I don't have the original post so forgive me for commenting here.
If this something like the switch-mode Makita charger I bought with my
last drill, it will actually be much happier with this inverter than
the old transformer-based chargers were. Just like typical computer
power supplies etc. - not only do they not care about sine vs modified
sine, they would be just as happy with 110VDC.
I know the DeWalt's are notorious for going up in smoke though.
Probably unnecessary.
I was wondering about some kind of LC,RC,etc filter myself,just a
couple weeks ago. I wonder if those EMF/RFI filters would do anything?
They're intended to take out high frequency interference, whereas the
distortion components of a modified square wave inverter go way down
to the third harmonic. They will do *something* but probably not what
you'd hoped.
Does anybody have any info on this? I was thinking of something you
could plug into the inverter,and plug "sensitive" stuff into,like a
"filtered" power strip.
I've often thought the same thing, but the only way I could see
pulling it off would involve LC filtering and a step-up transformer,
since any useful amount of filtering would reduce the RMS voltage
delivered.
My only other thought was to modify the output stage of the inverter
to output a sine wave,erm,it could be done if ya know what you're
doing,but probably not very easy.
If you value your time, you'd be better off to purchase!
Maybe like a 200uf cap,and 3H choke as a starting point?
If you want to experiment, use two chokes, with one choke from each
output terminal to one side of the load, and the cap directly across
the load.
I dunno.
One other consideration is loss in the filter,and (ermm,whats it
called...it's late.) basically the amount of power the filter can let
through to the load,has to do with the impedance(s) and Q and whatnot.
Remove components of the input waveform and you reduce the RMS value
of the output, yep.
Any info on something to make the output of "modified sine wave"
inverters more like a real sine wave,and filter those nasty harmonics
would be awesome. ;-)
Although modified sine has significantly reduced harmonic distortion
compared to a square wave, the first significant harmonic is the third
(180Hz assuming 60Hz output) so I suppose the ideal filter would be a
brick wall at around 100Hz.
You can certainly take the edges off with a more realistic filter, but
if you do enough filtering to be reasonably effective, you're going to
run up against the voltage problem.
Now, what I'd REALLY like to know is the nature of a Trace device that
came and went several years ago, called the COSINE. I have it listed
as a "new" item in a supplier catalogue from 1997. "Use it with
modified sine wave inverters and get pure sine output," it says. No
power rating quoted, around US$350 at the time, and about 10lbs.
Intended for critical devices (like your filtered power bar idea) it
did not claim to globally "convert" the output of the inverter.
What could it have been but a whacking LC filter with a voltage boost?
From time to time I've mentioned this gizmo but it's hard to find
anyone who had even heard of the thing. Seems to me one fellow did
perk up once and mentioned power handling in the 600W range, but that
could be an invented memory.
But these days you *can* get a 600W sine inverter for that kind of
money.
-=s
