This circuit prevents a battery being overcharged. When the battery is FULLY CHARGED, the energy from the solar panel is dumped into a LOAD. This load can be a 12v 100watt globe or a high-power resistor.
You only have to dump excess current if your solar panel is capable of fully charging the battery in less than 10 hours.
If it takes 14 or more hours of sunlight to charge the battery, this is equal to 2 days of illumination and the battery will accept this low rate of charge and you possibly don't need this circuit.
A simple way of charging a battery without needing this circuit is to put a high wattage resistor and diode in series with the positive line of the solar panel and the battery.
The solar panel will then simply trickle charge the battery over a few days.
SETTING UP
Use a variable power supply.
You don't need the high wattage resistor or the battery or solar panel or the relay!.
Connect the variable power supply set to 11.9v. Adjust the top 10k pot to turn ON the charging LED.
Increase the voltage to 14.9v and adjust the lower 10k pot to make the dumping LED come on.
Now connect all the components as shown in the circuit and check the voltage levels once more before installing the project.
The white LED "jacks up" the 7805 to produce 8.5v output as the 555 does not like a voltage as low as 5v.
To manually "charge" or "dump" energy, simply press either button quickly and the 555 will toggle to the required state and perform the operation of charging or discharging.
If you don't have a variable power supply, here's what you do:
Get a small 12v battery and fit it to the circuit.
It will charge very quickly and you will be able to keep reading the voltage across the battery as it charges. Adjust the HIGH and LOW voltages (called "set points") as close as possible and watch the circuit cycle "up and down."
Each time you see it "cycle" you can fine-tune the exact voltages until you see it change at 11.9v and 14.9v.
In fact you can use any set of old "junk" rechargeable cells to perform this test as you are simply reading a high and low voltage and waiting for it to reach these values over a short period of time.
SOURCE:
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html#M
You only have to dump excess current if your solar panel is capable of fully charging the battery in less than 10 hours.
If it takes 14 or more hours of sunlight to charge the battery, this is equal to 2 days of illumination and the battery will accept this low rate of charge and you possibly don't need this circuit.
A simple way of charging a battery without needing this circuit is to put a high wattage resistor and diode in series with the positive line of the solar panel and the battery.
The solar panel will then simply trickle charge the battery over a few days.
SETTING UP
Use a variable power supply.
You don't need the high wattage resistor or the battery or solar panel or the relay!.
Connect the variable power supply set to 11.9v. Adjust the top 10k pot to turn ON the charging LED.
Increase the voltage to 14.9v and adjust the lower 10k pot to make the dumping LED come on.
Now connect all the components as shown in the circuit and check the voltage levels once more before installing the project.
The white LED "jacks up" the 7805 to produce 8.5v output as the 555 does not like a voltage as low as 5v.
To manually "charge" or "dump" energy, simply press either button quickly and the 555 will toggle to the required state and perform the operation of charging or discharging.
If you don't have a variable power supply, here's what you do:
Get a small 12v battery and fit it to the circuit.
It will charge very quickly and you will be able to keep reading the voltage across the battery as it charges. Adjust the HIGH and LOW voltages (called "set points") as close as possible and watch the circuit cycle "up and down."
Each time you see it "cycle" you can fine-tune the exact voltages until you see it change at 11.9v and 14.9v.
In fact you can use any set of old "junk" rechargeable cells to perform this test as you are simply reading a high and low voltage and waiting for it to reach these values over a short period of time.
SOURCE:
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html#M
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