Reading Light Not Quite Powered By Your Favorite Hot Beverage

Thermoelectric devices are curious things, capable of generating electricity via the Seebeck effect from a temperature differential across themselves. The Seebeck effect does not produce a huge potential difference, but when employed properly, it can have some useful applications. [MJKZZ] decided to apply the technology to build a reading light, powered by a hot cup of coffee.

The build is based around four Peltier modules, 40mm x 40mm in size, sandwiched between a pair of copper sheets. The modules are wired in series to create a greater output voltage, and an aluminium heatsink is fitted to one side to create a higher temperature differential. The set-up produces just 230 mV from human body temperature, but over 8 volts when warmed directly with a heat gun. Boiling water in a mug produces a more restrained 2.1V output.

On its own, this voltage is a little weak to do anything useful. Thus, the electricity from the Peltier modules is fed through a joule thief, which helps step up the voltage to a more useful range to run an LED. With a mug of coffee on the copper plate, the assembly isn’t quite able to light the LED enough to allow the user to read comfortably. However, it flickers into life just a touch, demonstrating the basic concepts in action.

While it’s not the most practical build, and it’s likely to cool your coffee faster than you’d like, it’s a fun project that serves to educate about the mechanics of the Seebeck effect and using Peltier devices to generate it. Another fun application is to use them in a cloud chamber. Video after the break.

13 thoughts on “Reading Light Not Quite Powered By Your Favorite Hot Beverage

  1. Well if you put a nice cold can of beer under there you could probably get more light but if I want some illumination from my beverage I’ll just drink a gin and tonic under a blacklight, blacklight blackout, the only way to fly.

  2. Something to try next time you’re out in the boonies or in a power outage or whatevs, get ur trusty koolatron or coleman 12V powered cooler, the car power adapter for it, a car adapter for your phone/usb car adapter, and one of those 2 or 3 into one car power outlet expanders. Plug both your charger and the cooler lead into it, boil a big pot of water by whatever expedient method, (maybe drain your radiator into it (carefully!) if you just fetched up at the side of the road with a dead car and dead phone) on your propane BBQ, campfire, camp stove etc, then pour it into your cooler (beer out first, natch) and see if you can get volts out to run the charger and charge your phone. Think you’d need the switch on cooler set to cool. A reasonably good USB car charger has a switchmode adapter in it that will probably work from 7V up.

    1. I’ve tried to read & understand your text but 6/8ths only contain two full stops (.) -> Following those two sentences is too much of a hassle (for me).
      I think the gist is using a 12V pelitier cooler box in reverse with the still hot coolant of a wrecked car or something to charge a phone…

      1. I fear the result of being exceptionally more lucid in clarity, quality, intelligibility of writing in case I get press ganged into composing and writing articles, when my time is already fully absorbed as editor of the Guardian (Joke)

    2. You won’t be able to sustain any reasonable of power as it is limited by the amount of heat removed by the heatsink inside the unit. It is build with just enough capacity to overcome the heat leaking in through the insulation. The temperature difference decreases and so will be the output.

  3. Interesting and somewhat disturbing that so many are happy to quote open-curcuit voltages for devices such as this, seemingly with implicit assumption that this alone is sufficient to quantify the energy. 2.1 volts ain’t really enough to do anything useful, eh? Perhaps an article explaining these fundamentals would be worthwhile.

  4. “On its own, this voltage is a little weak to do anything useful.”
    Naturally, this was meant to indicate a weak power (voltage + current), not a weak voltage alone? Funny that the article describes power but only mentions voltage. Because e.g. 100A at 1V is still 100W.

  5. Good start – now wrap the modules around the entire outer surface area of the cup and maybe a lid for completeness to up the output.

    Enjoy your rapidly cooling beverage by the fading light…

  6. Basically, that video is more of an educational exercise than anything else. It actually shows how to make a joule thief, how and why to use a joule thief, it also shows what peltier device is, etc. I will have another video coming to confirm what Great Scott (a well known Youtuber) found to debunk another Youtuber’s claim — it is not very practical to charge your phone using peltier device and a candle, yet you can charge your phone, but at about 50mA rate, it will take ages.

  7. A Finnish coffee company made an interesting mug https://www.youtube.com/watch?v=QfhIzMh2I9A . My company worked on the electronics and later a couple of us got some mugs to hack around with. The mug has a peltier element, MCU, bluetooth and an e-ink display. We had our mugs connect to a RasPi in the office and display stuff like cryptocurrency tickers. Would be a fun and useful project to revisit.

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