The NE555 is probably the most popular IC in history. Billions of them are made

every year. I used a 5 Volt regulator. The transistor is a 2N2222. The MOSFET is an

IRFP450.All the resistors are 1/8 watt. The two trimpots, R1 and R2, are ideally multi-turn

unit with a slight loss of precision in the tuning. I used 10K trimpots.

When the circuit was built, it is time to tune or calibrate it. I use 11.9V and 14.1V as

my low and high set points for the controller. These are the points where it switches from

sending power to the batteries to dumping power into a dummy load, and vice versa (A

dummy load is only needed when using a wind turbine. If using only solar panels, the

dummy load line can be left open).

Probably the best way to tune the circuit is to attach a variable DC power supply to

the battery terminals. Set the power supply to 11.9V. Measure the voltage at Test Point 1.

Adjust R1 until the voltage at the test point is as close to 1.667V. Then set the variable

power supply to 14.1V and measure the voltage at Test Point 2. Adjust R2 until the voltage

at the test point is as close to 3.333V. Once the researcher had the circuit working, he

mounted it inside a semi-weatherproof enclosure. Following are some photos showing the

charge controller.