In this topic, you study charging a battery.
There are two ways to charge a battery as
(a) When D.C. available?
(b) When A.C. is available?
When D.C. is available
The D.C. voltage may be available in two conditions the low voltage and high voltage.
(i) D.C. low voltage. In this case of low voltage the battery is connected across the supply through suitable controllings. As in case of cars, trucks etc. the shunt generator in used. In this case the positive of the source is connected with the positive of the battery and negative with the negative of the battery. If more than one batteries are to be charged then the batteries are connected in parallel.
(ii) D.C. high voltage. If voltage D.C. is available then the constant current method is used and a battery charging board is used. The number of carbon filament lamps are used to control the current. The lamps are so connected that they are in parallel to each other and in series with the battery as shown in Fig. 9.13. The number of lamps of a given wattage to be connected can be calculated as:
N = The number of lamps.
I = The charging current in ampere.
E = The supply voltage in volts.
Eb = The battery voltage in volts.
W = The wattage of the lamp in watts.
Disadvantage. This method is not useful if the batteries are less in number because the power loss in the lamps will be merely a wastage.
When A.C. is available
In this method the batteries are charged by the following ways:
(i) By means of M.G. set. In this set the a.c. motor is coupled with d.c. generator. The motor is energised by a.c. supply and it drives the d.c. generator hence d.c. is produced. The d.c. voltage is used for charging the battery at a constant voltage method. It is costly and requires more maintenance.
(ii) By means of battery charger This method is mostly and commonly used nowadays. The battery charger has a step down transformer so a low voltage is obtained and converted into d.c. by means of the rectifier. The rectifier can be the metal rectifier or bulb rectifier.
Metal rectifier. In this method a selenium or copper oxide rectifier is used. The property of the oxide layer is to allow the current in one direction and check in the reverse direction. Figure 9.14 shows the connections of a bridge rectifier used for battery charging.
In bulb rectifier the A.C. is converted into D.C. by means of a tunger bulb rectifier. Figure 9.15 shows a full wave tunger bulb rectifier. There are two anodes and one cathode which emits the electrons. The electrons are attracted towards the positive plate (anode) during one complete cycle. The anodes are alternatively attracts the electrons and full wave is rectified. The voltmeter and ammeter connected indicates the voltage and current for charging the battery.
Fig. 9.14. Bridge Rectifier
Fig. 9.15. Tunger bulb rectifier.
Advantages of battery charger. There are the following advantages:
- Power loss is less.
- It requires less maintenance.
- Requires less attention during charging.
- Easy to handle and connections are also easy.
What precautions should be observed while charging a battery?
The following precautions are observed during charging and before charging a battery:
- The charging voltage should be higher than the battery full charged pd.
- The cell must be charged on D.C. only. The positive of the battery is connected with positive of the source and negative with negative of the source.
- The level of the electrolyte must be 10 to 20 mm above the plates. To maintain the level of the electrolyte distilled water is added.
- The electrolyte should not contain any impurity.
- The vent plugs must be opened.
- Charge the cells as per rate and instructions supplied.
- The connections must be tight, right and cleaned.
- The battery charging room must be well ventilated.
- Don’t bring any naked flame near the place where the battery is being charged because hydrogen gas is flammable. The jars of acid and distilled water must be properly marked.
- A battery must be recharged as soon as it is discharged otherwise the sulphation will take place and the battery would not be in a position to be recharged.