Control the amplitude of a 115VAC

Any idea or suggestion on how to play
with the amplitude of a 115VAC?

Note: amplitude, not PWM...

Regards,
Start a New Thread

Basically just one way of doing it:
-rectify it so you get DC
-use the PIC and its PWM to modulate the DC into a sinewave
-also use the PIC to switch the H-bridge to change output polarity for every second half wave.

This is what is done in commercial DC to AC sinewave inverters, and I've even seen a PIC as
the control chip in one of those...

globalpositioning wrote:

> Any idea or suggestion on how to play
> with the amplitude of a 115VAC?
>
> Note: amplitude, not PWM...
>
> Regards,

--
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LAST UPDATED: 23/08/2003
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Regards
Eirik Karlsen Start a New Thread

--- In p..., "globalpositioning"
wrote:
>
> Any idea or suggestion on how to play
> with the amplitude of a 115VAC?

Lamp dimmers do that, and there are some that can be controlled digitally.

What range of output voltages do you need, and how much current will
the load require?

Would a few different amplitudes be satisfactory, or do you need
smooth variability?

Must the output waveform be sinusoidal?

Best regards,
John

Start a New Thread

--- In p..., "jmsmith871" wrote:
>
> --- In p..., "globalpositioning"
> wrote:
> >
> > Any idea or suggestion on how to play
> > with the amplitude of a 115VAC?
>
> Lamp dimmers do that, and there are some that can be controlled
digitally.
>
> What range of output voltages do you need, and how much current will
> the load require?
>
> Would a few different amplitudes be satisfactory, or do you need
> smooth variability?
>
> Must the output waveform be sinusoidal?
>
> Best regards,
> John
>

Actually, lamp dimmers don't change the amplitude. They are phase
angle fired circuits that do a type of PWM by turning on a triac at
some phase angle other than 0 degrees. The triac conducts until the
following zero crossing. What you get is a sine wave with the front
edge squared off. If the device is set to near 100% you will get a
pretty nice sine wave. But the leading edge moves to the right for
increasing firing angles.

If you really want to adjust the amplitude of 115VAC and maintain a
sine wave (not PWM) then a variac (variable transformer) is about the
only way. Control the variac with a stepper motor or, better, a servo
motor (not an R/C servo).

Square wave inverters can get arbitrarily close to a sine wave by
combining harmonics at various amplitudes. They're not perfect but
nothing downstream complains.

So, we need to know more about WHY you want to control the amplitude
before we can suggest HOW.

Richard

Start a New Thread

John,

Thanks. Yes, I know about dimming but, I do not want to use
the typical dimmers that PWM chopping the wave in order to
control the power. Instead, I want to control the amplitude (I read
we can use IGBT).
Obviously and you are right, I need to that via digital.

115VAC @1A is just enough right now but I think I would
need up to 277VAC and some 7 amps.

It is ok a few settings for amplitude, while variability would be
the best.

Quasi-sinusoidal is enough...

Ideas?

Thanks,

----- Original Message ----
From: jmsmith871
To: p...
Sent: Wednesday, September 17, 2008 6:44:30 PM
Subject: [piclist] Re: Control the amplitude of a 115VAC
--- In piclist@yahoogroups .com, "globalpositioning"
wrote:
>
> Any idea or suggestion on how to play
> with the amplitude of a 115VAC?

Lamp dimmers do that, and there are some that can be controlled digitally.

What range of output voltages do you need, and how much current will
the load require?

Would a few different amplitudes be satisfactory, or do you need
smooth variability?

Must the output waveform be sinusoidal?

Best regards,
John Start a New Thread

Thanks,

----- Original Message ----
From: Eirik Karlsen
To: p...
Sent: Wednesday, September 17, 2008 6:02:08 PM
Subject: Re: [piclist] Control the amplitude of a 115VAC
Basically just one way of doing it:
-rectify it so you get DC
-use the PIC and its PWM to modulate the DC into a sinewave
-also use the PIC to switch the H-bridge to change output polarity
for every second half wave.
This is what is done in commercial DC to AC sinewave inverters, and
I've even seen a PIC as
the control chip in one of those...

globalpositioning wrote:
Any idea or suggestion on how to play
with the amplitude of a 115VAC?
Note: amplitude, not PWM...
Regards,

--
************ ********* ********* ********* ****
VISIT MY HOME PAGE:

LAST UPDATED: 23/08/2003
************ ********* ********* ********* ****
Regards
Eirik Karlsen Start a New Thread

Dear, ... (what is your name?)

My experience with electronic control of high power is practically
nil. Richard mentioned the possibility of using a Variac, and
controlling it with a servo. That should work. I sometimes use a
Variac, manually controlled, in various experiments around the shop.

You didn't mention how quickly the amplitude would need to change in
response to a digital control signal. A servo-controlled Variac might
take up to a second, or so, to change the amplitude. Less for small
changes.

That exhausts my knowledge on this subject. Good luck in your quest.

