Monday, February 6, 2017
Battery Charging Test
The objective for the first 2 weeks of this semester was to test charge the batteries and ensure functionality. Due to weather conditions being rainy and cloudy generally throughout the past 2 weeks, the only window I've found to test the equipment was on Saturday and Sunday. First, I began by checking the voltage of the combined 6 cell battery. The battery's initial voltage was 7.56V.
After about roughly 3 hours with numerous resetting of the charging unit, the voltage of the battery was 8.10 V. These resets were caused by dense clouds or other obstacles preventing the solar cells from producing enough power which results in a voltage drop across the circuit. Due to these resets, the time period of charging is unknown. Future plans will feature a recording device so that the exact time when charging stops will be known. The specifications for the iMAXB6AC states the allowable DC input voltage is 11-18V. The buck converter was set to 17.9V, the highest allowable voltage output (input into iMAXB6AC) to delay the "DC IN TOO LOW" error message which stops the charging process because of the insufficient sun light. According to the manual this error is caused by the input voltage being less than 11V.
Without any battery voltage charge chart, it is difficult to determine the state of charge (SoC) of the battery as the relationship between voltage and SoC is exponential. Only references I found for 7.2V nominal batteries were stating that a fully charged battery would measure ~8.4V. The goal of the next testing session is to determine the maximum voltage the batteries will reach and time it takes to reach this maximum voltage.