[geeks] New lamps for ... er, large UPS for smaller

[Charles Shannon Hendrix]

Tue, 21 Jun 2005 @ 22:29 -0700, Gregory Leblanc said:

> On Tue, 2005-06-21 at 20:19 -0400, Charles Shannon Hendrix wrote:
> > Tue, 21 Jun 2005 @ 13:28 -0400, Nick B. said:
> > 
> > > On Mon, Jun 20, 2005 at 10:08:05AM -0400, Phil Stracchino wrote:
> > 
> > > > Hmmm.......   You have a point.
> > > > 
> > > > Anyone happen to know what the maximum charging current draw of an
> > > > SU3000 is?
> > >
> > > Charging is much less than 30A.  Computer type hardware is also
> > > limited to 80% of a circut, so it can be no more than 24A.  Based on
> > > my 2200s and 1400s I'd guess it would charge at no more than 10A, if
> > > that.
> > 
> > What do you mean by 80% of a circuit?
> 
> Lovely details that one gets into when dealing with AC and non-linear
> components (anything except resistors, essentially).  I'm not quite sure
> where the 80% comes from, but it's what's called "power factor".  Large
[snip]

Ah, you are talking about reactive power in inductive devices.  

The actual ratio varies depending on the circuits involved.  I'm not
sure where you got 80% unless it is someone's rule-of-thumb.

The power factor is a ratio of power used for work to power supplied.
It's only a subset of the overall efficiency of a circuit.

Inductive loads are things like motors, transformers, and solenoids:
they need a magnetic field to operate.  The power used to generate the
field doesn't do any work, but you still have to supply it (and pay for
it).

Induction stores power, and causes a time difference between voltage and
current (think about two sin waves out of sync).  The inductive load
returns to the supply without doing any work.

Since inductors cause current to lag voltage, local capacitors can
correct the problem because they cause current to lead voltage.

I don't understand this will help with much past the UPS transformer
though.

Tons of computer power waste occurs through heat, and I would think it
outweights that lost as reactive power loads.


-- 
shannon "AT" widomaker.com -- ["People should have access to the data which
you have about them.  There should be a process for them to challenge any
inaccuracies." -- Arthur Miller]