Wind/Solar Electrics ???

Take it to mean that you can't prove that true sine wave inverters don't exist.

Modified Square Wave inverters = True

Modified Sine Wave inverters = False

Careful. Even true 'rotary' generators don't always put out a true sine wave.

Even the very, very large commercial generators used in power plants, don't put out a 'pure' sine wave. The number of stator slots and rotor geometry cause a small amount of harmonics. The exact connections of windings is often used to help improve the fundamental and minimize some of the higher harmonics (6th, 9th and 11th are some of the more troubling ones).

After it passes through several transformers, getting to the substation, most of the harmonics have been filtered out by the characteristics of the transformers.

So the question, as usual, boils down to 'how good, is good enough?'

daestrom

A lot of ac loads are quite happy on dc. Almost anything that rectifies the mains waveform will run fine on dc of V_mains x 1.414.

NT

What are those Phil?

NT

It's called "engineering," George.

Nick

Your story is ready for Snopes (sounds good, but less than the truth). To get to a 20kHz bandwidth the signal must be sampled at greater than 40kHz (see Nyquist). If *everything* above the nyquist limit isn't filtered these artifacts will be aliased. Given that most engineer's junkbox doesn't contain perfect filters,

BS. Were it unfiltered aliasing would make the CD sound terrible. The filter has to be in there for any sampled system. They didn't "all of a sudden" figure out that they needed a filter.

Less expensive filter because there is more headroom.

snipped-for-privacy@care2.com wrote....

"A lot of ac loads are quite happy on dc. Almost anything that rectifies the mains waveform will run fine on dc of V_mains x 1.414. "

...unless there is a transformer at the input to the power supply. Only thing that'll happen then is the transformer might get hot.

Randy

Heh. Programmers run into this all of the time - it's called "the fencepost effect". If you have a 100' fence, and there's a post every 10', how many posts do you need?

Or this one: Imagine a short staircase, say to a "sunken living room" or some such, of 3 steps:

------------ | ----- | ----- | ---------------------------

Now, if you had three apples, you'd be able to count them, 1, 2, 3, and point at the middle one.

OK, now go up those three steps, counting along, and point at the middle one. Then go down, counting again, and _now_ point at the middle one.

Isn't that cute? ;-)

I think very probably not very well, if at all, based on what others have said.

But, if you're on an inverter already, I think there'd be a more efficient kind of light dimmer that you could find, maybe that runs off the battery voltage. Or sync up your triac or SCR dimmer to the inverter itself - hmmmm.... (this one had a sync in/out so that they could be paralleled.)

Thanks! Rich

Well, don't plug a 120VAC wall wart into 170VDC!

Or should we alert the Darwin committee? ;-)

Thanks! Rich

I don't have one (inverter/generator) to test. If it's a SW then yes, it will work. The HONDA EM50is claims to be a sine wave unit.

My fridge and well pump are not among these devices.

Really... Wouldn't they rather modify a square wave to approximate a sine wave? What would be the point of modifying a sine wave, when a sine wave (or close approximation) is the required result?

To vary the power delivered to a load. Chopping off part of a sine wave cycle is a standard means of power control.

Matt

It seems pretty obvious that a mechanical generator should put out a relatively pure sine wave - it's just this big rotating magnetic field and a couple of coils, after all. :-)

As a matter of fact, it's a little hard for me to visualize how someone would make anything _other than_ a plain vanilla sine wave using just a rotating magnet and a coil.

Thanks! Rich

I hope you're not serious here.

They don't make a sine wave and modify it, they make a rectangular wave and call it a "modified sine wave" because it passes enough tests for harmonics and crap that it will run most stuff, and they can get away with it. ;-)

Anybody wanna do an FFT of various duty-cycle waveforms, and give us real THD information, and how that relates to power factor, and etc, and etc, and etc?

The one inverter I've ever had my hands on the guts of made a waveform like this:

---- ---- ---- | | | | | | - - - - - - | | | | | etc.

- ---- ----

And the regulator was just based on an ordinary rectifier - they didn't care about RMS, or it was scaled to get "close enough".

But I do wonder, what does the harmonic content really do when you vary the duty cycle?

Some years ago, in the USAF, I saw some pulses on a spectrum analyzer, and they had some really pretty envelopes. :-)

Thanks, Rich

Inverter units do not provide mechanically driven electrical output to the load, they run it through an inverter for frequency and voltage control.

That's my point. There are modified square wave inverters (marketed as Modified Sine Wave), and there are "Sine Wave" inverters, which are really MSW's with such fine steps that finicky equipment can't tell the difference. There are a few folks on this group trying to justify the "Modified Sine Wave" sales moniker but there is no logic to it. Folks who should know better, but can't find it easy to "agree" with george even for a moment. It even kills me to do it, but hey, he has a point for once.

That makes three phase SCR (Silicon controlled rectifiers and not saturable core reactors) interesting as chopping off part of the wave form develops spikes and harmonics that tend to make the control of one phase interact with the others.

I've built a lot of them for single phase control, but I never once was able to build one for three phase that didn't interact. Turn one up and maybe another would go up, Turn the second down and the other two might go up or down. Twas interesting