Wind/Solar Electrics ???

[SolarFlare]

Modified Semantic Wave is correct.

 

[SolarFlare]

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.

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!

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.

Well, the audio hype that came out then was "2 times
oversampling" followed by 4x, 8x, 16x & 32x
"oversampling". Shister and ignorant marketing people
explained this as "reading the CD 16 times repeatedly
and eliminating the digital errors" "You can eliminate
scratches with this"

In reality the "oversampling" technique was the
development of a digital filter that made the analogue
filter into a simple capacitor to eliminate the
sampling noise.

Any square wave can be filtered enough to produce a
pure sine wave. The trick is the cost. Huge core
inductors and capacitors to handle and smooth out big
quantities of power cost money to design and money to
produce. Not to mention the sheer weight of the beasts.

Multistep waveforms can be filtered much easier. This
is analogous the "oversampling" technique used in CD
players of years past. Digital filtering is much easier
and cheaper than the equivalent analogue filtering.
It's not like an inverter, these days, doesn't have a
computer chip inside then anyway.

How little distortion do you need anyway? Most of it
can be accomplished inside the computer and then just
amplified to useful power levels. At a cost, of course,
and a marketing tool for more money...always.


message

 

[George Ghio]

Tell us why anyone would modify a sine wave.

 

[[email protected]]

Tell us why anyone would modify a sine wave.

It's called "engineering," George.

Nick

 

[Matt Whiting]

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

 

[Keith Williams]

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>

 

[Rich Grise]

"....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

 

[Rich Grise]

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

 

[[email protected]]

[email protected] 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

 

[Steve Spence]

"....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]

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]

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?

 

[Rich Grise]

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

 

[Rich Grise]

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?

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

 

[Steve Spence]

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

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

 

[Steve Spence]

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

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.

 

[Roger]

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.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

 

[Roger]

"....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...

The quality of the wave form is directly proportional to the money you
put into it.

I've used a small generator to power just about everything in here.
I've since upped that to 9,500 watts continuous which seems to work
well. It does tend to mess with the clocks if we're on generator
power for more than a few hours.

I've never had any problems with the computers of printers though.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

 

[Roger]

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.

Purchase a cheap one. They must try. <)

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

 

[SolarFlare]

When a scope is put on the waveform the shape is a
"modified sine wave"

This is not a hard concept.