[nmglug] Spare P2s all running from one big power supply and irritating Flash Player

[WA7BSZ]

Well, there are a couple things that might happen.

Sometimes the motherboards like to be grounded to the cases, and may
not work well without thaty connection.  However, some other
motherboards do better if they are not connected to the case in
multiple places.  One of those EMI conditions that is sometimes better
one way and sometimes better another.

Another issue is that your power supply connection will be higher
impedance, and noise from one board will show up on the power supply of
the others.  So, it might work ok to use one big power supply if you
hvae nice large conductors going to each motherboard so there isn't too
much power conductor impedance.  It might not be a problem, but it just
seems like there might be a power line noise/voltge drop problem if you
have to put many extender power supply cables in to power all the
boards.  How would you do this anyway?  Usually there is only one power
connector set coming out of a power supply.  Plug it into one board and
you are done.  You could perhaps find a source of those connectors and
make some multi-connector cables.  

The more I think about it, It would be a problem.  The computer talks
back to the power supply, so if you put more than one motherboard on a
power supply there would be the equivalent of bus-contention.  If there
were two output lines on the same wire, and one says "its a one" and
the other says "its a zero" then one of them might get burned out.  

So, to do that you would probably have to get a bundh of connectors,
make your own extra cables, and figure out all the signals and how to
plug them in together without anything burning out.  Maybe you would
hve to make a little extra circuitry so they could all exist
peacefully.  

In order for the P2 to be able to shut down controlled by software, it
has to have some control lines that control the power supply, so it can
shut the computer off and even wake-on-lan.  That circuitry expects
just one master.  If you understood the signaling, maybe you would just
have one motherboard be the master, and leave that line out on the
other motherboards.  

That would be a project in itself.  It could probably be done.

Let me talk a little on this rating of these power supplies.  Their
ratings must be for how much power they could deliver for about one
minute before smoking furiously.  See, they tell you that you need a
350W power supply, but the actual power they use is maybe 120W.  That
is for a pretty hot computer.  If your computer was really using 350
watts, that would be like having a small heater on all the time.  If
you had three computers on at the same time all taking 350W, that is
like having a little kilowatt heater on all the time.  Just fo get your
electric space heater, say a 600W unit, and put that in your 8' x 10'
computer room, and turn it on all day and all night, especially in
August, and see what just 2 computers dissipating 350W each would
actually do to the room temperature.  

My 350W supply computer actually draws about .8A or less (I have a
little current meter).  So, I have to have a 350W rated supply so that
the computer has good voltage to give to the processor regulator and
other circuits on the motherboard, so that there aren't any voltage
dips that cause data problems and cause the computer to lose its mind. 
But the power supply is usually delivering and dissipating about 100W
or less.  

So, if you need say, a 250W supply for each motherboard, and you have
8, then you should get a power supply rated for 2000W.  (Might need 220
for that).  Not because it really needs to supply 2000W, but because
motherboards are sensitive to some slight variations in their input
voltages, so they need to over rate the supplies so that they provide
the voltages in a more stable manner.  Or maybe their stated wattage is
a selling point.  You don't really get a 350 Watt supply when you buy a
350W supply.  Maybe it is like Magahertz and Gigahertz.  The more the
better, even if it makes little difference really, because hard drives
still are not much faster than they were 5 years ago.  

Anyway, it looks like a project that has a chance of some unexpected
problems in getting all the power at the correct source impedance to
all the motherboards.  Just thinking out loud.

Well, you would need to know how much power the CDs and hard drives
take.  Probably a hard drive takes maybe 5 to 10 Watts.  So you might
save 50W taking out the drives.  The CDs don't take much while idle.  

I think it would be pushing it to get two motherboards operating from
one supply.  I believe you would have to make up your own special
connectors and patch cords and solve the signal problems.

My estimate of how much power 8 P2s would probably take.  Well, if they
actually only take about 60W each, that would be about 500W, only one
monitor used.  500W for a month is about 360 KWH. If it was 8 cents a
KWH, that would be about $30.  If it really did take 2000W, that would
be $120 a month if you kept it on all the time, plus, if you have an
air conditioner, you would be paying more to cool the area (probably
not in the garage).  If you could get the air into the house in the
winter you could use the heat from the power you are paying for.  

To figure out what one computer uses for power?  If you had an AC
current meter you could get a worst case estimate.  Find the current,
and this would be a average over time, and multiply that times your
voltge which is probably about 118V.  As the computer does different
things it takes different amounts of current.  On my meter it might go
up to 1.1A for a second or two, then back down to .6A or so.  Now if I
had it calculating some weather program, then it would go up to the
1.1A all the time and I might want to put a few more fans in it.  So,
for calculation intensive, always on situation, it would be dissipating
about 130W.  This is a 2GHz processor machine, and your 400 MHz guys
would be lower power.  130W for a month at 8 cents/KWH would be 94 KWH
a month and about $7.50 for the electricity.  This estimate might be a
little high because of power factor, the current might not be in phase
with the voltage or the current may be in pulses, not sine waves.  

