This is perhaps a bit off-topic, but this seemed like the best place
to post this question. I bought a fairly expensive Vornado space
heater, it's a rather nice unit with digital temperature control etc.
but it has a rather annoying flaw. You see, instead of controlling the
output temperature by switching separate heating elements on or off
(like most heaters), instead it uses a TRIAC circuit similar to a
light dimmer. While this might allow more precise control over the
heat, it produces a very irritating buzz - much louder than your
average light dimmer, and so annoying that I can't even stay in the
same room. It appears that the buzz comes from the elements
themselves, which are receiving a (presumably) badly-chopped AC
waveform when operating at less than full power. My theory is that if
the AC supply to the heating elements is rectified and filtered, the
buzz should be greatly reduced if not eliminated. Trouble is, we're
talking a 15-amp circuit here, so it will require some very rugged
components. I have some 25-amp industrial rectifiers and plenty of
large heatsinks to mount one on, but what about filtering? I've got
some 200 volt, 1200uF electrolytics I could use, but I'm concerned
about one thing: ripple current. I'm concerned that the ripple from
such a heavy load may be too much for the cap(s), but I don't know how
to determine just what size caps would be needed for this job. I don't
think the elements need a pure, 99.9% filtered DC voltage..... just as
long as the waveform is at least as smooth as standard AC. Then
there's the added problem of the 41% voltage gain when rectifying to
DC, which may require some rather large resistors. Fortunately, the
heater has lots of space for these extra components.
This not only has to work but it has to be safe enough to leave
unattended, as I plan to use it for heating a small greenhouse.
Thanks for any advice.