When the battery voltage drops below 12 volts, Zener turns off and the regulator again provides charging current. Fast Charger with Cut Off Circuit Schematic Fast Charger with auto cut off. Setting ...

This voltage drop is exacerbated by the high 20A load current rating. For instance, a very good MOSFET switch has a Rdson of 0.016Ω while a good relay offers only 0.005Ω contact resistance – the ...