AC sine wave: What does increasing the frequency do?

On Sun, 28 Nov 2004 17:54:39 -0600, Commander Dave wrote:

"John Popelish" <jpopelish@rica.net> wrote:
I love this newsgroup because a simple, one sentence question can
generate days of technical exchange that teaches quite a few of us
things we knew but didn't realize. :) --
John Popelish

It amazes me that my simple question on power spawned this much
discussion! I followed a little of it, but for the most part it made me
realize how much I have to learn... :)
Click to expand...
Oh, this is nothing compared to the thread I instigated a couple of years
ago about running a 120V bulb off 240V mains by just putting a diode in
series!

Cheers!
Rich
 
On Sat, 27 Nov 2004 19:39:23 -0800, John Larkin wrote:

On Sat, 27 Nov 2004 20:13:48 -0500, John Popelish <jpopelish@rica.net
wrote:

John Larkin wrote:

We're not getting anywhere on this, are we. Do you propose that a triac
dimmer, driving a resistive load, runing at 50% conduction angle, has
no current-versus-line-voltage phase shift? Even though all the load
current flows in the last half of each cycle? That seems like a phase
shift to me.

Actually, it represents even harmonics, not phase shift

So, if one did a Fourier analysis of this current waveform, the
fundamental current would be in phase with the voltage?
Click to expand...
I don't even know what a Fourier analysis _is_ other than a way of
translating a data set from the time domain to the frequency domain
(transforming?), but my "gut-feeling" is that the zero-crossings would be
identical _of the actual source waves_ - the fundamental would be out of
phase, in the plot of the Fourier-transformed resolved fundamental, but
the zero-crossing would be brought back into sync by the harmonics after
you added them back together.

It's like a sine wave with the half-cycles tilted to one side.

But wouldn't that act more inductive?

Thanks,
Rich
 
On Thu, 02 Dec 2004 09:05:10 GMT, Rich Grise <rich@example.net> wrote:

On Sat, 27 Nov 2004 19:39:23 -0800, John Larkin wrote:

On Sat, 27 Nov 2004 20:13:48 -0500, John Popelish <jpopelish@rica.net
wrote:

John Larkin wrote:

We're not getting anywhere on this, are we. Do you propose that a triac
dimmer, driving a resistive load, runing at 50% conduction angle, has
no current-versus-line-voltage phase shift? Even though all the load
current flows in the last half of each cycle? That seems like a phase
shift to me.

Actually, it represents even harmonics, not phase shift

So, if one did a Fourier analysis of this current waveform, the
fundamental current would be in phase with the voltage?


I don't even know what a Fourier analysis _is_ other than a way of
translating a data set from the time domain to the frequency domain
(transforming?), but my "gut-feeling" is that the zero-crossings would be
identical _of the actual source waves_ - the fundamental would be out of
phase, in the plot of the Fourier-transformed resolved fundamental, but
the zero-crossing would be brought back into sync by the harmonics after
you added them back together.

It's like a sine wave with the half-cycles tilted to one side.

But wouldn't that act more inductive?

Thanks,
Rich
Click to expand...

At the intuitive level, a Fourier series answers the question "how
much does this waveform look like a 60 Hz sine wave? How much like a
120 Hz sine wave?...". The answers are of the form "2 volts, 45
degrees" and such, one answer for DC and one for each harmonic. The
Fourier transform is a math operation that gives these answers. It
produces the same results you could get using a bandpass filter bank
at f, 2f, etc (plus the DC term, the zero frequency Fourier term,
which you'd get using a lowpass filter).

You can do an eyeball Fourier by printing the waveform on a piece of
paper. Suppose some waveform has a basic frequency of 60 Hz. Now plot
a 60 Hz sinewave on another piece of paper and hold it next to the
original waveform. Slide it horizontally until you see the best match,
so that the input waveform "helps" the sinewave template, pushing it
up and pulling it down in the best places. Now make a rough estimate
of how much it helps (amplitude), and how far you shifted the papers
to get the best match (phase.) Repeat for higher harmonics, one at a
time. Fourier!!

