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Larry

(Floating Mind) wrote in news:4475-44DB3A3B-1511
@storefull-3116.bay.webtv.net:

It's my understanding that a person should never use a modified
sinewave
inverter with a laptop, that we should always use pure sinewave
inverters with laptops, as the modified sinewave units are harmful to
the life of the laptop's battery.

Question #1: Is this true?

No. This is how we sell much more expensive inverters to the mis-
informed.

Today's power supplies, like the one running your desktop PC as you read
this, don't really care what the input looks like. The first thing these
"switching power supplies" do is to rectify whatever input AC you put to
them into DC, which is filtered smooth by a large electrolytic capacitor.
Unless the input is so high it blows the cap or diode, it's fine. You
don't even need a "protector" because the damned "protector" is INSIDE
the power supply! Sales BS also sells "protectors". Whatever DC comes
out of the input rectifiers is fed to switching transistors that convert
the DC into an awful-looking SQUARE WAVE, that waveform your sinewave
salesman warned you about! It even has all kinds of crazy pulses
sticking out of it and is very high in frequency. The square waves vary
in pulse width, caused by the regulator IC that creates the square waves.
It's called "pulse width modulation". Those hybrid cars put these pulses
of DC to their drive motors the same way.

That doesn't matter what that waveform looks like, either, because after
a small toroid transformer drops the 170V square wave down to a 5 and 12V
square wave we're just going to rectify it, again with another group of
diodes and smooth out the pulses, yet again, into smooth DC with another
filter cap before sending it into the computer.

The little custom IC that sends the square waves to the switching
transistors has a circuit that monitors the DC output, the important
output. It then adjusts the drive pulse width on the switching
transistors to create, quite exactly, the DC output voltage,
automatically compensating for a wide variery of AC input voltages and DC
load currents. The output is a rock-steady DC voltage with no pulse
component at all no matter what the input AC is over its design input AC
voltage. It doesn't even matter if you short the output as a little
series sensing resistor, measuring the output current, feeds information
back, again, to that little IC that, "HEY! This idiot wants TOO MUCH
CURRENT!" The IC, then, simply switches off its pulses and the DC output
voltage until you clear the load or short condition and recycle the AC
input voltage...fully protected. If something tries to make the output
go too high, it also switches off the pulses. Switching power supplies
are nearly indestructable within reason.

Your inverter, by the way, is, itself, a switching power supply that
simply doesn't have a rectified output. It's waveform is created from
very high frequency pulses that vary in width over the course of the 60
Hz pseudo-sinewave from near zero to near full width. The pulses are
filtered into the actual output sinewave by a filter that passes 60 hz
and blocks 200 Khz, the pulse frequency.

This same technology is even used in AM broadcast transmitters! The
Harris DX-50 50,000 watt AM blowtorch all the US major transmitters use
is a very neat switcher, too! There are over 200 switching "modules"
that switch at the transmitter's radio frequency, from 550 to 1600 Khz.
Audio input to the transmitter is fed to a digitizer that controls each
little module's on-off switch. With no audio, half the modules are on,
putting out a 50KW carrier to the big antenna. As the audio goes
positive, more modules are turned on. As the audio goes negative, less
modules are turned on, leaving only 1 module putting out 100 watts at
full negative modulation. Voila, AM radio! The advantage is the Harris
uses 55KW from the power company....instead of 200KW the old tube-type AM
transmitter used to drink...MUCH more efficient, like your laptop's power
supply which hardly gets warm at full load.

Question #2: How do I tell the difference? I have 2 inverters I use on
my boat, each from a different manufacturer, and neither one says
anything about the sinewave characteristics.

Lionheart's Dell Latitude has a few thousand hours running off the
cheapest Radio Shack 1KW inverter, remotely mounted in the battery
compartment of the engine room by yours truly remoting its little power
switch (which turns that IC on and off with almost no current, not
turning 100A on and off.) Works just fine, even when someone gets hungry
and winds up the timer on the microwave oven.

I'm using a little 175 watt inverter Radio Shack put on sale for $30 to
run the AC power brick (switcher) of my Gateway notebook in my car. A
500 watt Tripplite inverter runs it in my service truck, the same one
that powers my workbench.

As you can see, you've been lied to, many times. The MOST important
thing you can add to ANY computer that doesn't run off a battery, like
your laptop, is a UPS (Uninterruptable Power Supply). THESE keep WinDOS
from scrambling what's being written to the hard drive when the lights
blink or go out! That's very important. Now, don't go looking at the
output waveform of ANY of these UPS AC supplies the COMPUTER STORE sold
you, the same jokers that said you needed a pure waveform from a $800
inverter. UPS output waveforms look JUST AWFUL!....but, as you can see
above, that matters not, either....(c;

Oh, and if any of you want to remote the power switch of any inverter to
the cabin where it's handy, just take the inverter apart and solder some
really small wires across the existing little power switch and route the
wires to your "control point" in the cabin. I'm using a tiny mini toggle
switch at the nav station by the computer in a little panel that also has
an AC-powered neon indicator next to the switch running off the
inverter's output AC. The neon lamp lets me see, "yes the switch is on
and running the battery down" (so my forgetful captain MAY, if we're
lucky and he notices it, turn it off before he leaves the boat) and "yes,
the inverter is working and putting out some high voltage AC" and "from
the lamps brightness, it looks like it's about the right voltage, close
enough for government work".

There, now you don't have to listen to the inverters obnoxious buzzing
noise that sounds like a housefly or its cooling fan that sounds like a
Boeing 737 taxiing for takeoff...while you're trying to take a NAP
because it's in the ENGINE ROOM, where it belongs!