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FLOAT_CHARGING_CIRCUIT

2014-11-21 02:39  
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FLOAT_CHARGING_CIRCUIT
To float-charge a 12-V lead-acid battery, all you need is an accurately regulated 13.8-Vdc power supply. You could connect the power supply directly to the battery, but it is safer to make the connection through a couple of 12-V, 1-A automotive light bulbs. The light bulbs serve as current limiters; they guarantee that no matter what happens, the power supply will never have to deliver more than 2 A. Resistors can also serve as current limiters, but light bulbs are better because their resistance varies with current in a useful way. It's nearly zero at low current, but as the current through each bulb approaches 1 A the bulb lights and the resistance increases. Thus, the bulb limits the current, but doesn't waste energy when the current is low. This setup is a good way to power a heavy load that operates intermittently, such as a ham radio transmitter. The battery delivers heavy current when necessary and the power supply keeps the battery charged.