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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;

1. Keeping terminals corrosion free and well tightened.
2. Storing the battery in a well-ventilated room.
3. Frequenting recharging the battery even it is not in use (it suffers self-drain)
4. Topping up with water when low.
5. 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;

1. 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.
2. 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.
3. Technology- there is rechargeable versus non-rechargeable, liquid versus gel, lithium-ion technology, design of terminals, size and shape for various needs of users.
4. 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

1. It is mobile
2. Able to produce high current
3. Rechargeable once discharged.
4. Low voltage rating.
5. Available and affordable in different sizes.

Disadvantages

1. Short line-span &#; about 3-5 years
2. Oriented limited to vertical position due to spillage risk.
3. Electrolyte is corrosive
4. Charging takes time
5. 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.

If you are looking for more details, kindly visit Features Of Sealed Lead Acid Batteries.

Lead Acid battery downsides

1/ Limited &#;Useable&#; Capacity

It is typically considered wise to use just 30% &#; 50% of the rated capacity of typical lead acid &#;Deep Cycle&#; batteries. This means that a 600 amp hour battery bank in practice only provides, at best, 300 amp hours of real capacity.
If you even occasionally drain the batteries more than this their life will be drastically cut short.

2/ Limited Cycle Life

Even if never drain your battery too much, the best lead-acid batteries last only 500 to cycles. If you are frequently tapping into your battery bank, your batteries may need replacement after less than 2 years use.

3/ Slow & Inefficient Charging

The final 20% of lead acid battery capacity can not be &#;fast&#; charged. The first 80% can be &#;Bulk Charged&#; by a smart three-stage charger quickly (particularly AGM batteries can handle a high bulk charging current), but then the &#;Absorption&#; phase begins and the charging current drops off dramatically.

Just like a software development project, the final 20% of the work can end up taking 80% of the time.

This isn&#;t a big deal if you are charging plugged in overnight, but it is a huge issue if you have to leave your generator running for hours (which can be rather noisy and expensive to run). And if you are depending on solar and the sun sets before that final 20% has been topped off, you can easily end up with batteries that never actually get fully charged.

Not fully charging the final few percent would not be much of a problem in practice, if it wasn&#;t for the fact that a failure to regularly fully charge lead acid batteries prematurely ages them.

4/ Wasted Energy

In addition to all that wasted generator time, lead acid batteries suffer another efficiency issue &#; they waste as much as 15% of the energy put into them via inherent charging inefficiency. So if you provide 100 amps of power, you&#;ve only storing 85 amp hours.

This can be especially frustrating when charging via solar, when you are trying to squeeze as much efficiency out of every amp as possible before the sun goes down or gets covered up by clouds.

5/ Peukert&#;s Losses

The faster that you discharge a lead acid battery of any type, the less energy you can get out of it. This effect can be calculated by applying Peukert&#;s Law (named after German scientist W. Peukert), and in practice this means that high current loads like an air conditioner, a microwave or an induction cooktop can result in a lead acid battery bank being able to actually deliver as little as 60% of its normal capacity. This is a huge loss in capacity when you need it most&#;

The above example shows specification of Concord AGM battery : this spec states that the battery can provide 100% of it&#;s rated capacity if discharged in 20 hours (C/20). If discharged in one hour (C/1), only 60% of rated capacity will be delivered by the battery. This is direct effect of Peukert losses.

At the end of the day, an AGM battery rated for 100Ah at C/20 will provide a 30Ah usable capacity when discharged in one hour as 30Ah = 100Ah x 50% DoD x 60% (Peukert losses).

6/ Placement issues

Flooded lead acid batteries release noxious acidic gas while they are charging, and must be contained in a sealed battery box that is vented to the outside. They also must be stored upright, to avoid battery acid spills.

AGM batteries do not have these constraints, and can be placed in unventilated areas &#; even inside your living space. This is one of the reasons that AGM batteries have become so popular with sailors.

6/ Maintenance Requirements

Flooded lead acid batteries must be periodically topped off with distilled water, which can be a cumbersome maintenance chore if your battery bays are difficult to get to.

AGM and gel cells though are truly maintenance free. Being maintenance free comes with a downside though &#; a flooded cell battery that is accidentally overcharged can often be salvaged by replacing the water that boiled off. A gel or AGM battery that is overcharged is often irreversibly destroyed.

7/ Voltage Sag

A fully charged 12-volt lead acid battery starts off around 12.8 volts, but as it is drained the voltage drops steadily. The voltage drops below 12 volts when the battery still has 35% of its total capacity remaining, but some electronics may fail to operate with less than a full 12 volt supply. This &#;sag&#; effect can also lead to lights dimming.

8/ Size & Weight

A typical 8D sized battery that is commonly used for large battery banks is 20.5&#; x 10.5&#; x 9.5&#;. To pick a specific 8D example, Trojan&#;s 8D-AGM weighs 167lbs, and provides just 230 amp-hours of total capacity &#; which leaves you with 115 amp hours truly usable, and only 70 for a high discharge applications!

If you are designing for extensive boon docking, you will want at least four 8D&#;s, or as many as eight. That is a LOT of weight to be carting around that impacts your fuel economy.

And, if you have limited space for batteries on your rig &#; size alone of the batteries will limit your capacity.

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