The following description of the electronics systems typically in use is only a simplistic overview. The various manufacturers have detailed descriptions of their particular units, refer to these for full details. This description only covers the units I have measured. There are others out there that I have not either seen or tested. Listed below are the units I have tested Engelec Max 4 Scorpio Easymax III Automax (became available late 2010) Box Hill High School versions 1,2,3 and 4.
The best general description for the units that I can give is Input Controlled DC to DC down Converter. What does this really mean? It means that the input voltage is controlled, that is held constant at the value you have set which should be just below the maximum power voltage of your panel. An electronics unit that automatically tracks the solar panel`s maximum power voltage was put on the market in November 2010.
By holding the solar panel at its maximum power voltage all the power available from the solar panel is being fed to the motor at all times irrespective of sun level motor speed or load. Whereas without an electronics unit the power fed to the motor is often below the 26 maximum available and varies significantly with changes in sun level, motor speed and load. The DC to DC down convertor means the unit takes in DC power and converts it to DC power at a lower voltage. The voltage out of these units is always lower than the input voltage.
How is this all done?
All the units function in a similar manner. They store energy from the solar panel in a small capacitor (the capacitor behaves somewhat like a small battery) this capacitor is charged by the panel until it reaches the voltage that the electronics unit has previously been set to.
(Just below the panel’s maximum power voltage). The electronics unit then switches power to the motor on till the capacitor discharges slightly (typically by about 1 volt) it then switches power to the motor off till the capacitor charges up again, when the capacitor has charged to the set voltage the unit again switches power to the motor on till the capacitor discharges. This switching process continues.