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Author Topic: Using an intentional infinite loop as a failsafe  (Read 938 times)
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Pittsburgh, PA, USA
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But where's the fun in that ?

The fun of look, I didn't have to over-engineer and over-budget something simple?

A car radiator valve has more muscle but needs a lot of heat to open.
Thing is, it can open the vent hatch with the fan switch attached.
Downside, they cost more new than a bi-metal coil from a junk yard and I wouldn't trust an old one.

If you want to get creative, make something that uses waste heat to power the fan(s).

Or maybe a stovepipe with baffles would just draw the hot air out without too much noise,
when a vent does open it's going to get loud anyway.


And I'm the one who's over-engineering?  What exactly do you think a "radiator valve" is, anyway?

From back before there were microprocessors a car radiator valve was mainly two layers of different metals fused together in a housing with valve flaps. They had no power connections yet were strong enough to hold against pump pressure, more than strong enough to flip a switch and off the shelf solidly automotive-standard reliable.

Please understand that I'm more concerned about the expensive piece of machinery that are trying to protect.

You might even look at an analog temperature sensor wired to an Arduino-compatible relay through a resistor and transistor. The relay triggers, on goes vent opener and fan. 
« Last Edit: March 28, 2013, 04:43:14 am by GoForSmoke » Logged

I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

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From back before there were microprocessors a car radiator valve was mainly two layers of different metals fused together in a housing with valve flaps. They had no power connections yet were strong enough to hold against pump pressure, more than strong enough to flip a switch and off the shelf solidly automotive-standard reliable.

I've never seen a thermostatic valve like that.

Almost all thermostatic valves are operated by a cannister full of wax which expands with heat and drives a pin out - the pin is mechanically connected to a flap to seal/divert the coolant. A heavy spring keeps the wax under pressure and pushes the pin back as the wax cools and contracts. On some modern cars the cannister includes an electrical heating element so that the operating point can be varied by an electronic controller.

The bimetallic device you describe sounds like what is often called an 'otter switch' and is simply used to make/break an electrical circuit to operate the fans - it does not generate any significant mechanical force and doesn't directly operate anything mechanical. These have largely been phased out in favour of simple relays driven directly from an ECU.

What is being proposed here could be implemented trivially easily using a couple of otter switches, but I gather the OP wants to use a microcontroller.
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