More  Solar Cell Circuits

Solar Powered Tool Shed LED Light -- July 14, 2017
designed by David A. Johnson, P.E.

I have a lean-to 8ft by 12ft shed next to my house.  It is full of lawn chemicals and garden supplies.  There were times when I needed to get something from inside the shed during the dead of night.  Early on I had to use a flashlight.  But later, I installed a series of five 12v LED light strips on the ceiling.  Each strip contained 15 3v white LEDs.  The strip had 5 strings of three LEDs, wired in series, with a 150 ohm current limiting resistor.  Each 12 inch strip drew about 100ma or about 1.2 watts per strip.   Up to 6 strips can be powered by the drive circuit shown below for about 4 hours of illumination.  A single push-on/push-off switch turns on and off the lights.

A rechargeable battery pack is created using ten 1.2v 2.5AH AA NiMH
cells wired in series.  The 10 series cells form a 12v pack with a 2.5AH rating.  An automotive type solar panel is mounted to the roof of the shed charges the battery pack.  Wires leading from the panel are routed to a junction box (pictured right) containing the battery and switch.  A single Schottky diode is wired between the solar panel and the battery to prevent current back-feed to the panel from the battery at night.  No other electronics was needed.

I suggest charging the pack with a 2 watt 12v solar panel with a minimum of 28 cells.  Many panels designed to maintain the charge of a car battery are ideal.