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#91
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Wind/Solar Electrics ???
No, it's not, it's a modified square wave
SolarFlare wrote: When a scope is put on the waveform the shape is a "modified sine wave" This is not a hard concept. "Steve Spence" wrote in message ... 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. -- Steve Spence Dir., Green Trust, http://www.green-trust.org Contributing Editor, http://www.off-grid.net http://www.rebelwolf.com/essn.html |
#92
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Wind/Solar Electrics ???
On Wed, 21 Dec 2005 15:48:32 GMT, Rich Grise
wrote: On Tue, 20 Dec 2005 23:00:43 -0800, philkryder wrote: "....It depends how you count "steps"." Indeed. I suppose something like "the number of distinct voltage changes per cycle" might be a good first approximation of something to call steps and to count. In your example I would count something like "3" or maybe "2" or "4" - I always have trouble with boundary conditions... 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? (100/10)+1 = 11 I used to farm. Or this one: Imagine a short staircase, say to a "sunken living room" or some such, of 3 steps: ------------ | ----- | ----- | --------------------------- There are only two steps. on the stairway. The others are landings Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
#93
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Wind/Solar Electrics ???
On Thu, 22 Dec 2005 03:10:59 GMT, Matt Whiting
wrote: Roger wrote: On Wed, 21 Dec 2005 14:29:00 GMT, Matt Whiting wrote: George Ghio wrote: Tell us why anyone would modify a sine wave. To vary the power delivered to a load. Chopping off part of a sine wave cycle is a standard means of power control. 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:-)) which is probably why Saturable core reactors are so popular in industry. Now there is a controller that is a tad on the weighty side. The application I'm familiar with (well I was 10 years ago) was electrically fired glass melting units. The resistive load didn't much care about cross phase interference. :-) The ones I'm referring to were large ovens with, I'd presume, resistive elements as well. I finally gave up and purchased a comercial unit. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com Matt |
#94
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Wind/Solar Electrics ???
SolarFlare wrote:
When a scope is put on the waveform the shape is a "modified sine wave" This is not a hard concept. Actually it's not a modified sine wave, it's still a square wave with many fine steps. Again, it's a marketing term, not a technical one. You don't "modify" the sine wave, you modify the square wave to approximate a sine wave. -- Steve Spence Dir., Green Trust, http://www.green-trust.org Contributing Editor, http://www.off-grid.net http://www.rebelwolf.com/essn.html |
#95
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Wind/Solar Electrics ???
On Thu, 22 Dec 2005 10:22:48 -0500, Steve Spence wrote:
SolarFlare wrote: When a scope is put on the waveform the shape is a "modified sine wave" This is not a hard concept. Actually it's not a modified sine wave, it's still a square wave with many fine steps. Again, it's a marketing term, not a technical one. You don't "modify" the sine wave, you modify the square wave to approximate a sine wave. I like that one, but "approximated sine wave" just doesn't have the same marketing ring to it. :-) Cheers! Rich |
#96
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Wind/Solar Electrics ???
Why don't you ask this in the wind/solar electric NG you dumbass MoFo.
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#97
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Wind/Solar Electrics ???
In article ,
Rich Grise wrote: will work. The HONDA EM50is claims to be a sine wave unit. 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 Except that if you actually had any understanding of the product you were expounding upon, you would know that the generator portion of this product, produces DC Current, that is then supplied to an internal inverter, which then converts the DC current into AC current. The only question being debated about the product is, if produces a true Sinewave output, or a modified Squarewave output, during the conversion process. Apparently you seem to lack visulization capabilities altogether..... Me |
#98
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Wind/Solar Electrics ???
"Roger" wrote in message ... On Wed, 21 Dec 2005 14:29:00 GMT, Matt Whiting wrote: George Ghio wrote: Tell us why anyone would modify a sine wave. To vary the power delivered to a load. Chopping off part of a sine wave cycle is a standard means of power control. 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:-)) which is probably why Saturable core reactors are so popular in industry. Now there is a controller that is a tad on the weighty side. Also, some old systems used self-saturating reactors (magnetic amplifiers, 'magamps') for instrumentation. Things could take some severe environments, but calibration tended to drift a lot. Required fairly frequent 'trip & cals' to keep them in spec. daestrom |
#99
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Wind/Solar Electrics ???
"Keith Williams" wrote in message T... In article , lid says... snip Except for one thing...when they played the CD back unfiltered, people would find their tweeters melting for some weird reason....44.1kHz! at huge powers! 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. Aliasing happens on the analog to digital conversion, not the digital to analog conversion. That's why low-pass filters are put 'in front' of analog to digital converters. When going from digital to analog, all you *really* need is a sample/hold circuit to maintain output until the next digital sample comes through for conversion. But the step change from one sample to the next, if done with a very fast slew rate can introduce some harmonics (rapid step changes are always rich in high harmonics). But this is *not* aliasing ala Nyquist. These can be 'smoothed' with a variety of filter circuits. daestrom |
#100
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Wind/Solar Electrics ???
"daestrom" wrote in message
... Aliasing happens on the analog to digital conversion, not the digital to analog conversion. That's why low-pass filters are put 'in front' of analog to digital converters. You might not call it 'aliasing' -- it's arguably more appropriate to call it 'imaging' -- but a DAC that only outputs unit impulses scaled by the desired output level creates infinitely many replicas of a band-limited sampled input signal. Adding a first order (sample-and-) hold thereby gets you infinitely many replicas scaled by a sinc function and -- as you mention -- typically needs to be corrected or 'smoothed.' It isn't uncommon to purposely make use of one the replicas, though, just as it isn't uncommon to sub-sample a band-limited signal at well below its center frequency. But this is *not* aliasing ala Nyquist. It's all just linear system convolution with sample functions, hold functions, etc. 'Nyquist aliasing' is one of those kinda vauge terms where it's usually clear from the context what's meant, but it doesn't have any particularly formal meaning. (I can't tell you how many times I've seen people stating something like, 'The Nyquist theorem requires sampling at at least twice the highest frequency present in the signal," when of course it says no such thing.) ---Joel Kolstad |
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