Need dirt cheap very low power PSU

PSUs: The source of DC power for all components in the PC & often a big noise source.

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kentc
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Need dirt cheap very low power PSU

Post by kentc » Tue Mar 18, 2008 11:42 am

Hello,

I'm gonna add a firewall to my network that'll be very low power and passively cooled:

HP mATX motherboard from VL400 series
PIII/Celeron 600Mhz (12w)
1x PC133 DIMM
1x CF card on IDE bus
1x PCI NIC

With an old Chieftech 300w PSU it draws 22w from the wall. For estetic and noise reasons and because the Chieftechs efficiency is probably under 60% at the extremely low load I want a better PSU solution. Problem is my budget is very close to zero :)

A couple of things I've contemplated:

* Somehow use the old 18.5v Compaq laptop brick I have lying around. What is the cheapest way to get ATX out of that?

* Find a cheap/used Mini-ITX DC-DC PSU; if I find a 12V one, is there any way I can use the above mentioned brick with that? Resistors?

* I read somewhere someone used a PSU from an old discarded external drive cabinet to power a system. There's no way to pull 12, 5 and 3.3 volts out of a PSU like that? I guess that could be a cheap way to get 12V to the mITX PSU above though?

Any suggestions?

Kent

BillyBuerger
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Post by BillyBuerger » Tue Mar 18, 2008 12:31 pm

I would probably guess closer to 50% efficient at that low of a load. But even really efficient PSUs aren't going to be very efficient at that low of a load. And even if something was 80% efficient, you're still only talking a couple of watts. So maybe 20W instead of 22W. It seems overkill to me to worry about that. Especially if you don't have much money to spend.

Your brick with a Pico-PSU type thing would be your best bet for efficiency. They make models that accept from 12-32V or so that would work with your brick. But they generally aren't cheap that I've seen.

The FSP Green 300W is my favorite cheap, low powered, efficient PSU.

I too am using an old HP microATX board with a 600Mhz Celeron for a server. It's my file/web/mysql server though. It runs extremely cool although I don't have a watt-meter to test what the actual output is.

kentc
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Location: Gothenburg, Sweden

Post by kentc » Tue Mar 18, 2008 12:43 pm

BillyBuerger wrote:I would probably guess closer to 50% efficient at that low of a load. But even really efficient PSUs aren't going to be very efficient at that low of a load. And even if something was 80% efficient, you're still only talking a couple of watts. So maybe 20W instead of 22W. It seems overkill to me to worry about that. Especially if you don't have much money to spend.
Yes I know, although with the firewall running 24/7 the watts stack up.. Also it's the question of estetics. My idea is to mount the motherboard displayed on the wall with a piece of plastic covering it. A traditional ATX PSU will look kind of bulky on the wall :)

Another idea that I've kind of almost discarded myself is to dig through the basement and find a 3.3v, a 5v and a 12v power adapter and run it of three different adapters :)

drees
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Post by drees » Tue Mar 18, 2008 1:00 pm

A PicoPSU with a wide input range would be your cheapest overall solution ($50-60) and offer very good efficiency as long as your existing brick is efficient.

Just keep in mind that the PicoPSUs with the wide input range are slightly less efficient than the models which pass 12V straight through since it also has to regulate the 12v line, but either will be vastly better than your current setup.

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