Now I am curious to see if there is a good way to figure this out
without true RMS power meters.  If you have a lot of the same computer,
like you do, you could probably get a good estimate by turning them all
on and everything else in the house off, and see how fast the meter
spins.  Then shut off everything except the dryer, and see how fast it
spins for that, assuming you know what current that is drawing at what
voltage.  You might get 10% accuracy, I don't know.  A power meter
reads differently than a current meter.  

A way I would trust to figure the RMS power being taken by a computer
would be to get a 1% tolerance 1 ohm resistor, and put it in series
with the neutral side of the power going into the computer, then read
the voltage across it with a scope.  With a dual trace scope you could
see the voltage and the current and the waveform of the current, and
you could hopefully calculate the RMS power the computer is taking. 
Make the computer do calculations.  Run Spice simulations that take 2
days while taking the measurement.  Then you would hvae a good estimate
of the power one computer takes while calculating.  

Computers take a lot different amounts of power depending on what they
are doing.  Sitting idle, they are at low power.  Boy, go to the wrong
websites with their flash presentations and you will have 100%
processor usage and will be drawing the current.  How about that? 
Flash Player might be increasing the power used by computers by 100%,
and that is a lot of money considering all computers.  This happens, as
I watch the computer processor usage, and on the wrong sites the little
flashplayer advertisements sometimes really get going.  So then, you
might be paying $5 a month for flash advertising.  A company with 1000
computers might be paying $5000 a month or more for flash advertising,
if people surf to the sites and leave their browsers up on those sites
all night too.  How interesting.  (Kind of like getting junk mail on
your fax, you have to pay for the paper to get the ad you don't want.)
Even Yahoo.com has flashplayer ads.  The faster your processor, the
more power it will use on flash player, showing you those cure little
irritating animated ads that you can't shut off.  You can go to lower
quality, you can zoom in.  You can click on the play control, but it
keeps playing anyway.  "Sorry buddy, we paid for this ad, and its going
to play on your computer, so get used to it."  That is why I don't
install flash player.  It comes on some distros, so I have it to some
extent, but I don't like it much.

One of my computers was running pretty slow, slow response to user
requests, so I looked at the processo usage, and it was up around 95%
most the time (from top command).  I found one website that seemed to
hve a lot of flash (this was on a distro with flash already installed,
Xandros I believe) and I shut off that window, and viola, 50% processor
usage.  Then I found another couple flash sites, and killed them and
then the processor was at 20%.  It responded a lot better.  So flash
player can be a real processor hog, and it is on a lot of tech sites
heavily.

Anyway, I would say just use one supply per motherboard, and 8 400 MHz
computers on all the time and calculating all the time might cost $30 a
month for electricity if they only take a combined 500W. If they take a
combined KW, it will be $60/month.  

I wonder if anyone will read all that.  It is a lot. 






>    Spare P2's and boinc 
> 
> 
>
----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 8 Mar 2005 19:35:55 -0800 (PST)
> From: Tim Emerick <timothyemerick at yahoo.com>
> Subject: [nmglug] Spare P2's and boinc
> To: nmlug nmlug <nmlug at nmlug.org>, nmglug at nmglug.org
> Message-ID: <20050309033555.51348.qmail at web40912.mail.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
> 
> I have about 8 p2-400's that I'm looking to turn into some sort of
> project. 
> I was going to try to do a LTSP type project but never got around to
> it.  Now
> I've decided I want to set them up in the garage to crunch boinc/seti
> stuff. 
> Couple of questions for the knowledgeable ones.
> 
> 1. I'm curious about clustering.  Would there be much of a
> performance gain
> by clustering them together in order to run BOINC or just run them
> individually.
> 
> 2. I was thinking of removing the motherboards from the case and
> mounting
> them on a sheet of plywood to be mounted on a wall on my garage.  In
> addition
> to saving space/power it would create an interesting conversation
> piece. 
> What size power supply would/could I use.  Any problems with all
> those
> motherboards running off a single power supply or two?
> 
> 3. If I just run them in their individual cases, how would I
> calculate the
> amount of power used (no monitors of course).  I would hate to see a
> $100
> increase in my electric bill at the end of the month.
> 
> 4. In the vein of saving electricity.  What about booting from a
> single
> machine in order to save power from multiple cd and hard drives?
> 
> I look forward to hearing some ideas.
> 
> Tim Emerick
> 
> 



		
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