Re: I think they've done it again.

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
> "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
> >"Keep thinking Butch, that's what you're good at!"  :-)
>
> I'm not sure whether that's a reference to "Butch the Bulldog" or someone
> else. ;-)

Butch Cassidy and the Sundance Kid . . . I think it was right after the
famous knife fight scene with Harvey (the 7 foot Lurch, from the Addams
Family).  Butch uses creative thinking to win a potentially hopeless
encounter:

http://www.imdb.com/title/tt0064115/quotes

Butch Cassidy: No, no, not yet. Not until me and Harvey get the rules
straightened out.
Harvey Logan: Rules? In a knife fight? No rules.
[Butch immediately kicks Harvey in the groin]
Butch Cassidy: Well, if there aint' going to be any rules, let's get the
fight started. Someone count. 1,2,3 go.
Sundance Kid: [quickly] 1,2,3, go.
[Butch knocks Harvey out]

(If you've seen it, you'll never forget it!)

> A consensus seems to be forming among those seeing the
> flickering that it only occurs when a switch has more than
> ~250W (total) connected and is dimmed to 50% or less.

So, this is a state where the triac is passing a relatively high amount of
current per cycle.  Why would dimming below 50% be important?  Is that when
the triac is likely to put "spikes" out on the line?   If electrical
circuitry can be compared to water flow in pipes then quickly interrupting
the flow of water, as in a shower massage, causes stress on all nearby
joints and fittings.  Is the analogy even slightly on target as to how triac
noise can affect other components ????  :-)

> This puts the triac switching point near the peak of the line
> voltage and at the furthest point (in time) from the Insteon
> control signal. That the triac is being turned off at this point
> is the least likely explanation as the current, being at or near
> maximum, is almost certainly far above the triac's holding current.

When the triac is triggered does it keep conducting until the current
passing though it drops below the holding current or can it be turned off
before the zero crossing is reached?

(As an aside, IIRC, resistors change value when heated.  Do the properties
of inductors change if they get very hot?  I'll bet those teensy little
SwitchLincs get God-awful hot driving a large load with significant
dimming.)

> This is also the area where triac switching noise will be at a maximum.

(Forgive me for breaking your message up like this, I know it's not your
preferred style, but I need line-by-line guidance!)

Why would the switching noise be at maximum?  Because the voltage is at its
peak?  Because there's more area under the curve at the peak for a given
length of time and so there's more current?  Is the noise created harmonic?

> An undersized choke could allow this noise to reach the PIC
> (in the subject switch or in other devices on the line) and this
> might cause the PIC to stutter and miss a half-cycle or more.
> (The PIC has to actively turn the triac on for each half-cycle.)
> Earlier Smarthome designs (e.g. 1132B and 2000STW) have
> been overly sensitive to disruption by out of band noise.

I believe Dan had also mentioned this unwanted PIC interaction as a possible
cause for the flickering.  FWIW, this seems to be the likely explanation
because reports indicate the V2's are emitting EMI that's extending well
beyond the local circuit.  Something's leaking out of the V2's that's strong
enough to fool nearby devices into behaving erratically.  There's not much
other than EMI and voltage fluctuations to explain flickering.   I believe I
read that the EMI placed on the line by a triac is 90 degrees out of phase
with the original AC cycle.  Is that what's causing nearby dimmers to
flicker?

I also read that chokes are selected for dimmer circuits that limit the rate
of rise of current to minimize EMI and that the choke by itself does not
solve the noise problem.  The self-capacitance of the inductor means they
typically resonate below 200 kHz and look like capacitors to disturbances
above the resonance frequency.

(BTW, the odd effect I saw with my dad's shoplite flickering was caused by a
bulb that was on its last legs.  Even the small voltage drop caused by the
charger was enough to destabilize the lamp, which is electronically
ballasted.)

It seem as if the flicker issue is pretty close to resolved.  Now, what
about the flashing/blinking reports?  Would triac noise be able to trigger a
very brief on/off cycle?  It seems to get back to the issue of whether noise
on the line can cause unwanted switch operation.  IIRC, a while back you had
discovered that a big enough spike will cause X-10 switches to cycle without
valid input.  Is that what we're seeing here?

One more stupid question:  Are triacs and thyristors the same thing?

--
Bobby G.