My friend and I have started this project. We are simply going to use a solar panel (max 16V output at 140 to 180 ma) to maintain a 12V lead acid battery's charge. I am planning on using a circuit based on an LM3914 bar graph driver IC. I found a simple circuit that I plan on modifying for my use (**broken link removed**. I'm going to chage some resistor values around to make it sensitive from 11 to 14 volts instead of the values given in the diagram. To signal whether to charge the battery or not, I'm planning on using a transistor triggered by LED 10 (100% charged) turning off. However, this is where my problem arises.
From what I know, the battery will float between the voltage required to light LED 9 (90% charge) and LED 10 (100% charged). As soon as LED 10 turns off, the power from the panel is directed to the battery, and the battery's voltage will rise. Eventually, this rise will reach the the voltage required to turn of LED 10, stopping the charge. As the battery charges more and more, this process will repeat at a fast rate (charge on, charge off) thus causing the switching transistor to get hot. I know I'm not switching much current (less than 200ma) but at a fast switching rate, won't it heat up the transistor? Will this be a problem with the design if I choose to use a high rated transistor (like 5 amps?)? What other possibilities do I have to remedy this?
Sorry for typing so much...I tried to summarize it as much as possible. Hopefully you get the gist of whats going on.
Also, we're on a somewhat limited budget, so thats why no microcontrollers are involved. Otherwise, I would have done it that way and it would have been MUCH easier.
Thanks in advance,
Dan