I normally wouldn't ask such a question in here but I know there's a
lot of good electrical people here who'll hopefully know the answer.
I'm trying to work out exactly how much it costs in electricity to
have 2 PCs running all the time - a webserver and my development
Both are AMD Athlons with 350W power supplies running the motherboard,
half a gig of ram, 2 SCSI disks and 1 or 2 case fans for cooling. I
know I'm not running the PSUs to full capacity so is there a way of
working out the consumption?
Oh, the webserver's monitor is pretty much always off and when I'm not
using the development machine the monitor is either off or in standby
mode, dunno if that makes a difference :)
kW * hours = units: price per unit is on your 'leccy bill.
The actual power consumed will be less than the power supply rating but
it'll get you close enough for Jazz. Add the rating of your monitors.
Maria and Marlon say "I can't believe it's not butter!"
On occasions when I want to "size" consumption of computer equipment
(typically for working out what capacity UPS is required), I tend to use
a clamp meter and a specially made up short extension lead. The lead has
a couple of meters of the outer insulation stripped off. Hook whatever
you want to measure up to the lead, and then clip the clamp meter round
the live conductor. That should give you the current draw. Multiply by
240 to get a VA rating, and finally (in the case of computer equipment)
multiply the result by an estimated power factor of 0.8 to give watts.
For small loads like PCs I tend to coil up a section of live conductor
and put the clamp meter round ten turns of it, then divide the result
read from the meter by ten. This gives a more accurate result.
A few months ago I replaced my ancient 75 MHz Pentium system with a shiny
new 2.8 GHz P4 - Dell Dimension 4600 with 250 W PSU. With the machine
running continuously there was a noticeable increase in electricity
consumption. Out of interest I took the following measurements:
Power Current Earth
Equipment /W /A VA PF /uA
-------------------------------- ----- ------- ----- ---- -----
Old sys unit (P75) idle 30 0.185 44.4 0.68 30
Old sys unit (P75) CPU 100% 39 0.233 55.9 0.70 30
Iiyama 17in. CRT monitor 90 0.566 135.8 0.66 60
New sys unit (P4/2.8GHz) idle 100 0.505 121.2 0.83 30
New sys unit (P4/2.8GHz) CPU 100% 155 0.800 192.0 0.81 30
Dell 18 in. TFT monitor 42 0.268 64.3 0.65 40
PSU for computer speakers 4 0.048 11.5 0.35 -
HP LaserJet 4 printer (warm up) 790 3.300 792.0 1.00 140
HP LaserJet 4 printer (standby) 35 0.239 57.4 0.61 140
Power measurements taken with a Feedback Instruments wattmeter.
Current figures are true RMS, taken with a Fluke 87.
VA figures are apparent power, calculated assuming Uo = 240 V (i.e. the
approximate actual supply voltage, rather than the nominal 230 V).
'PF' column is power factor (W / VA).
'Earth' column shows protective conductor current (in microamps) taken on a
Fluke 77 (mean responding). Note that the measured figures are far less
than is commonly assumed in threads about spurious RCD trips.
Figures for the monitors were with 'typical screens', not max. brightness &
'CPU 100%' figures taken with the SETI at home client running.
You could happily put allthat kit *except* the laser printer on an 800VA
UPS, yes. *Don't* put laser printers (inkjets are fine) on "domestic
sized" UPSen - as the figures show, when the heater for the laser printer
kicks in (to fuse the ink to the paper) it draws a much bigger peak than
most under-desk UPSes will cope with; you'll end up shutting down everything
on the UPS, and maybe blowing its own overcurrent protection (most usually
UPS sizing is a victim of market-speak specmanship, BTW: an "800VA" UPS
will typically supply that power for only 5 minutes or so once disconnected
from mains input. (Check out individual manufacturers' websites for
full details). If you want, say, 15 minutes' runtime, you need to
"oversize" the UPS, i.e. get one with bigger batteries. Some mid-range
and upwards models allow you to add extra batteries to increase the
time of independent working, rather than the peak output. The excuse for
the "5 minute" rating is that that's long enough for the automated orderly
shutdown procedure, or to provide continuity until a dedicated backup
generator kicks in. For a single webserver, running headless or with the
screen pulling very little power in its standby mode, you'd probably get
30+ minutes of autonomous running out of an 800VA UPS; but again, you'd
need to check manufacturer's specs before you buy. UPSes made by APC -
and for all I know those made by other makers too - come with a
"calibration" function where you can run the UPS down to "near-empty" with
the particular load you run, allowing the monitoring software to know
how many minutes the batteries are good for with your particular load.
