Archive for power consumption

Power consumption update

I’ve done some testing using an inline power monitor of the power consumption of my home server. Originally I just wanted to get an idea of how much power my server was using (and hence how much it would cost to run it) but testing power consumption becomes addictive – now I just can’t stop.

Results from my original measurements;

Each 250GB SATA hard disk            = 9W
Hauppauge TV tuner card               = 5.5W
PCI SATA card                                 = 2.5W
Motherboard and CPU                     = 39.5W
TOTAL Power consumption at idle  = 65.5W (with X-power CPU)

UPDATE 1: TOTAL Power consumption with Silverstone PSU = 72W
UPDATE 2: UPS power consumption = 9.5W
UPDATE 3: 3com Network Switch power consumption = 17W
UPDATE 4: Cisco 3508 & 3524 switches both = 50W

UPDATE 1: TOTAL Power consumption with Silverstone PSU = 72W
These tests were done with an old X-Power ATX 400TD power supply that I had spare – I found this a bit noisy so I swapped it out for a really really quiet 400W Silverstone PSU (ENH-0140G-XA) that I had – the Silverstone PSU only has a 20pin ATX connector (and the motherboard has a 24pin one) but the manual says that either a 20 or a 24pin PSU will work. I was shocked to find that the power consumption went up to 72W. just by changing the power supply the power consumption has gone up 7.5W – nearly as much as adding an extra harddisk – an extra 11.5%.

Put it this way if I assume that the X-power PSU is 80% efficient then the silverstone PSU is only 72.5% efficient. That’s an enormous difference – perhpas it’s due to only having a 20pin connector and not powering the other 4 pins. Anyway I guess my next purchase is a super silent PSU with 24pin ATX2.0 connector. OR maybe I’ll go back to the old X-power CPU – it it really is a bit noisy but the machine is kept in the cellar so it should be OK.

I can only think that although the Silverstone CPU is a better ‘brand’ and quieter it’s just not as efficient – chosing the right PSU has just got more complicated!!

UPDATE 2: UPS power consumption
I’ve salvaged an old UPS that had been left for dead. But when I connected up the server powered via the UPS I found that the power consumption had increased dramatically. Adding the UPS increased the power consumption by 9.5W.

UPDATE 3: Network hub/switch
The full power consumption of the whole network at idle includes the power consumed by the hub which has to stay on all the time of course. The gigabit hub which I have is a pretty basic unmanaged affair (a 3com baseline 2824). At idle with no traffic it consumes 17W.

UPDATE 4: Cisco 3508 and 3524 switches
Crikey! near enough 50W for these switches (each!). I wanted to move to a cisco setup since I had suspicions about the 3com switches and sunrays. BUT I’ve contrived to need both switches instead of just one since the 3508 can’t negotiate 10/100 base and the 3524 doesn’t have enough gbit ports. So if I commit to this I’ll increase power consumption from 17W to nearly 100W.

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Salvaging an old UPS

Ages ago I was given an APC PowerStack 450 UPS that was apparently dead. Being an eternal optimist I decided to see if I could resurect it. In theory no mater how knackered the batteries it should function when the mains power is on but crucially if no batteries are inserted (or if the batteries are in fact so dead that they conduct no current) the device is a brick. My hope was that it had been in storage for so long that the batteries had sulphated to such a point that they no longer conducted.
First I got the multimeter out and checked what I could (the internal fuses etc.) and it all seemed OK but the battery seemed lifeless even after charging with an external charger.

Before commiting to new batteries I wanted to test the device so I found some 6V batteries (that wouldn’t physically fit) and jury rigged connections to the device – blimey it works!

So now to get some new batteries. These cost a fortune if you buy the APC branded ones and even OEM ones seem expensive for the size of battery. I worked out that the batteries in the Powerstack 450 (APC part RBC18) are infact two CSB GP672F2. I found these available from the main reseller for CSB in the UK, MDS, and bought two batteries for £23.98 – a considerable saving over the APC part.

I striped down the old battery packand reassembled a new one using the replacement batteries….

