Creating electricity from heat

generatorlow-power

I want to build an alarm for my soldering iron that goes off if it is hot for too long. Rather than rely on batteries I am wondering if it is possible to generate enough power from the heat of the soldering iron itself.

The device only needs to function when the iron is hot, and it does not need to start right away. The micro controller I using can operate from 2.8V to 5V. It will use 25µA most of the time in sleep mode, only waking up once a second to use 15mA for about 2ms.

I have already confirmed that I can run the MCU from a capacitor using such a small amount of current.

By my estimate it will use ( .002 seconds * .015A ) + (.998 seconds * .000025A) = an average of about ~ 55µA draw.

If it has been on for too long it will make a quick chirp every second. If the iron gets cold it should run out of power and lose its state thus resetting the timer.

My question is can I create enough current to run the chip in sleep mode and charge a capacitor enough to have to do brief awake times using only the heat from the iron?

Best Answer

As a soldering iron is very hot, thermoelectric generators should easily be able to produce enough power from that. You should be careful, that the generator doesn't get too hot, they have a specified maximum working temperature, so maybe you need a block which dissipates some of the heat.

You will need a power supply circuit, as the voltage of the thermoelectric generator won't fit to your microcontroller.

Energy harvesting power management ICs offer most of the features you want for a project like this, with automated charging of a supercap and outputs which tell you what source is currently powering your circuit.

As concrete product recommendations are rather useless in an answer, I'll just suggest you have a look around at Linear Technologies, they offer some nice solutions for this.

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