On Sun, 17 Nov 2002, pensioner wrote:

> For these dual conversion phenomenon dunnah forget to take into account the
> efficiency of the "modified sine wave" converter 12vDC-> 120vac.  Check the
> waveform before deciding that cheaper is better.  The computer powersupply
> may have some limitations regarding waveform.  It expects a pretty clean
> sinewave.  Most inverters do a stepped approximation of a sine wave.  Check
> before you plonk down those IBM dollars.

I doubt most laptop power supplies will care.  They're all switching
supplies these days, which means the first thing that happens to the
incoming AC is it's rectified into DC.  I doubt the rectifier will much
care if the sine wave is stepped or not...heck, a square wave would
probably be all right as long as the diodes weren't running too close to
their rated limits.

My laptop is also very omnivorous when it comes to input power
ratings...the spec is something like "90-240V, 50/60 Hz" which suggests to
me that it's not very sensitive to power quality.

I think where you can get into trouble with odd waveforms is with
transformer-driven equipment, where a waveform that's too far from a sine
wave can drive the core into saturation and generate a *lot* more heat
than normal.

An odd waveform may affect the accuracy of any *measurements* you do
on the AC side.  Most AC voltmeters will only read accurate RMS values for
pure sine waves.

             _ _
  __ _ _   _| | |  | David M. Brodbeck (N8SRE)              Ypsilanti, MI
 / _` | | | | | |  +-----------------------------------------------------
| (_| | |_| | | | @ cyberspace.org
 \__, |\__,_|_|_| "I thought it was another false start in the never-
 |___/             ending, weird hope that within our lifetime, we could
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                   us humans and kill us.  Mankind will have accomplished
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