I'm coming around to the "probably not worth including a control circuit" point of view myself. It might be fun to play with the idea but having conducted a thought experiment about how it might work I envisage all sorts of issues with hysteresis etc. A simple fan purring away constantly will probably be good enough.
Nick
There are gadgets that might do what you want without any faffing around:
... and a continuous purring is less intrusive than on-off-on-off...
If you use a large "silent" computer fan, it may come with a temp sensor thing that could be nudged to run faster at about room temperature. Or drive the fan with a voltage proportional to the temp difference? So no hysteresis, just mumble-to-12 Volts?
I also bought a thermocouple-powered fan, similar to:
There's a bimetal strip inset into a groove in the base that tilts the unit back if it overheats; I thought that a simple solution to a non-trivial problem.
Simple and Just Works, in that it helps mix the rising hot air a little more quickly.
Thomas Prufer
Logic would dictate blowing it up might be easier but I feel in practice that the inefficiencies in such systems might make it rather academic in the long run. I've never have thought that doing as you suggest would work anyway though as for there to be e a good mixing the differences need to be big. Brian
Agreed, and you don't even need thermistors. The probes containing the DS18B20 digital temperature chip are amazing. You can hang any number on a single digital input. You just need one pull-up resistor for the lot (and can get away without that). Similar price to a thermistor and none of the faff.
I've thought about adding one of them to my woodburner, the elegance appeals to me (although I suppose I *ought* to prefer a Stirling engine: no electrics at all).
I think puling/pushing hot air down to where you need it would be the preferred option.
I would blow hot upper air down.
If you suck at the bottom end it'll pick up any dust hanging round at low level, then blow it out all over the room.
Owain
Good points, well made from you and Fred but I'd mention that if people became aware of a draught or a cloud of dust then the thing would be running too fast. The idea is just to gently turn over the air in a continuous process so that hot and cold mix to form an even temperature. A fan-assisted oven is not a good simile since that turns the air over with a vengeance!
Nick
Even if you're not aware of a cloud of dust, it doesn't mean that there isn't a cloud of dust.
Owain
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