Battery Manager with Computer Control

Figure 1 

The project is intended for typical rechargeable batteries used by R/C devices, various consumer product batteries, and electronics hobbyists.

The circuit consists of five portions made of logic power, voltage measurement, battery connection, current control, and power supply.

A commercial off-the-shelf- model of power supply is used to provide 18V at 2.2A but any similar power supply can be used with the capability of producing 18V to 20V. The control of current comes from the constant current flowing into the collector of Q3. The CMOS buffers together with resistors to form a ladder digital-to-analog converter with a resistor adjusting its output voltage range from 0V to 0.2V. The four low-order data bits of the parallel printer port provides the input to the converter.

The positive terminal of the battery being charged connects or disconnects using a transistor and a relay. The battery gets disconnected when the bit of the parallel port is low or otherwise gets disconnected when high. When the positive battery terminal is connected to the collector of Q3 and the negative terminal to the ground, it will discharge the battery since any current flowing though Q3 will come from battery.

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