Bicycle Powered Refrigerator

The generator as mounted on bike.

Brandon Hazon

Summary:

The purpose of the bicycle powered refrigerator is to allow someone to take a bike trip and keep their food or drink cold. Whether just out biking, or on the way to a picnic, the food and drink needs to stay cold. The requirements for the bike are that it must be self powered and it must be able to cool and keep cold whatever is placed in the fridge.

Several different concepts were considered for the generator. The first one had a chain connecting the rotating shaft of the generator to a gear on the bike, so when it was pedaled, the generator received mechanical power. This proved to be faulty because the chain fell off consistently. The second concept used the same generator, but had a 90 degree gear box that mounted near the axle so when the wheel was spinning the generator received mechanical power. The third concept was that of a bike light generator, which has a roller that touches the rim to provide mechanical power. This proved to be the easiest and cheapest concept, and so was chosen. However, this type of generator provided AC power, and DC power was required, so a full-wave rectifier circuit was built.

Once it was determined that a wave rectifier was needed, output values from the generator were needed to determine the value of the capacitor in the rectifier. The bike was flipped upside down and, using an oscilloscope, it was found that the generator produced up to .8 Amps, up to 10 Volts, and had a time period of roughly 0.3 milliseconds. Using the equation C=I L T/2V R , it was thus determined that a capacitor of 10 micro Farads would be an appropriate size to smooth the AC current into a nice DC current.

The fridge was relatively simple in concept, but much more difficult to construct. The concept was a polystyrene box with a hinged lid, a heat transfer plate, a Peltier chip, and a heat sink. The major challenges of this were to attach a hinge and a mounting plate to the fridge, and to fabricate the heat transfer plate. This was accomplished by gluing ¼” masonite to the fridge with contact cement, and then screwing the hinges onto the masonite. The heat transfer plate was bent so that pop cans could rest in the bend and have constant contact with the plate to improve heat transfer.