6:13 pm

I'm building a small mini-itx server for my apartment and since I plan on running this server 24/7 I'd like to know what power supplies are available that have fans that only operate when needed.

This is sort of similar to how the fans in my laptop work. They are off most of the time, but start up every once in a while and then stop about 30 seconds later. And whenever I play fps games, they run constantly at full speed.

I thought about using a morex 55w fanless power supply, but I still like the idea of having at least one fan available just in case it's needed. Just as long as it runs only when it's needed.

So do most power supply fans these days still run constantly? I've heard of power supply fans that adjust their speed depending on the temp or can be adjusted manually, but do these fans ever stop completely, or do they just slow down a bit?

Post by **Rusty075** » Wed Apr 09, 2003 7:38 pm

Yes, in all the power supplies that have fans the fans spin all the time. Most of them are thermally controlled, that is when the PSU is cool the fan gets less voltage and spins slowly making less noise. With the right fan is it nearly silent when at low speed.

But if you do want to not spin at all it would be a simple mod to do. All you'd have to do is put a resistor in the line to the PSU fan. If you size the resistor right (or use an adjustable reostat) the voltage going to the fan at low temps will be below it's start-up voltage. As the temps rise so will the volts, until it reaches to the point where the fan turns on.

d_kay · Post by **d_kay** » Wed Apr 09, 2003 11:27 pm

But isn't the problem that a 300W PSU always needs active cooling. I mean, there is probably a minimum of heat being generated that is greater than the morex 55W, even if the system is idle. And you have to know how hot your PSU is allowed to be to be able to design the cutoff for the fan.

glassjoe · Post by **glassjoe** » Thu Apr 10, 2003 2:42 pm

Here's someone who's found some fanless power supplies.

http://www.seanm.ca/eden/psu.html

Since my lightweight server is only going to have one client (me) and will only need enough power to run the motherboard, a 3.5" hard drive, and the RAM, I decided to go with a 60w external brick-type power supply. And then maybe I'll install a separate panaflo case fan.

The author of the web page also mentioned a 300W PSU (TK Power TK300PO-60) that runs off of no fan whenever it's at <= 80W. I can't find a place to buy this PSU anywhere though. And I only know of one review.

http://www.minervatech.net/reviews/silent_demo/

Has anyone tried this PSU or know anything else about it?

How many watts does an idle PC really need? I mean, I think my small server will only need about 30 watts, but I would think that a desktop PC thats just sitting idle shouldn't take up more than 60 watts. Well, maybe not a Pentium 4 desktop.

glassjoe · Post by **glassjoe** » Fri Apr 11, 2003 11:06 pm

Err... maybe I should have looked around SPCR a bit more...

http://www.silentpcreview.com/modules.p ... =18&page=1

Post by **Rusty075** » Fri Apr 11, 2003 11:22 pm

Yeah, that search function is neat

sam i am · Post by **sam i am** » Tue Apr 22, 2003 9:07 pm

I think my small server will only need about 30 watts, but I would think that a desktop PC thats just sitting idle shouldn't take up more than 60 watts.

You don't mention which mini-itx motherboard you will be using, but the EPIA 5000 uses 15W max. It is more like 7W idle (note this includes RAM). Add a harddrive and you are looking at less than 25W max, less than 8W idle assuming you put the harddrive in standby mode.

A desktop machine with a Pentium 4 needs 55W just for the Pentium

Add in a Radeon 9700, hard drive and other motherboard components and you are already at 100W idle minimum.

larrymoencurly · Post by **larrymoencurly** » Wed Apr 23, 2003 11:09 pm

My 1.7GHz Celeron drew about 70W (4.5A @ +3.3V, 11.5A @ +5.0V), but I think that it's 0.18 micron, not 0.13u.