Outline
A battery is an electrical device that stores chemical energy which can be converted to electrical energy. It is an energy storage device that produces electricity by connecting its terminals to an electrical gadget, appliance or machine. Two broad categories of batteries are; rechargeable and non-rechargeable types. It is key to note that a battery produces direct current voltage only, however one can engage an inverter to change to alternating current. In this article, we will look at one of the rechargeable battery types called lead-acid batteries. The earliest source of electrical energy was a battery and to date, it is still a popular device that one cannot wish away.
construction
As the name suggests this battery is made of an acidic solution called electrolyte and electrodes dipped inside the acid. The two parts are housed in a plastic casing and lead is provided on the top cover to access the solution. The common electrolyte used is sulphuric acid and a pair of electrodes are lead and lead (IV) oxide. A rechargeable chemical reaction takes place between the acid and the electrode producing electricity. As technology advanced the electrolyte is not only a liquid, acidic paste such as silica gel has also been in use. The advantage being it cannot spill out easily and thus battery need not be in a vertical position always.
Working
To produce an electrical current that flows through its terminal to a load, a chemical reaction must take place. There are two states of a battery that is charged and discharged state. For current to be produced, it has to be charged.
Discharging
The process of producing current is called discharging. Sulphuric acid reacts with a positive anode which is made of lead oxide to produce lead sulphate and water.
PbO2 + SO42- + 4H+ + 2e– PbSO4 + 2H2O
On the cathode electrode Lead reacts with sulphate ions to produce lead sulphate and two electrons are released. The free electrons flow from the cathode through the connected circuit to the anode terminal.
Pb+ SO42- 4 PbSO4 + 2e–
As the discharging continues, sulphuric acid concentration reduces and the liquid becomes water. The lead oxide anode is coated with a lead sulphate layer which is a poor conductor. This means that as discharging continues, the reaction rate decreases and in turn current produced decreases. The ideal total discharge state is when all acid has been changed into water and all sulphate ions have reacted with lead to form lead sulphate. This is however not practical as recharging becomes difficult and sometimes not achievable at all. As a maintenance measure, a battery should not be discharged below the 40% level.
Recharging
This is actually the reverse of discharging. The chemical reaction taking place decomposes Lead Sulphate in water into sulphuric acid and lead oxide. For the process to take place a dc voltage is applied between the terminals. The current flowing transports electrons that react with lead sulphate on the cathode producing Lead and sulphuric acid.
PbSO4+2e– Pb + SO42-
On the anode electrode, the current decomposes water molecules into hydrogen and oxide ions which react with lead sulphate to produce, lead oxide and sulphuric acid.
Recharging a battery makes it available to produce electricity thus enabling the recycling of the device. A complete charge and discharge are called a cycle. Batteries can be actively being used for about 3 years after which the electrode and the acid age out and replacement are required. For silica gel non-maintenance batteries, the battery is just disposed of and a new one is acquired. Care should be taken to avoid overcharging a battery.
Maintenance
For safety and efficient operation there are a number of maintenance practices that ought to be observed. They include;
- Keeping terminals corrosion free and well tightened.
- Storing the battery in a well-ventilated room.
- Frequenting recharging the battery even it is not in use (it suffers self-drain)
- Topping up with water when low.
- Physical inspection of the housing for cracks or swelling.
Factors to consider in selecting a battery
You need a battery, cool, how do you go for the one that will serve you well? The device comes in all sizes, shapes and colours, to get it right consider the following;
- Voltage- Voltage is determined by the number of cells. A cell usually has 2.1V output and most batteries have 6 cells. The most common voltage rating is 12V. there is also one with double the voltage rating i.e. 24V. as the need arose, today one can find batteries with ratings of 3V, 6V, 9V and 18V. the voltage requirement of the buyer may not give him a single battery with such input, in this case, the configuration is made to achieve the right voltage. Series, parallel or a hybrid of the two is employed.
- Capacity- this is given in terms of ampere-hours. For example, a battery rated 100AH means it can provide a current of 100A for one hour before it is discharged. The lesser the current drawn from a battery, the more the time it will take to discharge; the opposite is equally true.
- Technology- there is rechargeable versus non-rechargeable, liquid versus gel, lithium-ion technology, design of terminals, size and shape for various needs of users.
- Purpose- solar panel, automobile, uninterrupted power supply, electronic device or big machines. The place of installation should be considered too.
Application
There are billions of devices that use battery supplied dc power to function. These include;
- Motor vehicles- to power engine starter motor.
- Uninterrupted power supply to critical load e.g. hospital equipment, data centre and office computers.
- Solar panel energy storage for night use.
- Mobile equipment that cannot be connected to grid power e.g. entertainment and media automobiles.
- Electric power diesel generators starting system.
Advantages
- It is mobile
- Able to produce high current
- Rechargeable once discharged.
- Low voltage rating.
- Available and affordable in different sizes.
Disadvantages
- Short line-span – about 3-5 years
- Oriented limited to vertical position due to spillage risk.
- Electrolyte is corrosive
- Charging takes time
- The lead electrode used are poisonous and pose a disposal challenge.
Conclusion
The lead-acid battery has been a blessing in the electrical engineering world. It has revolutionised and power industry and brought forth efficiency that cannot be imagined in another way. Since its discovery, it is still in use. You need it, your office desktop needs it, your power utility provider needs it and everyone benefits from it. Hoping the post has given you a green light in your choice of battery. One caution; Never ever try to short the terminals of a battery with a metallic object.