Green PSU

[speardane]

I want to build a pair of servers.

1 as a router - probably using clark connect or similar - low spec - 1 small disk
1 to run MythTV (backend) & slimserver & hold all the backups.

primarily I'd like them to be quiet & low energy. Possibly

• a dedicated low power computer like the Soekris looks neat & tempting - but relatively expensive, if you have many spares...
• and for the media server a small NAS, that could have additional sw installed, would seem low power & relatively quiet.

I am tempted (as usual) to go for the control & flexibility of building my own.

• bar the case, PSU & disks I have most of the bits to hand.
• I'll probably rack mount them (I've found some cheap 4u cases at ebuyer)

I've been researching PSU's and found the limits of my ignorance... I am not sure exactly what the power & efficiency ratings really mean in a computer system context.

suppose I install a 500w 80% efficient PSU in a system that only needs 200w (at a particular time)

• does this mean that only 250w is used?
• (ie 200= 80% of 250w).
• or would it consume 500+w whatever it was doing?

I'd also be interested to find an outline of the relative consumption of CPUs MBs etc. I have found commercial calculators on the forum - but really I'd like to be pointed to an articulate explanation.

[Giraffe]

It will use what it needs.
I have a 330W PSU and most of the time it's at about 45W (input, so only about 30W output). Bear in mind that most 80%+ PSUs don't reach that level until about 20%+ output. Mine's running at about 15% output - I've allowed a bit for that in the above figures.
No harm in having a bit in hand; I've seen about 90W input when using CPU, HDD and burning a disc. I just got the smallest, standard ATX, good quality PSU that Scan had (Seasonic S12).

[kmac]

The efficiency quoted is usually the highest efficiency achieved.

This is not achieved at all loads - there is usually a bell like curve where the efficiency is lower at low loads and near max load and seems to peak somewhere near the middle.

So you are correct in your example that a 500W PSU, if only 200W is need will probably draw around 250W if it is 80% efficient, but it may draw a little more as 80% is probably the highest achievable efficiency if it is quoted.

See this article which shows efficiency measurements acorss different loads

Modu82+ 625 Power Supply: Enermax to the Forefront | silentpcreview.com

The site is a useful resoruce if looking for an efficient low noise PSU

The Enermax Modu82+ 625W PSU comes tops but there is also 525W and 425W PSUs in the range - quiet and good quality

[kmac]

Power Supply Fundamentals | silentpcreview.com

Above is a good guide to real system power consumption....

[arthurleung]

I would suggest you combine the two systems as one? Router use pretty little CPU and it would be a waste of power over a single-system setup.

I would recommend getting the Seasonic S12 380W for maximum efficiency (~85&#37.
There is not much point in getting a 4U case as you have nowhere near that much stuff to put into the case (e.g. a dozen of hdds). It would be easier to maintainance if you have a small and light case like a shuttle (or any other cube case).

A typical A64 / C2D system that will handle your need at about 120W (from socket) without fancy graphic cards.

[amdavies]

Is anyone aware of any place in the UK doing 200-250W 80plus rated PSUs ? I know SPI has a 250W version but I've been unable to locate it here.

With the rising cost of electricity and the government's pushing of using less energy, I would have thought that low power, high efficiency, PSUs would be much more prevalent.

[staffsMike]

Is anyone aware of any place in the UK doing 200-250W 80plus rated PSUs ? I know SPI has a 250W version but I've been unable to locate it here.

With the rising cost of electricity and the government's pushing of using less energy, I would have thought that low power, high efficiency, PSUs would be much more prevalent.

But the point of a high efficency PSU means that it wouldn't matter what it's max output was but how efficiently it can operate on low power demands.

I mean most people with a decent 500w PSU are probably only using 250W on a midrange PC or 350W on a high spec graphics and overclock system.

[Giraffe]

PSUs of that wattage will tend to be non-ATX, meant for small cases (so short leads). Seasonic do some (but are they available in the UK?) but the only one that I saw of 80% was 300W, so unless you're short of space the standard ATX would be easier and cheaper.
From SPCR's site (kmac's link above), Seasonic actually have a flatter efficiency curve than most, so pulling 50W from a 330W PSU will make v. little difference. The PF is also close to unity and that minimises VA load and heat.

Another factor: even if the PSU is a bit OTT, it'll last 'for ever', so the environmantal costs of replacement will be avoided.

[speardane]

Thanks!

I was considering corsair PSU's on the grounds of their long warranty (5 years) . I recently had what I thought was meant to be a fairly high end PSU (Zalman) fail at the worst possible time. I didn't lose more than about 15minutes worth of data - but I did lose about 3 hours (fix & recovery time) when I had a really tight deadline.

2 reasons for splitting the servers. Security separating data in the DMZ from internal data + booting from a CD/DVD into memory for the router. Power usage - powering down all the disks (if not the whole system) at low usage times eg overnight.

I need to go research how different MBs & OS cater for powering down - very much inclined to go linux probably Hardy - Ubuntu when it's out in a few weeks...