joachimp at gmail.com
Fri Feb 12 07:48:32 UTC 2010
So, 555timers are really small ICs, which can't really push that much
current, so you would need to have the 555 trigger some kind of power
FET methinks. Also, resistive heating is notoriously inefficient...
So how about some chemistry? The crystallization of sodium acetate
creates quite a good amount of heat, it whats used in reuse-able
heatpacks! Whats better, is that the reaction can be triggered by
something like a servo connected to a uCtrler that monitors the
internal temperature. We just need to substantially disturb the
solution! We could have several cells of sodium acetate solution, and
activate them in sequence as more heating is needed.
How long is the flight time? I assume you just need to stay above 0C?
Is there data on the temperature history during last flight? Any ideas
on a target max weight for the heating system?
On Thu, Feb 11, 2010 at 21:29, Jonathan Moore <moore at eds.org> wrote:
> On Thu, Feb 11, 2010 at 9:04 PM, Christie Dudley <longobord at gmail.com> wrote:
>> Nichrome seems to make sense if we were going to go with electric heat,
>> which is probably a good idea for keeping the camera lens defogged/frost
>> free. I wouldn't want to use it for much else, and also probably focusing
>> on trying to get thermally insulative materials whenever possible. (Which
>> means aluminum is right out.)
> Well If insulation is enough but for longer flights we might need
> something more.
>> What would the purpose of the 555 chip be, though? I don't think the
>> nichrome would work with PWM very well, although I might be mistaken. Then
>> you'd have to have a circuit to drive the 555 and...
> Yes I was thinking PWM, I see no reason why that would not work. 555
> circuits are super simple.
>> I understand a thermistor, if well-positioned, could be instrumental in
>> controlling the current, but if you have a well-designed circuit to limit
>> current flow, wouldn't the thermistor be all you need? What would the
>> circuit you have in mind look like?
>> Possibly using it in a wheatstone bridge or some other tuned simple circuit
>> could be employed to good effect to run the nichrome, don't you think?
> I don't really know. The thing about PWM is you could have it
> basically 100% if you did not need the heat.
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