I was just wondering what the minimum and maximm charging voltage and ampere is for li ion batteries. If i connect a solar panel, which only gets enough sunshine to generate voltage, will that still charge the battery, or would i have to series connect solar panels until they together reach 3,7volt?
One lithium cell requires 4.2V to obtain its full charge, Never exceed 4.2V ! Output from solar panel if below 3.7V , nothing charge to lithium. Total charging time until the cell is full depending on the AH rate of cell and the charging current that solar panel can be provided. Suppose cell is rate 5AH, and the charging current from solar panel under full sun shine can maintain 0.5A ( use solar panel short circuit current rate from its specification as a reference ) , hence, 0 hours is enough. And be sure the solar panel can maintain 4.2V output at 0.5A . Remember, over charge lithium cell one time might reduce its life into half . Therefore, let the solar panel output passing through a precision regulator to maintain output is 4.2V is the best way, because, as cell reaches 4.2V , no more charging current is forced into cell ( automatic stop charging ). If you do not have the knowledge to make this simple variable voltage regulator with LM37K ( if you choose this way, buy solar panel output has at least 2V) , you may choose to do it manually by install a current meter and a variable resistor in series between the panel output to cell. By adjust the value of resistor, charging current can be controlled ( if you choose this way, buy solar panel output has as less as 6V ). Count the charging time with a clock and adjust the charging current from time to time to maintain 0.5A .
