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The charging current is used to recharge reusable batteries by converting chemicals into stored electricity. Lead-acid batteries can suffer from sulfation, but pulse charging can help restore them. Charging current should be regulated to prevent overheating. Nickel metal hydride and lithium ion batteries require separate charging. Capacitors can also be charged and used in electronics.
When a reusable battery loses its stored charge, it can be recharged by applying a charge current that converts the chemicals in the battery into stored electricity. The battery stores this charge until it is needed again, when the reverse chemical reaction releases the electricity stored in the battery. The charging current is what allows the battery to be used repeatedly, and how the current affects the battery depends on the chemicals used in it.
Lead-acid batteries are widely used in transportation, solar energy storage and other applications that require large electrical storage capacity. These batteries consist of a series of lead plates preserved in a mixture of sulfuric acid and water. A chemical reaction occurs between the lead and the acid and an electric current is produced. Each cell in a lead-acid battery creates about 2.2 volts, so a 12-volt battery will have six cells and a full charge of slightly more than 13 volts.
When a lead-acid battery is repeatedly discharged or ages, the reaction of lead and acid creates lead sulfate, which can eventually coat the lead plates and cause the battery to fail. Proper charging current can reverse part of this reaction, called sulfation. Technology developed in the late 20th century, called pulse charging or pulse width modulation, can largely reverse sulfation and restore good electrical capacity to older batteries.
Charging current should be carefully controlled or regulated, as too much power sent to a battery will cause it to overheat. Hot batteries not only have a lower charge capacity, but they can also fail if water boils or evaporates from excess heat. Many battery chargers use charge controllers to reduce the current flow when charging the battery, and some may control the battery temperature to prevent overheating.
Smaller rechargeable batteries, including nickel metal hydride and lithium ion batteries, can, in some cases, be recharged. Nickel hydride batteries are sensitive to charge current and if a weaker battery is placed in a charger with more powerful batteries, they may not accept a charge properly. Many of the chargers contain circuitry that charges each battery separately, rather than combining them into one circuit. Separate charging allows each battery to receive a specific current to optimize its charging.
Charge current also refers to the electrical power required to charge a capacitor. A capacitor is a solid-state device containing two plates made of a material that can conduct or pass electrons. The two plates are separated by a dielectric material, which resists the flow of electrons to some extent. When the capacitor is charging, current flows across a plate, creating an excess negative charge. At the same time, the opposite plate is developing a positive charge.
This stored electrical charge acts as a battery and can be stored for long periods of time. When a switch connects the capacitor to an electrical circuit, electrons pass through the dielectric and into the positively charged plate, creating a flow of electricity. Electric current will flow until the capacitor is discharged, at which time it can be repeatedly recharged. Capacitors are used extensively in electronics to provide several functions including voltage and power control.
