A BATTERY CHARGING ALGORITHM FOR A MODIFIED PWM - CONTROLLED SOLAR CHARGE CONTROLLER

Presented in this study is a development of a pulse width modulation (PWM) battery charging algorithm for a solar charge controller. The solar charge controller developed in a product-quality packaging in this work was based from an existing circuit design which was modified by the researchers for reasons of extended functionality, added protection, flexibility in control and more comprehensive display. The developed algorithm was designed primarily to prevent the overcharging of a 12-volt car battery, i.e., preventing to charge the battery beyond the absorption voltage level set in this work to 14.4 volts. Also included in the functionality of the charge controller is its ability to prevent the battery from deep discharging, i.e., preventing a connected lighting load from drawing power from the battery when the latter's voltage is below 12 volts. A bi-modal liquid crystal display was employed to show two related groups of infor1nation related to the charge controller's operation with a pushbutton provided to toggle from one display mode to the other. Several experiments were conducted purposely to validate the voltage and current measurements of the charge controller using three multi-testers which are of the same brand and model. Experiments to validate that the PWM algorithm is effective in preventing to overcharge the battery were also performed. Results show that even without software calibration, the multi-testers show readings within 5% accuracy in voltage readings and within I0% accuracy on current. Also, the developed algorithm was shown to effectively adjust the duty cycle to a proper value every 500 milliseconds successfully preventing the battery to be charged beyond 14.4 volts.