On Feb 13, 6:51 pm, Paul M. Eldridge
wrote:
Thanks. I had only a sketchy understanding of how this technology
works so this helps me considerably. And given these thermostats are
connected to resistance loads that should happily work with pretty
much anything you throw at them, they most likely lack any
sophisticated circuitry, as you suggest.

Which brings me to this question: these thermostats are becomming
increasingly popular and they do work extremely well from a consumer's
point of view, but I wonder what impact they may have on power
quality. I understand triacs can generate some nasty THD numbers; one
thing to dim a 60-watt incandescent bulb but 6,000 watts of electric
heat has to kick things up a notch or two. Any thoughts?
....

That's at least theoretically true -- to what extent it is a real
problem I don't know -- it's not quite as bad as a chopped DC in terms
of the generated harmonics and not as much of a problem from high
frequency as a switching power supply owing to the base 60 Hz
frequency, but I don't have any real information at hand on what sort
of problems one might cause in the practical sense.

As I noted in another response, the noticeable effect w/ dimmers is
owing to the small inertia of the filament so that flicker can be
visible and "singing" may sometimes be heard. That's not nearly as
likely w/ the heaters so unless there's something nearby that is
susceptible to the radiated harmonics (AM radio is one likely
candidate, perhaps), it shouldn't cause too much problem. Large
heaters like you're talking about tend to be on dedicated circuits so
there isn't as much likelihood of direct contamination of some
sensitive input supply.