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Charging a lead acid accumulator.

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Ogu Reginald

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I want to construct a device that will charge a battery. The mode of operation of the device is: it should start charging the battery with maximum current and later charhges the battery wiith a constant current and when the battery is full, it should prevent thw battery from being over charged by producing a negligible current output. Please can anyone help me with a circuit diagram and tutorials.
 

tpetar

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Tahmid

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Using a microcontroller will simplify the control of the charger, provided you can work with microcontrollers. Control without microcontroller is also possible.

You need to measure the battery voltage and charging current.

Use this algorithm:
When battery voltage < 13V, charge battery with high current (you can charge a 12V battery with 14.5V to 15V to maximize charging current).
When battery voltage reaches 13V, charge battery at fixed current (C/10 maybe). Use a sensor (shunt or hall-effect) to detect charging current and use feedback to keep charging current constant.
When battery voltage reaches 14V, charge battery at 13.5V so that the battery is charged in "float" mode.

For adjusting voltage and current, implement two feedback loops - the voltage loop is activated when battery voltage < 13V and when battery voltage > 14V. In between, the current loop is activated. There will be two reference voltages for the voltage loop - one when battery voltage < 13V and a different one when battery voltage > 14V. The current feedback loop will have a fixed reference.

You could add some hysteresis in the feedback loops so that a loop is "entered" and "left" at slightly different voltages to prevent oscillation between loops. You could also just use a time difference to increase the time between oscillations.

Hope this helps.
Tahmid.
 

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