Has anyone seen circuitry for moving a 'modified sine-wave" output more towards a real sine wave shape? A few of my charges don't like being fed the modified stuff and I think my Blackberry charges was ruined by it.
The AA NiMh charger doesn't seem to like it much either.
I'd be happy with a one amp output.
mike
The "modified sine" from most inverters does cause increased wear on devices, especially motors and switching power supplies. They shouldn't be used except for the occasional power outage or camping trip.
Filtering a modified sine wave doesn't work well. A simple inductor-capacitor filter is bulky and puts a lot of strain on the inverter. More complex designs for 120VAC or 240VAC will be enormous. A 150W sine wave inverter doesn't cost much so save yourself the trouble. I'd avoid the Wagan brand.
-- I will not see posts or email from Google because I must filter them as spam
Take a look at Don Lancaster's "magic sine waves". He concocts long strings of ones and zeros to create a pulse-width-modulated drive that has very little harmonic content out to beyound the tenth harmonic. The filters for the higher harmonics can be a lot less bulky than those you need for the 5th and 7th harmonics present in a "modified since wave".
The virtue of the modified sine wave is that it doesn't have any even harmonic content. You can take a leaf out of Don Lancaster's book and make "magic modified sine waves" with a lower odd harmonic content. The first step on the road might look something like this - - ---- - -
--- - - - - --- - - - - --- - - ----- - - I thought about this once, years ago, but didn't get far enough to work out any optimal bit sequences - I was looking at higher frequency sine waves (more than two orders of magnitude faster than 50/60Hz) and the clock frequencies got impractically high before I could come up with anything interesting.
-- Bill Sloman, Nijmegen
use a 1:1 or isolation power transformer.. I've suggested that to a good many that has solved those issues..
You may want to shop around for used transformer, they are not cheap but they do solve the issue..
Or just get a small one for one unit..
Not very practical and after filtering. You most likely won't end up with 120 VAC RMS anymore after all the harmonics are gone unless you step it up with an autoformer or something.
I'd just buy an inexpensive true sinewave inverter off the internet. around 250 Watts used to be pretty common.
boB
I think you might have misidentified the goal. If the goal is to make switched mode chargers happy, this can be done with a simple series resistance. What that does is reduce the peak current draw. Turning MSW into sine is possible but not worthwhile, ie it takes too much work/equipment.
NT
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