Definition
A battery charger is a device used to put energy into a secondary cell or (rechargeable) battery by forcing an electric current through it.
Basics
See also Rechargeable Batteries
The charge current depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 V car battery will be very different from the current for a mobile phone battery.
A simple charger works by supplying a constant DC power source to a battery being charged. The simple charger does not alter its output based on time or the charge on the battery. This simplicity means that a simple charger is inexpensive, but there is a tradeoff in quality. Typically, a simple charger takes longer to charge a battery to prevent severe over-charging. Even so, a battery left in a simple charger for too long will be weakened or destroyed due to over-charging. These chargers can supply either a constant voltage or a constant current to the battery.
A trickle charger is a kind of simple charger that charges the battery slowly, at the self-discharge rate. A trickle charger is the slowest kind of battery charger. A battery can be left in a trickle charger indefinitely. Leaving a battery in a trickle charger keeps the battery "topped up" but never over-charges.
The output of a timer charger is terminated after a pre-determined time. Timer chargers were the most common type for high-capacity Ni-Cd cells in the late 1990s for example (low-capacity consumer Ni-Cd cells were typically charged with a simple charger). Often a timer charger and set of batteries could be bought as a bundle and the charger time was set to suit those batteries. If batteries of lower capacity were charged then they would be overcharged, and if batteries of higher capacity were charged they would be only partly charged. With the trend for battery technology to increase capacity year on year, an old timer charger would only partly charge the newer batteries. Timer based chargers also had the drawback that charging batteries that were not fully discharged, even if those batteries were of the correct capacity for the particular timed charger, would result in over-charging.
Fast chargers make use of control circuitry in the batteries being charged to rapidly charge the batteries without damaging the cells' elements. Most such chargers have a cooling fan to help keep the temperature of the cells under control. Most are also capable of acting as a standard overnight charger if used with standard NiMH cells that do not have the special control circuitry. Some fast chargers, such as those made by Energizer, can fast-charge any NiMH battery even if it does not have the control circuit.
Some chargers use pulse technology in which a pulse is fed to the battery. This DC pulse has a strictly controlled rise time, pulse width, pulse repetition rate (frequency) and amplitude. This technology is said to work with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries. With pulse charging, high instantaneous voltages can be applied without overheating the battery. In a Lead-acid battery, this breaks down lead-sulfate crystals, thus greatly extending the battery service life.
Inductive battery chargers use electromagnetic induction to charge batteries. A charging station sends electromagnetic energy through inductive coupling to an electrical device, which stores the energy in the batteries. This is achieved without the need for metal contacts between the charger and the battery. It is commonly used in electric toothbrushes and other devices used in bathrooms. Because there are no open electrical contacts, there is no risk of electrocution.
Since the USB (Universal Serial Bus) specification provides for a five-volt power supply, it's possible to use a USB cable as a power source for recharging batteries. Products based on this approach include chargers for cellular phones and portable digital audio players. They may be fully compliant USB peripheral devices adhering to USB power discipline, or uncontrolled in the manner of USB decorations.
Solar chargers employ solar energy. They are generally portable. Most portable chargers can obtain energy from the sun only. Portable wind turbines are also sold. Some, including the Kinesis K3, can work either way.
Charge rate: This is often denoted as C and signifies a charge or discharge rate equal to the capacity of a battery in one hour. For a 1.6Ah battery, C = 1.6A. A charge rate of C/2 = 0.8A would use two hours, and a charge rate of 2C = 3.2A would use 30 minutes to fully charge the battery from an empty state, if supported by the battery.
Applications
Most mobile phone chargers are not really chargers, only adapters that provide a power source for the charging circuitry which is almost always contained within the mobile phone. They are notably diverse, having a wide variety of DC connector-styles and voltages, most of which are not compatible with other manufacturers' phones or even different models of phones from a single manufacturer.
There are two main types of charges for vehicles:
- To recharge a fuel vehicle's starter battery, where a modular charger is used.
- To recharge an electric vehicle (EV) battery pack.
Prolonging battery life: Memory effect (see below) should be prevented by fully discharging the battery once a month (once every 30 charges). This extends the life of the battery since memory effect is prevented while avoiding full charge cycles which are known to be hard on all types of dry-cell batteries, eventually resulting in a permanent decrease in battery capacity.
Memory effect, also known as lazy battery effect or battery memory, is an effect observed in nickel cadmium rechargeable batteries that causes them to hold less charge. It describes one very specific situation in which certain NiCd batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged. The battery appears to "remember" the smaller capacity. The source of the effect are changes of the characteristics of the underused active materials of the cell. The term is commonly misapplied to almost any case in which a battery appears to hold less charge than was expected. These cases are more likely due to battery age and use, leading to irreversible changes in the cells due to internal short-circuits, loss of electrolyte, or reversal of cells.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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