Ideation, the buzzword for this week. Start breaking down the idea, coming up with initial concepts, researching the problem within the problem. Sketches, soft models, prototypes, anything to show the formation of the project. With my idea being based around science, rather than an aesthetics / reboxing project, I needed to start with proving the science; proving that the concept – a head torch powered without the need for mains electricity or disposable batteries – could work.
As a basic starting point, I wired up the thermoelectric generator to a multimeter, placed my hands on the ‘hot-side’, and recorded the readings – 0.17 volts. Not a massive figure, but enough to show that they work. Phew. Two generators added more voltage, but didn’t double it. Placing the cold side onto frozen peas made a big difference. The bigger the differential in temperature, the more voltage produced. If I can get the hot-side super hot, or the cold super cold, we’re onto a winner. Placing the two units on the forehead produced about 2.3volts, which isn’t enough to run an LED bulb, but was again, promising. Whacking the generator cold-side onto an old computer heatsink, certainly made a difference, so materiality will be a large factor in the efficiency and effectiveness of the product.
How to improve this? What tech is out there that I can hack? Solar powered garden lights. They’re only 85 pence (!), have a rechargeable battery inside, along with a solar cell and possibly, some kind of ‘joule thief’ or ‘low voltage booster’ (more on this in a mo). The solar cell, on a dim afternoon, produced about 2volts of juice. Way more than the thermoelectric generator. [Aside: I am already sick of typing that long phrase, so from now on, will be called Gens.] The working principle of trickle charging a rechargeable battery, rather than directly feeding the LED is a good one. The battery can charge in the daylight, and then discharge when darkness sets in; lasting around 8 hours for one LED. Not too shabby. If I can trickle charge the battery with heat – albeit, at a slower rate – the principle still works.
As a prototype, I added the Gen as an additional power source to the solar light, hot glued it to the back of it, and relocated the LED to the front of the unit. The solar cell can charge the battery in the day, then at night (darkness), the head torch can be put on and the Gen can continue to top up the battery as it is depleting, extending the battery / LED runtime. The little blighter works. It straps to the head fine, provides enough illumination in the darkness to be able to read a book or operate a simple machine, and should hold power for several hours. The biggest hurdle will be to stop the Gen from getting universally warm – i.e. both sides of the plate becoming saturated with heat, meaning no differential of temperature, resulting in no volts. Cooling will be key. I hope that at night, the body will be warmer than the outside temperature, but this may not always be the case.
So how do we boost the volts from the Gens? Using something called a ‘joule thief’ or ‘low voltage booster’. As the later describes, it boosts the voltage of something low powered – by reducing the current I believe – thusly turning 0.2 volts into something that could power an LED. Hopefully, with a couple of Gens, adequate cooling and a joule thief, we should be able to power an LED via the heat of the human body.
To demonstrate this principle to the group, I cut together a video of this testing process and produced my initial prototype. The video mostly makes me look like an idiot, but shows the science works. Good times.
Coming next week: Soldering, LED’s and rubber bands. All in another exciting episode of,
Term Three Blog : Raiders of The Lost Blog