In automotive two different voltage systems are used, 6 volts and 12 volts. In this article, I will discuss how to charge a 12-volt car battery simply.
How to Charge A 12-Volt Car Battery
When a battery is discharged and is not capable of delivering any current, it may be recharged. This is done by supplying it with a flow of current from some external source, such as a generator, which forces current through the battery in a reverse direction. Thus, the plates are restored to their original composition and the battery becomes recharged. it is then ready to use.
Although a generator is always provided in the automobile which is constantly recharging the battery, however external recharging becomes necessary. The rate of charging current from the generator to the battery depends upon the time to charge the battery. The use of car radio, heater, parking light on for longer periods, etc., are the reason that discharges the battery to the extent that requires external recharging.
Charging Procedure
1. Check the level of the electrolyte in the battery. If it is below the top edge of the plates, add more electrolytes so that the level is about 10 mm above the top edge of the plates. Also, note the specific gravity and temperature of the electrolyte.
2. Connect the negative and positive terminals of the battery to the respective terminals of the battery charger. The battery charger is simply a source to supply direct current.
3. Adjust the value of the charging current. This is usually kept half, in amperes, of the number of plates in the cell. For example, for a 17-plate battery, the charging current would be 8.5 amperes.
4. Continue the charging till the gassing begins, then decrease the charging current and continue till there is no further increase in the specific gravity of the electrolyte and cell voltage reading from three hours.
5. If the temperature of the electrolyte during the charging process exceeds 45^0C, discontinue the charging for some time so that it cools to normal temperature. Then again start the charging.
6. Check the specific gravity of the electrolyte hourly during the charging process.
7. Avoid overcharging which may damage the battery, particularly the positive plates.
A battery generally takes 12 to 20 hours for recharging, depending on the charging rate and condition of the battery. The battery with Sulphate plates requires a low charging current and hence takes a longer time for charging. Several batteries may be charged simultaneously if they are connected in series. After the charging, we need to check the state of the charge.
Checking the State of Charge
The specific gravity of the electrolyte is the most common check for the state of battery charge. Cell voltage is also measured to indicate the state of the battery charge. The following readings of specific gravity are the general indication for the charged battery:
| Battery Condition. | Specific Gravity (at 27^0) |
|---|---|
| Fully charged. | 1.230 |
| Half discharged. | 1.175 |
| Fully discharged. | 1.10 |
Note- Specific gravity of the fully discharged battery is less than that of the fully charged battery. During the discharge process, water is produced due to a chemical reaction that dilutes the electrolyte, reducing in specific gravity.
Slow rate and quick rate of charging
The batteries may be charged either by slow rate or quick rate charging method. The slow-rate charging method takes 12 to 20 hours for charging a battery, while the quick-rate charging method tasks about half an hour only.
Ordinary batteries are charged by the slow-rate charging method. It is a safe method but takes a long time for charging. The quick rate charging method takes much less time. High charging current is passed in the battery till it comes to about 80% charge level, after which the current is reduced to a low value. While charging by this method, the battery requires a careful watch continuously so that it may not be damaged.
However, if a battery is in good condition, it should not be charged by this method.
Ending this up
A fully charged battery is a good sign for the driver while starting or driving a car. If you like this article then please read the others it will boost your knowledge of the automobile industry.
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