The SCR phase control waveform at 50% on has power on the load in the
last half of each half-cycle. That shifts the center-of-gravity of the
waveform later in time from the line voltage wave, so the fundamental
component, the 60 Hz Fourier line, lags. By something like 32 degrees,
some people have calculated in other posts. That does look inductive.

John
 
On Thu, 02 Dec 2004 08:54:22 GMT, Rich Grise <rich@example.net> wrote:

On Sun, 28 Nov 2004 17:54:39 -0600, Commander Dave wrote:

"John Popelish" <jpopelish@rica.net> wrote:
I love this newsgroup because a simple, one sentence question can
generate days of technical exchange that teaches quite a few of us
things we knew but didn't realize. :) --
John Popelish

It amazes me that my simple question on power spawned this much
discussion! I followed a little of it, but for the most part it made me
realize how much I have to learn... :)


Oh, this is nothing compared to the thread I instigated a couple of years
ago about running a 120V bulb off 240V mains by just putting a diode in
series!

Cheers!
Rich
Click to expand...
Bright. Won't last long.

John
 
"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:sdhuq0hafh8bojb8tb8m4a9gailopqid86@4ax.com...
On Thu, 02 Dec 2004 08:54:22 GMT, Rich Grise <rich@example.net> wrote:

On Sun, 28 Nov 2004 17:54:39 -0600, Commander Dave wrote:

"John Popelish" <jpopelish@rica.net> wrote:
I love this newsgroup because a simple, one sentence question can
generate days of technical exchange that teaches quite a few of us
things we knew but didn't realize. :) --
John Popelish

It amazes me that my simple question on power spawned this much
discussion! I followed a little of it, but for the most part it made me
realize how much I have to learn... :)


Oh, this is nothing compared to the thread I instigated a couple of years
ago about running a 120V bulb off 240V mains by just putting a diode in
series!

Cheers!
Rich


Bright. Won't last long.

John
Click to expand...
lasts like forever if the diode is selected correctly
(say 1N4007 or so for standard domestic bulbs)
 
On Thu, 02 Dec 2004 22:02:33 GMT, "peterken" <peter273@hotmail.com>
wrote:


lasts like forever if the diode is selected correctly
(say 1N4007 or so for standard domestic bulbs)
Click to expand...
---
Really? Why would that be?

--
John Fields
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:uj4vq0tcpmgolliicpi8irrad72581mbng@4ax.com...
On Thu, 02 Dec 2004 22:02:33 GMT, "peterken" <peter273@hotmail.com
wrote:


lasts like forever if the diode is selected correctly
(say 1N4007 or so for standard domestic bulbs)

---
Really? Why would that be?

--
John Fields
Click to expand...
"standard domestic bulbs" is any type from say 5W upto 250W
for these types power rating of 1N4007 diode is ok
 
On Fri, 03 Dec 2004 00:34:45 GMT, "peterken" <peter273@hotmail.com>
wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:uj4vq0tcpmgolliicpi8irrad72581mbng@4ax.com...
On Thu, 02 Dec 2004 22:02:33 GMT, "peterken" <peter273@hotmail.com
wrote:


lasts like forever if the diode is selected correctly
(say 1N4007 or so for standard domestic bulbs)

---
Really? Why would that be?

--
John Fields

"standard domestic bulbs" is any type from say 5W upto 250W
for these types power rating of 1N4007 diode is ok
Click to expand...
---
Perhaps you missed this:

"Oh, this is nothing compared to the thread I instigated a couple of
years ago about running a 120V bulb off 240V mains by just putting a
diode in series!"

Notice that it's not a 120V lamp running on 1/2 wave rectified 120V
mains, it's a 120V lamp running on 1/2 wave rectified 240V mains.

That being the case, how much power would a 120V 100W lamp dissipate
if it were being run on 1/2 wave rectified 240V?

Don't forget to consider the tempco and thermal time constant of the
filament... :)


--
John Fields
 
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