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

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

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

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

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

Why don't you ask this in the wind/solar electric NG you dumbass MoFo.

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

"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

"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

"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