Hello friends

Thank you for your support for my previous project

Today I am going to make life hack "instructable" can save both money and time. This is the tutorial of “how to make an automatic solar powered night light”. This device can charge at daytime and work automatically at night

Step 1: Know Your Circuit

This device has three circuits. a switching circuit. a solar charging circuit with battery and a LED night light circuit

Step 2: The Switching Circuit

Switching circuit is most

important part in this system. to make the switching circuit you need

1) IRFZ44 MOFSET

2) 150K Ohm resistor (see the step 3 for more details)

3) 3 2pin PCB connecter

4) Wires

5) LDR

6) PCB BORD

Fig shows the circuit

I am using a long two core coated wire to connect the LDR to main circuit. it will help to avoid the unwanted lights from other light sores

Step 3: Calibration of the Circuit

This is the most important step

in the circuit designing. Calibration of the circuit helps to improve the sensitivity of the dark sensor

LDR is the important component of this circuit. it will act as the dark sensor. There are two methods to calibrate the LDR one pre calibration and other one is post calibration

In pre calibration we use a single resistor with pre calculated resistance. in post calibration we use a variable resistor and calibrate circuit at final stage

I am using pre calibration just because of its simplicity in India cost of a variable resistor are 5 to 10 times higher than a single resistor

For pre calibration you need to find the right resistor. For this first you need to find R max and R min of the LDR

Connect your LDR to multicenter and find the maximum resistance(R max) at day time. Repeat the step at night time and find out the minimum resistance(R min)

In my case R max is 600k and R min is 2k

To find the resistance we need I am using voltage divider equation

V out = V in x (R2/R1+R2)

V out = voltage to MOFSET Gate

V in = supply voltage (12V)

R1 = R min (2K or 2000 Ohm in my case)

R2 = R1 (I am using 150K or 150000 Ohm resistor)

12x (2000/2000+ 150000) = .150V

That means the MOFSET will stay off

Now test with R max .it is 600K or 600000 Ohm

12x (2000/2000+ 600000) = 9.5V

So the MOFSET is turn on and it switch on the light

Step 4: "Power, Light and Charging"

I am using a 12v 7Ah battery as

power source and a 12v 2W LED as light source. To charge the battery i am using 12v 6W solar panels. to reduce the cost i am using a DC to DC buck converter as charge controller. it can boost 12v to 14v and prevent reveres flow of voltage with a high capacity diode

You may wonder how this circuit work without any overcharge protection

After the one month test run i found out that these solar panels can’t fully charge the battery. Due to low current, battery needs 18 hours to fully charge the battery but sunlight is only available for 12 house max. in conclusion at the night time the switching circuit and LED light consume 10 to 12w of power from battery and at day time the solar panels refill the battery. Little bit tricky but its work!

Step 5: Fitting and Wiring

The fig shows the circuit of whole system

Step 6: The Moment of Truth

If everything is correct the circuit switch on the light at night and switch off and charge at the battery at day time. Just fix everything on a safe place and it work automatically