HTH - Stefek
On 22 Sep 2003 09:10:23 GMT, email@example.com wrote:
Be aware that if using the calibration function the UPS may well
shutdown at the end of the cycle even though it has mains input. This
may be related the the various settings probably the interrelated,
shutdown on low battery, restart time or restart after x percentage
recharge. BTDTGTTS. B-)
Dave. pam is missing e-mail
On 22 Sep 2003 09:10:23 GMT, firstname.lastname@example.org wrote:
Yeah, I'd only be powering the 2 base units, one 19" monitor and the
router; the rest can die. All I'm bothered about is shutting the
webserver down if the brownout's going to be longer than 5 or so
minutes 'cos if it IS that long then it wasn't my fault :o)
I have, OS/2 or Linux. Just haven't got round to finishing the client
that will talk to OS/2 box for the linux boxen. With only one cut
every year on average it's hardly worth the agro and the Linux box
appears to survive not being shut down properly anyway.
One day the UPS comms will be plugged into a linux box and then I
might get the others to shutdown properly as well. Of course there is
the added problem that even if shutdown they remain on (old machines)
so I need a hardware solution for that and the newer machines don't
power back up when the power comes back without a physical prod of the
power button. Yes, I have tried the various options in the BIOS to no
Dave. pam is missing e-mail
I use Solaris x86 (not surprisingly), and with journalling filesystem,
I've never had any problems with power cuts and no UPS. Funny enough,
there seem to have been 4 power cuts yesterday. Prior to that, the
systems had been up for around 170 days since previous power cut,
which IIRC, was also last of a several power cuts over an hour or so.
I think you don't normally bother powering the systems off. You would
program the UPS to shut the system down when UPS has less than, say,
2 minutes left, and the UPS itself shuts down some 2 minutes later.
When power comes back, everything comes back on as it was switched
on when power went off (ATX systems should remember this, although
since none of my systems are newer than P120's things may have changed).
However, UPS software is notoriously crap, and it's not at all
uncommon for it to be responsible for more downtime than power cuts
are. When I setup some commercial servers, I eventually stopped
using it (except for monitoring the UPS) -- system availability was
much improved just by letting the UPS kill the power to the running
systems when battery went flat. In your scenario, if the mains power
comes back on after UPS has told systems to shutdown but before its
own battery went flat, what causes systems to reboot?
On 23 Sep 2003 08:39:37 GMT, Andrew Gabriel wrote:
My ATX boxen don't, the good old 486 and P133 do. On the 486/P133 the
power switch is a real power switch in mains lead when power returns
up comes the PC. The perishing ATX boxes have a "soft" power switch I
have yet to find away of getting them to power back up on a return of
mains. There is a BIOS setting but it doesn't appear to have any
effect, I suspect something has to be set during the shutdown
sequence. When running doze and you shutdown the box switches "off"
with Linux or OS/2 it doesn't.
The OS/2 stuff from APC isn't particulary good or wasn't 4 years ago.
A friend wrote a far better bit of software which I use.
