On Fri, 09 Nov 2012 20:01:00 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Sylvia Else fired this volley in
:

Such circuits typically prevent current from flowing at all within a
half cycle, until a point is reached where the remainder of the half
cycle would deliver an amount of energy that would, if delivered over
the entire half cycle, represent the desired power. Once triggered, the
triac conducts until current drops below some smallish threshold.

A circuit designed to do that with a sine-wave is going to be somewhat
thrown by an input that is a modified sine-wave.


I'm fully aware of how SCR and Triac (or generically, Thyristor)
"dimmers" function, and how to build them (from scratch, without any
supplied schematic).

I'm also aware that a "modified sine wave" or "simulated sine wave" would
satisfy the needs of most of that type of circuit, with the exception
that the initial triggering and the the subsequent "near zero"-crossing
cutoff might occur late and early, respectively, from where they ought.

Such circuits don't work nicely on square waves, primarily because they
don't have time to properly turn off. There's usually some capacitance
in the gate circuit (sometimes driven by a diac) that prevents a very
rapid change from full voltage through zero to the opposite polarity
from lasting long enough below the quench voltage for the device to turn
off.

Such _can_ be the case with a simulated sine wave, where the voltage
might go from (say) +10V-0--10V on a square edge. But most inverter
companies realized a long (long) time ago that doing it that way causes
problems, so they switched (pun) to a waveform that stays at zero long
enough for such devices to turn off properly.

Only a really old, or really cheap Chinese inverter would not have that
feature. For all I know, he has both AND a cheap Chinese blanket that
didn't take into consideration the problems it might see on old Chinese
inverters.

But it's not the case that simulated sine wave inverters universally
cause problems with thyristor switches.

LLoyd
What he NEEDS is a 12 volt blankie. My baby brother has been a long
distance trucker across north america, from Alaska to Florida - and
has 12 volt mattress warmer and 12 volt electric blanket for YEARS.

Lost 'em both when he rolled the truck last year. Bust his neck too,
but he's back on the road - doing mostly short haul flatland driving
hauling crude - less than 2 years after the crash.