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Appendix D, Power Sources

Table D-7. Li-Ion cells

Cell type Voltage Capacity Size

1865 3.6 1600–1700 mAh 65mm × 18mm (diameter)

1767 3.6 1300–1320 mAh 67mm × 17mm (diameter)

Prismatic 3.6 800–1400 mAh 34mm × 50mm × 10mm

This extra capacity and light weight come at a price. These batteries are

much more expensive that NiCad and NiMH cells and require special

charging circuits.

Many companies now make Li-Ion cells, including Sony, Sanyo, and

Panasonic.

Solar Cells

Electrical power can be generated from light sources using a photovol-

taic cell (also known as a solar cell). These are available from a variety of

sources, including Radio Shack and DigiKey.

Each solar cell typically provides a low output voltage, 0.6V, and produces

energy only when illuminated. In order to provide energy under both light

and dark conditions, some sort of battery and charger connected to the solar

cells must be used. This allows the cells to charge the batteries for use when

there is no light source. It also evens out the power provided by the cells due

to changing light conditions.

With careful design, small panels can typically power a low-power micro-

processor by themselves.

Generators

Electrical power can be derived from mechanical work using a generator. A

number of simple generators are readily available for the hacker.

Bicycle generators

You may remember as a kid having a light on the front of your bike that was

powered by a small metal “bottle” that rubbed against the side of one of the

tires. This bottle was a small generator. You can still obtain these generators

for a relatively low price, anywhere from $10 to $30. The output of these

generators is an AC waveform that must be converted to a DC voltage if you

want to use it for anything other than powering a light bulb. Small bicycle

generators typically provide only a few watts of power.

Generators

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Part III: Appendixes

Wind-up generators

A number of companies offer flashlights and radios powered by a small

generator turned by a wind-up spring mechanism. A company called

Freeplay (http://www.freeplay.net/) offers wind-up radios, flashlights, and

generators.

Generators

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