[time-nuts] Modern motherboard with RS232 port

Ed Palmer ed_palmer at sasktel.net
Sun Aug 19 20:51:47 UTC 2012

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.


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:ed_palmer at sasktel.net
>>> To:time-nuts at febo.com
>>> 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<stanw1le at verizon.net>  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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