Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sat, 28 Oct 2006 00:55:10 -0600, sylvan butler
<ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<slrnek5vme.vse.ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxx>:

>On Mon, 23 Oct 2006 23:42:22 -0400, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> No I am not ;-) What you describe is a very low-resolution way ( max 8 dim
>> levels at 1000 hz) to dim AC power using TRIACS or back-to-back SCRs.
>
>Your prediction of 8 dim levels is without basis or merit.

We disagree, and you also disagree with the physics of the matter IMO.

>Assuming 60hz.  Typical phase control the triac must be triggered 120
>times per second at a TBD offset after the zero crossing.

Right. And because you are not synchronized with the power line, you are not
synchronized with the zero crossing and so the TBD (To Be Determined) offset
from the zero crossing is not known and *cannot* Be Determined. be

Whatever periodic waveform you use, the dimming value on the first cycle
depends on _when_ you start that periodic waveform, right?

And since you are not synchronized, by definition, the dimming level on the
first cycle is unknown. Right? And is unknown on the second half cycle, etc.

In other words, your 'approach' does not use the  between dim level and delay
in sec, degrees or radians.

>If the triac
>is instead triggered exactly twice as often, it will function exactly
>the same -- the output A.C. waveform will be identical.  Same if the
>triac is triggered exactly 4x as often.  Or 8x as often.  8x is 960/sec.

Sure. As I wrote previously, what happens to the control voltage _after_ the
threshold is reached in any given half cycle has no effect on operation.

The dim level is determined completely by the "To Be Determined" offset as
you've stipulated. But your system has no way of determining the offset, so it
has no (intended ) way of dimming in a deterministic way except by skipping
entire half-cycles.

>If I instead trigger at 1000/sec, that is a max of 4% error when it
>happens at random instead of synchronized to zero crossings.

??? Where does 4% come from?

0.4% (not 4%) relates to how close 960 is to 1000 but that's not relevant to
calculation of the dimming error.

You've already agreed that dimming is determined by the offset after zero
crossing (units = seconds, radians, or degrees), so the calculation of the
dimming error by definition looks like:

Percent Error = (TO-AO)/TO *100%

where TO = Theoretical Actual Offset after zero crossing ,
		in seconds, radians, or degrees
      AO = Actual Offset after zero crossing,  in seconds,
		radians, or degrees


What values do/would you use in this calculation ?

>This error has imperceptible effect (to my eye when using incandescent
>lighting).

What does your TRIAC-based dimmer output look like on a scope?

A dimmer curve for TRIAC dimmers shows the relationship between dim level and
offset (in seconds, radians or degrees).

 See my spreadsheet at
http://www.econtrol.org/dimmers/TRIACDimmerCalcs_MFHult.pdf

Please describe the relationship you use between your 'waveform' and the
resulting _constant_ , non-flickering  dim level.

... Marc
Marc_Hult
www.ECOntrol.org