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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Noisy Space Heater
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. |
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