In this topic, you study the different methods of Charging a battery.
There are two main methods of charging a battery:
Constant current method. In this charging method the batteries are charged at a constant current. The charging current is set by introducing some resistance in the Circuit. This method has its own drawbacks because the state of charge Of the battery is not taken into account. Initially the charging rate may be high but when the battery is charged up to some extent the charging rate will be less.
Constant voltage method. In this method the batteries are charged at a constant voltage. The voltage is given to the battery by means of the d.c. shunt generator or rectifier. With this charging method the time of charging is reduced considerably.
According to the charging rate, the charging is of the following types:
(a) Initial charging. It is the first charge given to the new battery after purchasing. In this charge, the battery is charged at a low rate, generally 2 A. While putting on charge the makers instructions and battery conditions must be strictly followed.
(b) Normal charging. In this type of charging the battery is charged at normal rate generally 4 to 6A. This charging is suitable for the batteries working in normal conditions and having no defect.
(c) Boosting charging. Charging at a high rate is known as boosting charging. The maximum limit of the charge is six times the normal charging rate. It is suitable for the batteries which are normal and are required in short time.
(d) Trickle charging. This charging is done at a very low rate, i.e. even 1/50th Of the normal charging rate. It is applied when the battery has not been used and lying idle.
(e) Equilizing charging. This charging used to remove the sulphation from the plates. In this method the low charging rate is used, which is generally 1/4th of the normal charging rate.
What are the indications of fully charged and fully discharged battery?
There are the following indications:
(a) Gassing. When a battery is put on charge and it is fully charged, the gassing takes place. The gassing is because the current is not used for battery charging but decomposes the water and gases are released.
(b) Specific gravity. Measure the specific gravity of the electrolyte three or four times. The specific gravity in fully charged condition is between 1250-1280 and during completely discharged condition 1150-1180.
(c) Potential difference Of each cell. In case Of fully charged condition the voltage per cell will be between 2.2 to 2.5 V per cell. But after sometimes the voltage falls to 2.1 V/cell. When this stage is reached the battery is fully charged.’ In no case the discharged p.d. should be less than 1.7 V/cell.
(d) Colour of the plates. In case of fully charged battery, the colour Of the positive plates is chocolate brown colour and Of negative plate is grey colour.
(e) Level of electrolyte. In case of fully charged cell the level of electrolyte should be 10 mm to 20 mm above the plates. But it decreases from the initial level in fully discharged condition.
