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Circuits designed by David Johnson, P.E.
Last Updated on: Monday, July 11, 2016 01:59 PM

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Solar Cell Monitors

  • Solar Insulation Monitor
    An inexpensive PIN photo diode and a 1ma meter movement form a simple sunlight intensity monitor.  The sensor should be placed inside a lightly frosted glass hemisphere to minimize the influence of the sunís angle on the sensor.  An adjustment resistor calibrates the meter for a full scale reading under a one sun condition.  An unshielded two conductor cable links the sensor to the meter movement.  The sensor and meter can be separated by up to 200 feet.

  • Solar Powered Lithium Ion Battery Charger
    This circuit is for a solar powered white LED with automatic activation in the dark. It can be used for both indoor and outdoor night light applications. For indoor uses, if the circuit is operated near another lamp, it can be set to automatically turn on when the other lamp is turned off. Circuit features include selectable off/on/auto settings, a built-in low voltage disconnect circuit for longer battery life and a light activation circuit with hysteresis.
  • Solar PV cell Test Fixture
    This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current.  Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions. A halogen incandescent lamp is used as the light source.  (added 7/06)
  • Solar-Powered Pump Motor Controller
    A Discover Circuits visitor had a problem.  He needed a simple on/off controller for his solar powered water pump.  His system used two 12v 50 watt solar panels wired in series.  The power from the solar panels drove a submerged water pump.  However, during overcast skies the pump motor did not operate properly due to the lack of power from the panel.  He wanted a circuit which would turn off power to the motor during low sun conditions.  The circuit below performs this function.  A small 0.1Ē x 0.1Ē photodiode monitors the sunlight intensity.  The current from the diode is proportional to sunlight intensity.  An adjustable load resistor across the diode converts the current into a voltage and feeds the to a voltage comparator circuit.  The output of the comparator drives a small n-channel MOSFET, which in turn drives a high current p-channel MOSFET, controlling power to the pump motor.  When the sunlight is less than one fourth of full intensity, power to the motor is turned off.
  • Visible Light Blocking Filter
    This isnít an electronic circuit but the drawing below shows the curve for an optical filter made from exposed color film. The material blocks most visible light but is very transparent to 880nM infrared light. Kodak 100ASA is exposed to "cool white" fluorescent light for about 5 seconds.

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