[Techtalk] OT but I'm desperate.... Windows....!

Meredydd Luff meredydd at everybuddy.com
Sat Oct 19 16:18:20 EST 2002


Uhhmmmm - how does that work?

V = I x R
pd = current x resistance

Considering resistance remains the same, then for current flow to decrease, 
you've got to have pd loss. It's not just a good idea, It's The Law(tm). How 
this occurs is dependent on the power source.

A power source pumps electrons from the positive to the negative pole (of the 
supply, that is). The current is how many it pushes across (one amp is 
defined as a certain number of electrons per second). The pd (or voltage) is 
how "hard" they are pushed - it how much electric potential energy each 
electron has.

A brownout occurs when the power source can't push electrons across fast 
enough to keep up with the current that flows if you put 240V across your 
load circuit. As a result, the pd decreases (V=IR again). Thus, a brown-out 
is indeed a drop in pd, as well as a drop in current.

Meredydd

On Saturday 19 October 2002 15:30, L J Laubenheimer wrote:
> Maria Blackmore wrote:
> > On Thu, 17 Oct 2002, Alvin Goats wrote:
> >> ? wrote:
> >>>It is true that a monitor is usually the most power hungry component of
> >>> a computer, however it is drawing its power from the mains, so doesn't
> >>> affect the computer
> >>
> >>To some extent that is true. However, as I recall from an earlier
> >>message, all of your hardware is running off of one outlet. The power is
> >>shared between outlets, so a power consuming object on one plug is
> >>sapping some power from the other plug.
> >
> > Uhm
> >
> > no.  sorry.  I think not.
>
> I think so.[1]
>
> Power is in Watts(volt-amps)==Voltage(V) x Current(amp), *not* Volts!  You
> are neglecting the variable half of the equation.  Several devices on one
> circuit are said to be "in parallel", therefore the voltage stays constant,
> and the available current is shared between them.
>
> AC Power supplies are rated in terms of Watts.  "Watt refers to a
> time-averaged power flow.  In AC circuits, Power flow varies as a sine
> function.  The "root-mean-square" rate of flow is approximately 65% of the
> maximum flow."[2]
>
> >>This can still lead to a brown out type condition (before tripping
> >>circuit breakers/blowing fueses).
> >
> > If the voltage drop caused by additional load on the same circuit is
> > sufficient to cause problems, then I would suggest that the house wiring
> > needs to be looked at in some depth.
>
> The problem isn't voltage, it's current.  The voltage is regulated by the
> utility.
>
> If you have a 15 amp circuit powering 2 outlets, and those outlets are
> trying to suck 20 amps of draw combined, something loses, and a brownout
> condition can occur before circuit breakers trip.  Computers, for some
> reason, are sensitive to brownout conditions, in spite of their converting
> (AC to DC) power supplies.  That is why line conditioners are used in most
> datacenters.
>
> > Mains voltage is very well regulated, and has a lot of oompf behind it to
> > back it up.  The voltage drop across properly installed cables when
> > addition load is applied should be pretty much negligible, and the
> > voltage droop caused by the additional load should be easily corrected by
> > regulating transformers after a short delay.
>
> But that doesn't say anything about current, which is what is restricted in
> household circuits.
>
> > The time period that the mains voltage droops for doesn't matter anyway,
> > since if the power supply is correctly regulating its output rails then
> > it should have no effect, in fact a well designed power supply should be
> > able to cope with no power coming into it at all for at least half a
> > cycle of 50 Hz or 60 Hz, usually much more (the hold over time).  Power
> > supplies should be able to cope over a range of voltages at least as far
> > apart as 100 and 120 V or 220 and 240V.  I believe (though I'm probably
> > wrong) that the acceptable range of voltages to find on a mains outlet in
> > the USA is 90-130V, and in the UK/europe 210-250.  There is a percentage
> > range defined, though I can't remember it off hand.
>
> If your power supply isn't getting the amperage it needs to convert, it
> starts flaking out.  Talking about voltage alone tells nothing.[1]
>
> > As to the original problem, if it crashes every time you go to print, I
> > would be rather suspicious.  Though the error pasted in another email
> > would seem to suggest that windows is experiencing its equivalent of a
> > kernel panic.
>
> I would suspect: bad/unstable power supply (possibly due to current
> availability problems.), dying cpu, flaky printer port/printer riser.
>
> 				Linda
>
> [1] Strongly recommended reading (these are nice tutorials!):
> http://www.electronics2000.com/basics/basics.html - a basic tutorial on
> electricity and http://www.electronics2000.com/basics/basics2.html, which
> covers basic circuits.  More advanced tutorials can be found off of
> http://www.electronics2000.com/page2.html, but get the basics down first.
> [2] http://newton.dep.anl.gov/askasci/phy00/phy00205.htm

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