Re: X10 signals can be TOO strong!

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 15 Dec 2006 03:18:50 GMT, "Alan Vogel" <avogel2@xxxxxxxxxxxxx> wrote in
message  <uuogh.5921$Gr2.922@xxxxxxxxxxxxxxxxxxxxxxxxxx>:

>The inductor in series with the load is there to limit di/dt.  It was
>probably required by the FCC to reduce EMI.

CE has EMI standards but US seem non-existent. Consumer tolerance for dimmer
and filament hum and buzz may be the controlling factor. Whatever the reason,
the snubber circuit is an LRC  network even if the inductance is entirely owing
to the load and not part of the device as is the case with a built-in choke.

>I think this is all starting to make sense.  The highest di/dt transition is
>when there is a heavy load and the conduction angle for the triac is ~4.16
>ms in from the zero crossing (50% dim).

4.16 ms is indeed 50% into the half-cycle, and so is peak voltage, and,
assuming the filament is as at constant temperature during any given cycle and
thus R ~ constant, is also peak current. But at the peak,  di/dt = 0 , not
"highest".  Or by "di/dt transition" did you mean the second derivative?

(And FWIW, 4.16 ms is about 71% of RMS voltage and 33% of luminous intensity
for typical incandescent lamp and not "50% dim" by those measures of dimming.)

>This high current pulse must have
>coupled back into a high impedance node (either the zero crossing detector,
>or the XTAL input pin on the uP).

Not to dismiss the possibility, but why "must have" ?

>Either way, the altered timing caused
>abnormal conduction angles which showed up as flicker.

>Increasing the value of the inductor attenuates the signal enough to
>alleviate the symptom.

This the fix I mentioned that SmartLabs put in place for INSTEON .

The tendency to flicker with increased load could conceivably  be caused by
decrease in series inductance (and consequent decreased attenuation) with
increased current (load). The inductance of non-gapped inductors like the rods
and toroid used in dimmers does decrease with current, but I don't know the
magnitude of the decrease or whether it is significant with a negligible DC
component.

... Marc
Marc_F_Hult
www.ECOntrol.org