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Circuits designed by David Johnson,
P.E.
Last Updated on:
Monday, December 25, 2017 02:08 PM
Master Category List - Dave's Circuits
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More
Solar Cell
Circuits,
LED (Light Emitting Diodes) Circuits
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Improved Solar LED Spot Light
February 1, 2013 |
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Nearly all the Chinese made solar
powered LED lights I see being sold at Lowe's and Home Depot home improvement centers
are poorly designed. Their solar panels and battery packs are all undersized.
The light from their Chinese made LEDs fade rapidly and the devices never make it
through a complete night before the light dies. I have been buying some of these
poorly designed devices and modifying them, so they perform to my satisfaction. In
this example, I gutted the Lowe's spot light device shown below and installed proper
components. |
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I first replaced the original single dim T 1 ¾ size LED with a brighter,
longer lasting part made by Cree. The undersized solar panel was peeled away from
the top of the assembly and replaced with a larger 5v 150ma solar panel. I used some black
caulk to hold the panel in place and to seal it from the weather. The original small
250ma-hour lithium ion battery was replaced with a larger 2200 ma-hour cell. I removed the
original control board and replaced it with a more efficient circuit design shown below.
That circuit used a low voltage drop battery charge controller IC to insure the lithium
battery was charged properly to a voltage of 4.2 volts. I then used a LED current control
circuit which only had a 0.05 volt drop. That circuit used a single low power op
Amp. Finally, I used the voltage developed across the solar panel as a day/night
sensor, turning on the light only when the solar panel voltage dropped to a low level.
The result was a light which was much brighter and lasted for several days, even under
cloudy conditions. |
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Original Light |
10
cell 5v 150ma Solar Panel |
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3.7v 2.2 Amp-hour Lithium Ion Cell |
Cree White LED |
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Click
on Drawing Below to view PDF version of Schematic |
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