Solar. - Here is Circuit Schematic A Primer on Solar Charge Controls using MOSFET. A primer on solar charge controls. A brief search on eBay turned up some 4700 listings for solar charge controls. Prices on 12 /24V units range from about 7 to $250. With all the specifications and buzzwords that are thrown around, many are understandably confused. This discussion should be helpful in making the best selection.
Low frequency solar charge controls fall into two categories: Relay based and SSS (Solid State Switching). While the relay based control is considered by some a dinosaur, it is actually the workhorse of the industry. It functions by picking up a relay every few seconds and remaining picked up until the voltage reaches the cut-out level, at which time it drops and waits for the next cycle. The SSS control works in similar fashion, but uses a MOSFET instead of relay contacts. The MOSFET has the advantages of being able to work on both 12 & 24V systems, and offers longer life because there are no moving parts to wear out –this is the most common type of control available. They are well suited for charging large batteries at a relatively low rate (e.g. charge time is greater than perhaps 4hours). They are not suited for charging small batteries.
The Original Article: "A Primer on Solar Charge Controls"