Current boost for solar panel water pumping

[Opera House]

Found this interesting circuit for extending the time a solar panel pumping system without a battery would operate. The control electronics raises the panels operating voltage closer to the panels power point.

http://www.voltscommissar.net/minimax/minimax.htm

Primary consideration was simplicity and cost and only the input voltage is monitored.  Solar panel current should be sized appropriately for the motor.  Motor is not protected from over driving motor. Still, this may let you get away with a smaller panel with longer pumping times.

[Ungrounded Lightning Rod]

The description of the operation is slightly wrong.

The diode across the motor isn't just to spike-suppress.  The system is actually a switching regulator trading voltage for current.  The motor doubles as the inductor and the "protective" diode is actually the free-wheeling diode.

With the motor stalled the current through it, and thus the torque it exerts, climbs until limited by the resistance of the winding, wiring, and voltage drop of the freewheeling diode.  (If it were a superconductor and the diode ideal it would climb forever - or until the motor started.)