• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Resource icon

Competition (#3) Entry: Solar Powered Night LED’s 2010-08-07

This project uses a lead-acid battery to power some strings of LED’s at night for illumination of my patio. The battery is recharged with a solar panel. The panel is monitored and is used like a photocell to turn on the lights at night and off at dawn. The LED’s energized with a PWM voltage to conserve power.

Theory of Operation

U1 is a three terminal 12V lead-acid charger that requires no external parts for charging the 12V battery. When the power switch S1 is turn on U2 supplies a regulated 9V for the 555 timer IC’s U3 and U4. U3 is used to monitor the voltage of the battery. R1 is adjusted for a nominal battery voltage of 12.6V. This causes U6 the opto coupler pin 4 to be near ground as the discharge transistor in the 555 is in saturation so pin 7 is near ground potential. R2 is adjusted for a discharge voltage of 11.7V. When the battery discharges to this level pin 7 is like a open circuit. Thus Q1, IRF4905 is then turned off.

U4 monitors the voltage on the solar panel. When the voltage drops to approximately 3V, the output pin 3 goes high supplying voltage to pin 1 of the opto coupler. When the battery has a good charge and it is near dusk both the input diodes of the opto coupler are conducting and Q1 is turned on.

When it is dawn the solar panel voltage increases to about 6V and U4 pin 3 goes low, this then turns of one input to the opto coupler, even thou the battery may have a good charge the load is turned off as Q1 is turned off.

The opto coupler works as an and circuit. If the battery is charged and it is dark the LED’s come on. U5 is an astable oscillator to power the LED’s Pin 3’s output changes state approximately every 13mS and is low for approximately 3.4mS. When pin 3 is low, Q2 is turned on and the LED’s are illuminated. I estimate the average current load for the LED terminals to be 200mA.



Parts List

B1 12V 2.6AH Gel-Cell battery
C1 0.1uf
C2 0.1uf
C3 0.1uF
C4 0.1uF
C5 0.1uF
C6 0.47uF
C7 10uF Electrolytic Capacitor
D1 1N757A 9.1V 400Mw zener diode
Q1 IRF4905 P Channel Mosfet
Q2 IRF4905 P Channel Mosfet
R1 100K 20 turn trimpot
R2 100K 20 turn trimpot
R3 2K
R4 1.5K
R5 2.0K
R6 100K
R7 150K
R8 47K
R9 220 ohm
S1 SPST Toggle
SP1 5W Solar panel PowerUp model BSP-512
U2 78L09CA
U3 NE555P
U4 NE555P
U5 NE555P
U6 LTV826 LITEON opto coupler
First release
Last update
3.00 star(s) 1 ratings

Latest threads

EE World Online Articles