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Datasheets : Alternative Power Sources - Power Supply Unit
What does it do?Non-rechargeable batteries are widely used but they cause environmental damage. Alternatives include: USB power from computers, solar power, hand cranked power, recycled old mobile phone chargers and fuel cells. Rechargeable batteries and supercapacitors are also more environmentally friendly and are described in separate data sheets. What’s the Problem?People in the What are the Alternatives?Many people have access to a computer with a USB socket. This can be used to power electronic systems and to refresh rechargeable batteries and supercapacitors. Solar panels convert sunlight to electrical energy. A hand crank can power a dynamo to produce electrical energy. Fuel cells are relatively expensive. They use hydrogen as a fuel to produce electricity. The notes below explain how each of these alternatives to disposable batteries can be used. USBThe USB port of a computer provides a reliable 5V supply able to source 100mA. This is sufficient to power small electronic systems or to recharge batteries or supercapacitors. The connections for series ‘A’ plugs (generally used at the computer end of a USB wire) and sockets are: Connections on the plug at the end of a USB cable
Connections looking into the plug at the end of a USB cable and the device socket on the computer
From the table above, as you look at a USB port on a computer (assuming the visible metal connectors are underneath (as shown above right) the left-hand connector is +5V and the right-hand connector is GND (0V). As we are simply using the USB port as a power source, we can ignore the data lines (connectors 2 and 3).
None of the major suppliers of components to schools seems to stock the cable end USB connectors. However, the 0.1” spacing between the tracks on Veroboard (stripboard) is the same as the spacing between the connectors on the USB socket – and Veroboard is just the right depth to slot into the connector. The same result can be achieved using tracks of the correct width and spacing (0.3”) on a PCB. The USB port can supply up to 100mA and is protected against short circuits. Solar PowerSolar cells convert light energy to electrical energy. They can be used to power small electronic systems or to refresh rechargeable batteries or supercapacitors.
The MUTR EL1 006 produces an output of up to 4.4V and 90mA.
It is important to be aware of safety issues before recharging batteries. To find the actual current output of a solar cell you need to experiment with a multimeter. Hand-cranked Power
An interesting approach using LEGO® components to create a charger for devices powered by USB is described at Instructables.com LEGO® hand-crank – from Instructables Recycled mobile ’phone chargers
Provided the power requirements of the circuit can be fulfilled these chargers can be a cheap or even free source.
Fuel cells
In a basic fuel cell hydrogen and oxygen are combined to create water; this is a chemical reaction that releases energy and the cell is designed to use this energy to separate charges creating a voltage of about 0.7V. The main difference between a fuel cell and a battery is that when the hydrogen in a fuel cell runs out the cell can be refuelled by adding more hydrogen (the oxygen used come from the air). It is worth noting that the chemicals used fuel cells have to be made in some way – usually using electricity generated by some other (usually unsustainable) method. However fuel cells are useful for situations where electrical power is wanted away from mains electricity; in portable consumer goods and for transport. Increasingly you will find fuel cells replacing batteries in products such as mobile phones. There appear to be few options currently available for education to explore fuel cell technology.
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The Rapid 42-0240 produces an output of up to 3V and 100mA. 
Hand-cranked power can be used to recharge commercial radios, torches, phones etc. However the core winding units to achieve this don’t seem to be available to education users.
A good alternative to batteries is old mobile ’phone chargers. The plug that fitted into the ’phone can be removed and replaced with a suitable plug to fit an appropriate socket on the circuit board.
