Battery

What is an Automotive Battery?

An automotive battery is a rechargeable battery that supplies electrical energy to a motor vehicle. It is also known as an SLI battery (starting-lighting-ignition) and its main purpose is to start the engine. Once the engine is running, power for the car's electrical systems is supplied by the alternator. SLI batteries are designed to release a high burst of current and then be quickly recharged.

How do the car Battery Work?

Car Batteries are typically made of six cells in a series circuit. Each cell provides 2.1 volts for a total of 12.6 volts at full charge.

A battery cell consists of two lead plates a positive plate covered with a paste of lead dioxide and a negative made of sponge lead, with an insulating material (separator) in between. The plates are enclosed in a plastic battery case and then submersed in an electrolyte consisting of water and sulfuric acid. Each cell is capable of storing 2.1 volts.

In order for lead acid cell to produce a voltage, it must first receive a (forming) charge voltage of at least 2.1-volts/cell from a charger. Lead acid batteries do not generate voltage on their own; they only store a charge from another source. This is the reason lead acid batteries are called storage batteries, because they only store a charge.

The size of the battery plates and amount of electrolyte determines the amount of charge lead acid batteries can store. The size of this storage capacity is described as the amp hour (AH) rating of a battery. Lead acid batteries can be connected in parallel to increase the total AH capacity.

Battery Discharge Cycle

A fully charged battery is connected to a load and the chemical reaction between sulfuric acid and the lead plates produces the electricity to light the bulb. This chemical reaction also begins to coat both positive and negative plates with a substance called lead sulfate also known as sulfation.

This build-up of lead sulfate is normal during a discharge cycle. As the battery continues to discharge, lead sulfate coats more and more of the plates and battery voltage begins to decrease from fully charged state of 12.6-volts. the battery is now fully discharged, the plates are almost completely covered with lead sulfate (sulfation) and voltage has dropped to 10.5-volts. Discharging a lead acid battery below 10.5 volts will severely damage it!

Lead sulfate (sulfation) now coats most of the battery plates. Lead sulfate is a soft material, which can is reconverted back into lead and sulfuric acid, provided the discharged battery is immediately connected to a battery charger. If a lead acid battery is not immediately recharged, the lead sulfate will begin to form hard crystals, which can not be reconverted by a standard fixed voltage (13.6 volts) battery converter/charger.

Battery Recharge Cycle

The discharged battery is connected to a converter/charger with its output voltage set at 13.6-volts to 14.4 volts. In order to recharge a 12-volt lead acid battery with a fully charged terminal voltage of 12.6-volts, the charger voltage must be set at a higher voltage. During the battery recharge cycle lead sulfate (sulfation) begins to reconvert to lead and sulfuric acid.

During the recharging process as electricity flows through the water portion of the electrolyte and water, (H2O) is converted into its original elements, hydrogen and oxygen. These gasses are very flammable and gassing causes water loss and therefore lead acid batteries need to have water added periodically.

One disadvantage of recharging a lead acid battery at a fixed voltage of 13.6-volts is the recharge time is very long. Once a battery reaches 90% of full charge, the voltage must be reduced from 14.4-volts to 13.6-volts to reduce gassing and water loss.

Another disadvantage of recharging a lead acid battery at a fixed voltage of 13.6-volts is that once it is fully charged, 13.6 volts will also cause considerable gassing and water loss. To prevent this from occurring the charging voltage must be reduced to 13.2-volts once the battery reaches full charge. At a charging voltage of 13.2 volts, the converter/charger will maintain a full charge, reduce gassing and water loss.

Automotive Battery  Components

There are a few different kinds of Batteries, but they typically include these basic components:

1. Battery Casing
2. Positive electrode
3. Negative electrode
4. Electrolyte Solution
5. Cell Divider
6. Positive Terminal
7. Negative Terminal
8. Separators