Best regards,
John
--- In p..., Global Positioning
wrote:
> John,
>
> Thanks. Yes, I know about dimming but, I do not want to use
> the typical dimmers that PWM chopping the wave in order to
> control the power. Instead, I want to control the amplitude
> ...
>
> 115VAC @1A is just enough right now but I think I would
> need up to 277VAC and some 7 amps.
>
> It is ok a few settings for amplitude, while variability would be
> the best.
>
> Quasi-sinusoidal is enough...
>
> Ideas?
>
> Thanks,

Start a New Thread

Mr. NoName,
Google is very helpful, use it a little more...

Here is a PIC16 based inverter, with schematics and source code:
http://www.4shared.com/dir/2136086/3afe23e/sharing.html

High power analog electronics can be some of the most difficult
stuff to handle in the electronics area... simple in theory but not quite
so simple in practice.

The fact that you even asked your question reveals that you're moving
into an area that you're not yet ready for.

To get to grips with some of the theory of power electronics see this excellent
page with tons of info:
http://ece-www.colorado.edu/~pwrelect/book/slides/slidedir.html

Global Positioning wrote:

>
> John,
>
> Thanks. Yes, I know about dimming but, I do not want to use
> the typical dimmers that PWM chopping the wave in order to
> control the power. Instead, I want to control the amplitude (I read
> we can use IGBT).
> Obviously and you are right, I need to that via digital.
>
> 115VAC @1A is just enough right now but I think I would
> need up to 277VAC and some 7 amps.
>
> It is ok a few settings for amplitude, while variability would be
> the best.
>
> Quasi-sinusoidal is enough...
>
> Ideas?
>
> Thanks,

--
*******************************************
VISIT MY HOME PAGE:

LAST UPDATED: 23/08/2003
*******************************************
Regards
Eirik Karlsen Start a New Thread

John,

Thanks, good idea. The thing is I want to control some
public lights with your Variac idea in order to save some
KW. But using thyristors and similar is noisy.

Thanks,

Carlos A. Estrada

----- Original Message ----
From: jmsmith871
To: p...
Sent: Friday, September 19, 2008 7:45:36 AM
Subject: [piclist] Re: Control the amplitude of a 115VAC
Dear, ... (what is your name?)

My experience with electronic control of high power is practically
nil. Richard mentioned the possibility of using a Variac, and
controlling it with a servo. That should work. I sometimes use a
Variac, manually controlled, in various experiments around the shop.

You didn't mention how quickly the amplitude would need to change in
response to a digital control signal. A servo-controlled Variac might
take up to a second, or so, to change the amplitude. Less for small
changes.

That exhausts my knowledge on this subject. Good luck in your quest.

Best regards,
John

--- In piclist@yahoogroups .com, Global Positioning
wrote:
> John,
>
> Thanks. Yes, I know about dimming but, I do not want to use
> the typical dimmers that PWM chopping the wave in order to
> control the power. Instead, I want to control the amplitude
> ...
>
> 115VAC @1A is just enough right now but I think I would
> need up to 277VAC and some 7 amps.
>
> It is ok a few settings for amplitude, while variability would be
> the best.
>
> Quasi-sinusoidal is enough...
>
> Ideas?
>
> Thanks, Start a New Thread

If saving energy is the goal, reducing the voltage on incandescent bulbs is
a poor choice. The quality of the light diminishes much more quickly than
the energy used. You'd do better to have MANY full brightness lights of
low wattage, and selectively switch off groups. That way the color would
remain the same, even as brightness decreases. Of course, it's stepwise,
not continuous (unless you have a really big bunch of bulbs). Could be
done, though.

At 04:57 PM 9/19/2008, you wrote:

>John,
>
>Thanks, good idea. The thing is I want to control some
>public lights with your Variac idea in order to save some
>KW. But using thyristors and similar is noisy.
>
>Thanks,
>
>Carlos A. Estrada
>
>----- Original Message ----
>From: jmsmith871
>To: p...
>Sent: Friday, September 19, 2008 7:45:36 AM
>Subject: [piclist] Re: Control the amplitude of a 115VAC
>
>Dear, ... (what is your name?)
>
>My experience with electronic control of high power is practically
>nil. Richard mentioned the possibility of using a Variac, and
>controlling it with a servo. That should work. I sometimes use a
>Variac, manually controlled, in various experiments around the shop.
>
>You didn't mention how quickly the amplitude would need to change in
>response to a digital control signal. A servo-controlled Variac might
>take up to a second, or so, to change the amplitude. Less for small
>changes.
>
>That exhausts my knowledge on this subject. Good luck in your quest.
>
>Best regards,
>John
>
>--- In piclist@yahoogroups .com, Global
>Positioning
> wrote:
> >
> >
> > John,
> >
> > Thanks. Yes, I know about dimming but, I do not want to use
> > the typical dimmers that PWM chopping the wave in order to
> > control the power. Instead, I want to control the amplitude
> > ...
> >
> > 115VAC @1A is just enough right now but I think I would
> > need up to 277VAC and some 7 amps.
> >
> > It is ok a few settings for amplitude, while variability would be
> > the best.
> >
> > Quasi-sinusoidal is enough...
> >
> > Ideas?
> >
> > Thanks,
> Start a New Thread