Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, 23 Oct 2006 18:06:07 -0600, sylvan butler
<ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<slrnejqm7f.a3i.ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxx>:

>On Mon, 23 Oct 2006 11:25:18 -0400, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> Or are you talking about lamps or LED's  operated on DC?
>> Is so, there are DMX512->PWM and 0-10vdc analog-> PWM converters that
>> modulate DC.
>
>I'm modulating D.C.,

So you first rectify the AC ?

>or rather, creating modulated D.C.

>The technique
>of modulating the D.C. is PWM.  That D.C. is then used to switch a
>triac to control A.C. loads.

OK. But what you end up with is a poorly-timed control signal for the TRIAC
gate. What's the point? You end up with more noise and less resolution (of
different dim levels) than if you were synchronized. I guess I answered my
own question: you don't have to synchronize with the zero crossing ;-)

>Phase syncronization is mainly needed to
>control R.F. and sometimes to control switching transients.  With fairly
>low power loads (typically under 200 watts) R.F. is minimal and
>controllable in other ways.  Switching transients aren't significant
>with primarily resistive or incandescent loads.

See my other comments.
>
>> There are of course many DMX512--> AC dimmer and 0-10vdc --> AC dimmers
>
>You seem to be confusing how the dimmer is controlled (with DMX or
>0-10vdc or...) with how the dimmer controls the A.C.  I'm doing the
>latter.  Not real interested in the former at the present time.

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.

... Marc
Marc_F_Hult
www.ECOntrol.org