Wind/Solar Electrics ???

George Ghio wrote:

Tell us why anyone would modify a sine wave.

It's called "engineering," George.

Nick

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.


Matt

In article ,
lid says...
We previously went through this crap with CD players.
The sampling frequency was chosen to be 44.1 kHz, well
beyond the range of human hearing. No filtering would
be needed.

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,
2kHz is left for the filter, thus a sampling rate of 44.1kHz.
T'was a trade-off of device complexity and data storage (running
time).

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.

Out came the drawing board and complex analogue (and
expensive) filters were designed until one day some
smart engineer discovered they could double the freq.
in a computer and put out 88.2 kHz sampling noise and
use a less efficient and less expensive filter.

Less expensive filter because there is more headroom.

snip

--
Keith

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?

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? ;-)

In any case, it seems that the device you had was effective.
And the only thing I could imagine as having fewer steps would be a
similar device that didn't have the pause at zero...

And yet it was effective -
I wonder if it would have worked with the light dimmer mentioned
above...

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

On Tue, 20 Dec 2005 23:35:15 -0800, meow2222 wrote:

Steve Spence wrote:
philkryder wrote:
Steve - How many equal "steps" are necessary for the MSW inverter to be
a sufficiently close approximation to a "rotary" sine wave?


That depends on what you are driving. A laser printer requires closer
representation than a computer. The manufacturer of a particular load
could tell you that information. The old test of whether something was
sine or some version of square was a lamp dimmer. On a square wave unit
the light goes full bright. We have a touch lamp that will not change
state on MSW, but will on generator.

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

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

Or should we alert the Darwin committee? ;-)

Thanks!
Rich

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

philkryder wrote:
"....We have a touch lamp that will not change
state on MSW, but will on generator"

Do you know if these new smaller Inverter style generators are a close
enough approximation for things like the laser printer?

Just how good are the "sine" like waves on them?

I thought someone was going to put a 'scope on one...


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.

--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

wrote:
Steve Spence wrote:

philkryder wrote:

Steve - How many equal "steps" are necessary for the MSW inverter to be
a sufficiently close approximation to a "rotary" sine wave?


That depends on what you are driving. A laser printer requires closer
representation than a computer. The manufacturer of a particular load
could tell you that information. The old test of whether something was
sine or some version of square was a lamp dimmer. On a square wave unit
the light goes full bright. We have a touch lamp that will not change
state on MSW, but will on generator.


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


My fridge and well pump are not among these devices.


--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

wrote:
George Ghio wrote:


Tell us why anyone would modify a sine wave.


It's called "engineering," George.

Nick


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?

--
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 14:06:05 -0500, Steve Spence wrote:

philkryder wrote:
"....We have a touch lamp that will not change
state on MSW, but will on generator"

Do you know if these new smaller Inverter style generators are a close
enough approximation for things like the laser printer?

Just how good are the "sine" like waves on them?

I thought someone was going to put a 'scope on one...


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.

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