Simple Shunt Solar Controller 1A

by Alan K Biocca, WB6ZQZ (wb6zqz at ARRL.net)


Requirements:

  Simple, Low Parts Count
  Adjustable voltage setpoint
  Hysteresis
  Adequate for Panels up to 100 watts or so (depending on heatsinks)
  No RFI (Radio Frequency Interference)

Design:

  The simplest designs are based on a shunt controller and a Schottky
  diode. The shunt FET shorts the panel out when the battery voltage
  gets high enough. The Schottky diode has a low forward voltage drop
  during the charge phase, and prevents current from the battery flowing
  back into the panel during darkness or the FET during shunting.

  Power is dissipated in the Schottky diode during charging, and in the
  FET during full-charge shunting. Assuming the pcb area can dissipate
  1 watt, the design doesn't need heatsinks up to about 1 amp, or perhaps
  2 amps. The Schottky diode will dissipate more than the FET. Above 
  about 1-2 amps a heatsink is required. The maximum current for these
  parts is about 7 amps, giving a safety margin under the 10 amp rating
  of the schottky diode. A higher current diode can be fitted, but larger
  heatsinks will be required to go to higher currents. The FET is rated
  at 20 amps (depends on temperature) but will be dissipating perhaps
  30 watts at that current.

  Voltage Hysteresis is provided by the brownout-reset IC.

PCB:

  The printed circuit boards were designed using free software from
  www.expresspcb.com. They have a low cost miniboard service that costs
  under $70 and provides six boards. The design places two layouts on one 
  pc board, and the service provides three of these dual boards. The user
  must cut the boards in half.

  If you want the PCB download the software from www.expresspcb.com.
  You can then view the pc layout, and order boards direct from them
  via the net.

-- Alan
