Battery Charger with Timer & Tips

Lead-Acid battery requires a long time charging with the moderate current to attain full charge. 24-hour continuous charging is ideal for both lead-acid battery and tubular battery. When the battery first starts to accept a charge, heavy current flows into it during the first one or two hours and then drops to 500 mA or less during the subsequent hours. If the battery is a healthy one, it will not take the current once it attains full charge. The terminal voltage of the 12-volt lead-acid battery rises to 13.8 volts and that of the tubular battery to 14.8 volts in the fully charged condition. If the battery is kept unattended for more than one day, the battery may overcharge which leads to its efficiency loss. The circuit described here is that of a battery charger with a timer to switch off the charging process after 24 hours.

The circuit has three sections

1. Charger circuit

A 14-0-14 volts 2 amperes step-down transformer is used to drop the 230 volts AC to 14 volts AC. The low volt AC is rectified to DC by the diodes D1 and D2 which can handle 2 amps current. The rectified DC is then made ripple-free by the smoothing capacitor C1.

2. Timer circuit

A 24-hour timer circuit is built around IC1 (CD4060) which is a binary counter IC with ripple cascade arrangement. It starts the timing cycle provided its reset pin 12 is low. The IC has 10 outputs which become high one by one depending on the values of the timing capacitor at pin 9 and timing resistor at pin 10. The pulses are fed to the clock input pin 11. Due to binary counting of the IC, each output turns high after a period double than the previous one and the output remains high for that entire period. If the high output is fed back to the clock input through a diode, the IC strops oscillating and the particular output remains high till the IC resets. The reset pin12 is connected to the junction between C2 and R1 so that IC resets at power on and starts oscillating. After 6 hours, pin 1 of the IC becomes high and the Green LED turns on. After 12 hours, pin 2 turns high and the yellow LED turns on which indicates half time. After 24 hours, pin 3 turns high and the relay triggers to cut off the charging process. At the same time, diode D3 conducts and inhibits the oscillation of IC so that the relay will remain energized till the power is switched off. Red LED indicates the activation of the relay and the termination of the charging process. By changing the value of C3 or R3, it is possible to increase or decrease the timing.

3. Relay driver

Transistor T1 is the relay driver. A 12-volt relay is used to provide charging current to the battery through its common and normally connected (NC) contacts. So that when the relay is in the off position, the battery will get charging current, and when the relay triggers, charging will terminate. Diode D4 protects T1 from back e.m.f when T1 switches off.

Battery Charging Tips and Precautions

The lead-Acid battery is a heavy current device and contains sulphuric acid. They are used mostly in automobiles. When a lead-acid battery is charged; electric current passing through the battery causes some chemical changes in the battery as energy is absorbed. When connected to a load, this absorbed energy is released in the form of electrical energy.

It is necessary to take precautions during battery charging to avoid hazards due to sparking, acid spilling, explosion, etc.

16  tips to remember while handling the battery

1. Always keep the battery in a well-ventilated space. The automobile battery should be firmly fixed in the vehicle to avoid shake. Inverter battery should be placed on a wooden plank if possible.
2. The caps should be in space while charging. Always close the caps completely.
3. Fill the battery with ion free distilled water to the required level before charging. Water filling will reduce the space of gas accumulation. Do not overfill water and do not spill water over the battery.
4. Clean the battery surface with a wet cloth soaked in soap water to remove dirt and dust.
5. Before charging, place a wet cloth over the caps. This prevents the sparks from entering into the battery accidentally due to the shorting of terminals.
6. Do not keep any inflammable liquid-like Petrol near the battery.
7. Do not place any metal objects like screwdriver or spanner on the battery. This may cause shorting of terminals.
8. Clean the connectors using a wet cloth. If rust is present, clean it with sandpaper. Always keep the terminals clean for the proper passage of current.
9. The connectors should be firmly attached to the battery terminals.
10. It is better to charge the battery after removing its terminals. Disconnect the Negative terminal first. This avoids the shorting if the positive terminal accidentally makes contact with the vehicle’s body.
11. The charger should be plugged into the AC socket only after it is connected to the battery. This prevents sparking while connecting to the battery. After charging, switch off the charger first and then remove the clips.
12. Rock the charger clips to the terminals to remove any dust or rust. The corroded material may cause resistance that will lead to terminal heating and improper charging.
13. Do not wear any metal bangle or metal wear in the hand while handling the battery. This prevents shorting and burning.
14. Do not look into the battery cavities while removing the caps. The acid may spill if gas escapes through the vent. It is good to wear a spectacle during the water filling. If acid water spills on the eyes, clean many times with pure water, and take medical attention.
15. Observe the battery while charging. If the water boils (bubbles may appear in normal charging) and battery heat up, stop the charging immediately.
16. Use a good quality transformer based charger. For Automobile and Inverter battery, use a 14 volt 5-10 Amps transformer.

I hope you have got an idea about the battery charger with a timer so if you have any further more queries on this topic or from the electrical and electronic projects leave the comments section below.