Thermoelectric Generator Mobile Phone Charger

electronic projects

Attention! This device wasn't tested in field's conditions!
Today is a lot materials about thermoelectric chargers for mobile phones (for example: http://overland-botsman.narod.ru/termogen.htm it's in russian). I think that this type of power source can be useful for outdoor application.

For start building this source I wrote such equation:
P=W*Keff; where P - power for charge (useful power)
W - thermal flow through Peltier modules
Keff - efficiency of Peltier modules in generator mode, 2-3%
This means the following:
If we need in 3W power we must have 100W thermal flow through Peltier modules. Of course, campfire can give bigger thermal power, than 100W (until 1-5kW), but cooling modules… It is the problem. Air cooler for 100W is massive thing. As variant of solution of this problem is water cooling. In this situation we have light, small size generator (about 110-130 gr) and the need for pipes, tanks (bottles) and water.
Volume of water flow is:
heat capacity of water is Cp = 4.1855 [J/(g·K)] (15 °C, 101.325 kPa), real value of delta T between out/input of cooler is 10-20K, therefore - Mwater(100W)=W/(Cp*deltaT), g/sec; Mwater=100/(4.1855*20)=1.19 g/sec ~72 g/min ~ 4.3 L/hour. If use 2l bottles it needs add water to bottle every half-hours. It don't look like at very horrible.
Be careful, without water flow Peltier modules will be damaged.
See at this conclusion, I built thermoelectric generator that give 340mA of charger current to mobile phone at temperature 120°C of hot side and 40°C of cold side. For that I use 2 Peltier modules 30x30mm dimension, 128 thermocouple every. Weight of device is 120-130 g. Converter is buster with maximum point power tracker features and output voltage limited on 5.6V (ATtiny85 control chip).

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