Archive for October, 2008

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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