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1w Solar Path Light Using COB LED - May 23, 2017

Chip on board (COB) LEDs are all the rage.  These devices assemble multiple tiny LED chips onto a metal backed circuit board, then cover the assembly with a plastic cover.  The metal back allows the assembly to be mounted to heat sink to keep the device cool.  The multiple LED chips can be wired into any number of series/parallel configurations.  Some are wired for 12v operation while other COB LEDs in flashlights are all wired in parallel, with an operating voltage of about 3 volts.  The COB assembly produces a light source with a broad illumination pattern from a flat device.


3W 3v 16 LED COB Light Strip

You can buy COB strips on eBay.  But I used a COB strip from a flashlight I bought at dollar store one day. I counted 16 LEDs inside the COB assembly, all wired in parallel.  I removed the light strip and tested it.  It had a forward voltage of about 2.9v with a current of 300ma.  Although the flashlight drives the COB LED much harder, I thought I would try to keep the LED current to about 300ma for a 1 watt dissipation.

For a solar panel, I selected a 10 cell solar panel with an output of about 600ma.  For a battery, I wired 6 AA NiMH cells in a series/parallel circuit for a 3.6v 5 amp-hour pack.  I used a cheap solar path light I bought from a home improvement store.  I removed the guts from the path light and used a scrap piece of black plastic to hold two pieces of the square tube light assembly together.  I mounted the solar panel to the top half of the light.  I mounted the COB light strip to a 1/16 thick copper sheet, then mounted the sheet to the side of the lower part of the path light tube.  The circuit board and battery pack mounted inside the square light tube.  The copper sheet made an excellent heat sink, keeping the COB LED cool. 

I really liked the finished prototype.  It emits a very bright and broad light pattern on the path in front of the light.

COB Flashlights From Dollar Store

Prototype Solar Path Light Prototype Solar Path Light
 

Click on Drawing Below to view PDF version of Schematic


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