I was afraid that this topic would turn into a swamp and I didn't help
things by getting it backwards. Yes, the residential meter measures
WattHours, not VoltAmpHours. My apologies for adding confusion to an
already confusing topic.
While new PCs may have power factor corrected power supplies, many of us
at least consider reusing old PCs. The differences between watts and
volt-amps are significant on these machines.
I powered up an old Compaq 1 GHz P3 and found that it draws ~60 watts
and ~92 VA. Both are much lower than the stated draw of 4 amps @ 110
V. It actually draws ~0.75A.
My main computer is a Dell Precision 490 Workstation. It draws ~180W
and ~180 VA so it has power factor correction. But the stated rating is
6 amps @ 110V while it only draws ~1.5 amps.
Any difference between Watts and VoltAmps can become an issue when you
deal with a UPS (Uninterruptible Power Supply). I would hope that an
NTP server would be plugged into a UPS. Most UPSs have different
ratings for Watts and VoltAmps. You need an accurate measurement of
your load to size the UPS correctly.
So my basic point is still valid. For computers, don't believe the
values stated on the labels. Measure them first.
Ed
On 8/19/2012 1:38 PM, Christopher Brown wrote:
IIRC...
VA for AC is peak volts times amps, not RMS volts. The whole point of
dealing with RMS being that it makes AC and DC equiv for purposes of V *
A = W.
Converting VA to W is same as converting peak V to RMS V.
Though I am a little surprised about residential power being
measured/billed in VA not KW/h in North America. Pretty sure the US is
in North America, even Alaska in slightly more North America. Never
seen a VA/h meter in the US.
Was guessing it was a CA thing, even though I had never run across any
mention of VA billing in CA, but am looking at Manitoba Hydro, NB power
and SaskPower billing rates right now in KW/h.
Ed, can you chime in here, where is power billed by VA (outside of some
commercial/industrial and private generation agreements)?
VA is used all over the place in electrical systems calculations and
equipment specs but have never seen billing on it.
On 8/19/12 11:19 AM, Tom Knox wrote:
Hi Ed;
I may not have had enough coffee yet, but if Volt X Amps = Watts why would
there be a difference?
Best Wishes;
Thomas Knox
Date: Sun, 19 Aug 2012 12:35:51 -0600
From:[email protected]
To:[email protected]
Subject: Re: [time-nuts] Modern motherboard with RS232 port
It's important to remember that on a computer, the wattage shown has no
relationship to the wattage pulled from the socket. The numbers shown
are maximum values. You have to measure the power draw and you have to
measure it in volt-amps, not watts because that's how residential power
is measured (at least in North America). Buy an energy meter that shows
volt-amps. They're relatively cheap - typically less than $50.
Ed
On 8/19/2012 11:06 AM, Chris Albertson wrote:
This sounds like a newer version of the board I use. The thing to check
is if the CPU heat sink has a fan or not. Having no fan indicates that the
CPU is not using much power. It also removes a common failure point.
To reduce power even more. On an NTP server you can unplug the keyboard,
mouse and monitor and if you have other servers on the LAN configure one as
a "boot server" and have it run TFTP then your NTP server does not need a
disk drive. It can run off a "RAM disk". This makes it very fast, even
faster than a SSD and it saves some cash. Makes backup easy too as there
is nothing to backup if there is no local storage. If you don't have a
TFTP server use a small notebook size disk drive. Even a 80GB drive is
overkill. You can also boot from a USB thumb drive and run a RAM disk.
It is worth it to look at your electric bill to find how much you pay for
power. Here I'm at $0.21 per KWH. A full size PC server can use 250W or
more. There are 8760 hours in a year so you get $460 per year to run that
250W PC. The little Atom will pay for itself in just a few months. The
first time I did that calculation, my "power hogs" where given away.
On Sun, Aug 19, 2012 at 7:42 AM, Stan, W1LE<[email protected]> wrote:
Hello The Net,
For your consideration:
The INTEL model DN2800mt ITX mother board uses a ATOM CPU and
draws about 11 watts of AC power when configured as:
(I have not measured DC power yet.)
30 GB OCZ Nocti mSATA solid state drive,
WIN7 pro, 64 bit, USB keyboard and mouse
APEX MI-0008 case.
Also has:
parallel port available on mother board, you extend to a connector
RS232 serial port available on mother board, you extend to a connector
a single DC power supply from 11 to 19 V DC.
1 each PCIe expansion port, I will use with a premium 4 channel sound card
SATA ports available for HDD/SDD,
USB ports are available,
Motherboard sound, and Gigalan.
I have not played with NTP, (yet), but it sounds like a decent time nut
technical challenge.
My application is for a remote site with only 13V DC power available from
PV/batteries.
Then use fiber ethernet to get off site.
The INTEL website would have further details.
Stan, W1LE Cape Cod FN41sr
ZZZZz
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