The Universal Basic Differential Controller or BDC can be used to
regulate either AC or DC pumps for solar heating. A DC powered pump shares a common
junction with the controller. This is done by placing a jumper between pins
2 & 3. In other words a PV panel with a battery backup can be used to power
both controller and pump. An AC powered pump does not require a jumper
between pins 2 & 3 but it does require a tiny DC supply to power the
controller. This BDC can regulate pumps up to 300 Watts, but it consumes
less than 1 Watt per hour.