About the Battery...
12 Volts
The battery for this assembly had to be compatible with the solar panel. Since most of the solar panels are designed to produce 12 volt power the battery had to also be 12 volts. The battery type I chose to use is commonly found in emergency light fixtures, alarm modules and uninteruptable power supplies. It is a lead-acid, sealed, valve regulated gel cell battery. That translates into low maintenance. I recommend selecting a battery that comes with the push-on connector type terminals to simplify do-it-yourself wiring.▼
4 Amp-Hours
12 volts is, of course, the same voltage your car battery uses. The difference is that the smaller the battery the less amount of time it will be able to deliver power without requiring recharging. So the challenge is in figuring out how large your battery needs to be. The longevity of a battery is indicated by its amp-hour rating which is analogous to a car's mileage rating, or miles per gallon. To get some idea of what size battery is appropriate you simply add up the amperages of all the devices you plan to power with the battery. In my case the amperages of the camera, the wireless transmitter and the charge controller add up to 145 milliamps, or 0.145 amperes. A battery rated for 4 amp-hours can deliver 4 amperes for 1 hour. It can also deliver 0.145 amperes for 27.6 hours without recharging. That's sufficient to power the camera overnight when there's no sun available for recharging. But what would happen if when the morning comes the sky is full of storm clouds and the amount of available sunlight is minimal? How long will the camera continue to receive power before the battery becomes damaged by deep discharging? That depends on the size and efficiency of the solar panel and the capabilities of the charge controller. The larger and more efficient the solar panel the more charging power it will be able to generate from minimal available sunlight. And some types of charge controllers called peak power trackers are able to maximize the conversion of solar energy into power by self-proportioning the panel voltage and current. But peak power trackers are generally much more expensive than typical solar power charge controllers. These are the variables that must be considered when deciding on a battery size. In closing I must mention that since obtaining the battery shown in these photos I've discovered that batteries by other manufacturers are available in the same size, and at approximately the same cost, with a 5 amp-hour rating. Why not maximize the life span of the battery if it can be done without requiring more money or space? I now have one of these 5 amp-hour batteries installed on this project which increases the unrecharged life of the power source to 34.5 hours.▲