Well it works!
The first thing that I noticed is how much power it consumes – I did some simple testing of power consumption on my server previously and I’d left the power monitor plugged in. Without the UPS the server consumes about 72W but with the UPS inline the whole setup consumes 81.5W – I didn’t realize how much power a UPS would consume in it’s own right!

As an aside I’ve created an updated page about power consumption of components and systems here.

To control the server and allow for a gracefull shutdown in the event of a power failure I decided to install the apcupsd (originally I tried NUT – network UPS tools – whoa way too complicated). I found the correct wiring for making up a serial cable to connect the UPS to the server.


INSTALL apcupsd

#yum install apcupsd apcupsd-cgi

That just seems to work…

Then I set up apcups by simply following the apcupsd documentation.

GOTCHA - problem with Xen stealing the serial port! Work around from here.

Now it seems to work and the status page is here...

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LINUX HOME SERVER – power consumption measurements

With the set-up of my LINUX HOME SERVER I choose components in the hope to minimise the power consumption (at the obvious expense of performance) of the system. The cost of electricity isn’t going down and I wanted to try and avoid an enormous bill each year just for having the server idel for long periods of time. As well as choosing power saving components I disabled anything in the BIOS that wasn’t going to be used (e.g sound, serial and parallel devices) in an attempt to reduce power consumption still further.

First I made a sort of back of the envelope calculation at what the maximum power consumption should be;
31W CPU (published TDP of the chip)
25W Motherboard/chipset (can’t remember where I saw this! – oh yes here…
4W System disk
16W 2x Storage disks
104W Allowing for PSU 75% efficiency

That’s my target but I don’t have to guess because I borrowed a plug-in energy monitor that tells me the power consumption of any appliance.

So what the verdict?   Actually when I booted the machine for the first time the power consumption spiked at 105W (blimey that’s uncanny!) for a second or so then subsided to a steady 60W when the machine is totally idle (just sitting at the login screen). I should note that the server used 4W when turned off.

I wanted to dig a bit deeper and estimate the contribution of individual components the overall idle power consumption. so I started to systematically remove all the components I could
1. Turned off – 4W
2. Maximum recorded – 105W 
3. At Idle – 60W
4. As 3 but with the two storage disk removed – 42W
5. As 4 but with the ICYDOCK cage unplugged – 42W
6. As 5 but with the PCI SATA card removed –  39.5W*
7. As 6 but with a Hauppauge Nova-T tuner card installed  – 44.5W*
8. As 3 but with a Hauppauge Nova-T tuner card installed  –  65.5W*
The only other things I could unplug would be the cooling fans and I didn’t fancy doing that. 

*The meter measures to the nearest Watt – but in some readings the value oscillated up and down by 1W.

Overall I guess I’m pretty happy with 60W at idle. I saw a review of Windows Home Server Machines where they measured power consumption and it’s pretty comparable (the range was 40 to 55W) if a little on the high side. This is acceptable considering my server is a much more capable machine that the average WHS offering. I guess the most striking results are;
— Just how much power Hard Drives consume…my estimate is that each drive uses 9W of power just sitting idle.
— Having a PCI card sitting in the machine that I’m not using (the Hauppauge card) is undoing alot of savings made elsewhere – the card uses about 5 or 6W of power and is just sitting there doing nothing at the moment.
— Although not all PCI cards are the same (obvious I guess) they all consume a few Watts – the PCI SATA card is estimated to use about 2.5W while the PCI DVB-T tuner card about 5/6W. It occurs to me that a PCI-express based card (which operate at lower voltages) should consume less power – it would be interesting to do a comparison using a Sil3114 PCI-e card (if such a thing exists) or a PCI-e based TV tuner.

Cost implications…
Well if it runs 24 hours a day at 60W (idle) then my bill will be increased by about £65.

I’ve based this on my simple calculation;
0.06Kw * 24 = 1.44 kWh (kiloWatt Hour) per day
1.44 * 365 = 525.60 Total kWh per year
£0.1236  * = £64.96 Total cost of running the computer

Next steps….
I guess I must see if I can make use of the mobile style power saving capabilities of the setup yet more by using power management to power down most if not all of the system if it sits idel for long periods of time. I guess the obvious place to start is with the hard disks since they use so much juice.

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