ISTR that there is a bit of dialogue between the UPS and the PC
software. The UPS tells the PC of its status, on mains, on battery,
battery low etc and the PC software acts on that information. If a
shutdown is started it tells the UPS to switch off after a delay. The
UPS will then go through it's programmed startup routine, I think,
I've never really played with it as I'm normally here and it's no
great shakes if stuff doesn't come back up automagically anyway but it
would be nice.
Dave. pam is missing e-mail
ATX systems are supposed to save the soft power state to NVRAM
and if mains goes off/on again, return to same state. So if system
was running before power cut, it should reboot, whereas if system
was soft powered off, it should stay that way (you may notice it
come on for a split second whilst it reads the NVRAM). Some systems
may have BIOS settings or ACPI functions to override this behaviour.
The ability for the OS to soft power down a PC requires it to be
able to understand the BIOS ACPI function, developed mainly by
Microsoft with the apparent intention that no one else would be able
to make head nor tail of it, which is why it often doesn't work when
using other operating systems. Prior to that, motherboards supported
a sequence of some bytes which when written to an i/o address in the
right order and relatively quickly, would trigger the soft powerdown,
although the sequences varied between motherboards.
APC for Unix had various faults -- leaked memory until the system
ran out and hung (HP-UX), after a few weeks it would get stuck in
a 100% CPU loop arguing with the serial port driver (Solaris and
HP-UX), and it was responsible for a number of security alerts.
On an associated subject I had to measure the quiescent power/current
the whole house recently, with "everything off" - which still leaves 2
fridges, a freezer,
various tv/ video, computer / hub, modem etc etc on standby and the result
400 watts, averaged over some 6 hours of sleep time - meter readings at
06.00 hrs on several days. I couldn't believe it so I bought and fitted
an additional electricity meter which confirmed it - the elec. board changed
about six months ago and that also gives the same results.....
I am now setting about fitting the second meter into each of the MCB
circuits to find
out where all this is being used - its about 9 units a day which is some 40%
daily consumption of about 23 units/day
Anyone else looked at this - is this normal ??
I fail to understand your surprise. You have two fridges and a freezer as
part of your "everything off" load, right? Even the "A"-rated fridges
eat about 1kWh per day (the Euro Standard rating system seems to be to give
kWh per year, with common figures around 300-400). So that's 1kWh in 25
hours (we round upwards for ease of calculation ;-) meaning 40W for a
single, energy-efficient fridge. Multiply by three and fudge in a bit more
for the age of your fridges and we've got 200W at least. Add on your
kit on standby, maybe a CH boiler and pump, any "security" lights being
turned on by foxes at 3 a.m., and a 400W draw seems unremarkable.
Rather than messing about with:
why don't you just unplug one of your fridges/freezers each night for a
few nights and watch the effect on your overall consumption? (They have
good enough insulation that 6 hours without power won't turn them into
a soggy salmonella-breeding mess... at least one hopes so!) And repeat
that procedure for your other circuits - if you're that keen, you can
work at the whole-MCB-circuit level first, then delve deeper into
individual bits of kit which are on the higher-background-consumption
circuits. But it does seem to me that the figures you give are nothing
remarkable. If you want to cut down consumption, look into consolidating
your chilled food storage, maybe into a new energy-efficient thing if
your existing ones are old (you get better efficiency overall from one
fuller fridge than two mostly empty ones!), use compact-flourescent
bulbs, turn anything which you can (teli, 'puter - it's got a battery
for its realtime clock, dammit) right off rather than leaving it on
standby. To draw in another thread, a UPS can be a useful single-point
of power control for all your computer kit (if need be you plug in
a couple of 4-way extension strips into it); or at less cost, wire some
4-way extension strips into one of those 4-way plugs, or do *one* step
of daisy-chaining from a "master" strip into subsidiary ones, to give you
a single place where you can turn off *all* your 'puter kit. But do
*measure* where your "background" power is going before putting in lots
of effort into a minor contributor; I suspect the bulk of your baseload
consumption is from those fridges and freezers.
HTH - Stefek
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