Battery charger

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This charger charges the battery until it reaches a specific voltage and then it trickle charges the battery until it is removed.

A simple charger equivalent to a AC-DC wall adapter. It applies 300mA to the battery at all times, which damages the battery if left connected too long.

A battery charger is a device used to put energy into a cell or (rechargeable) battery by forcing an electric current through it.

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 to the current for a mobile phone battery.

1 Types of battery chargers
2 "Short circuiting"
3 Mobile phone charger
4 References

[edit] Types of battery chargers

[edit] Simple

A simple charger works by connecting a constant DC power source to the 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.

[edit] Timer-based

The output of a timer charger is terminated after a pre-determined time. Timer chargers were the most common type for Ni-Cd cells in the late 1990s for example.

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.

[edit] Intelligent

Output current depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature and/or time under charge to determine the optimum charge current at that instant. Charging is terminated when a combination of the voltage, temperature and/or time indicates that the battery is fully charged.

For Ni-Cd and NiMH batteries, the voltage over the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV charger, indicating that they monitor the voltage change.

[edit] Fast

Fast chargers, made by VARTA^[1] and other companies, 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.

[edit] USB-based

Since the Universal Serial Bus specification provides for a five-volt power supply, it's possible to use a USB receptable as a power source for recharging batteries. Products based on this approach include chargers designed to charge standard NiMH cells^[2], and custom NiMH batteries with built-in USB plugs and circuitry which eliminate the need for a separate charger.^[3]

[edit] "Short circuiting"

A short circuit (connecting the output terminals together) does not usually damage a simple battery charger. For that reason it is a suitable source of DC voltage for experimentation. It may, however, require an external capacitor to be connected across its output terminals in order to "smooth" the voltage sufficiently, which may be thought of as a DC voltage plus a "ripple" voltage added to it. To see the difference between connecting and not connecting a capacitor, connect also an oscilloscope across the output terminals. Note that there may be an internal resistance connected to limit the short circuit current, and the value of that internal resistance may have to be taken into consideration in experiments.

Pay-per-charge kiosk, illustrating the variety of mobile phone charger connectors.

[edit] Mobile phone charger

Battery chargers for mobile phones and other devices are notable in that they come in a wide variety of connector-styles and voltages, most of which are not compatible with other manufactuers' phones or even different models of phones from a single manufacturer. In many cases, although a connector may be the same for devices from the same brand or compatible with a device from another brand, the actual charging parameters may differ – using a charger just because it has the "right" connector may result in an inadequate charge or even permanently damage the device.^[4]

Users of publicly accessible charging kiosks must be able to cross-reference connectors with device brands/models and individual charge parameters and thus ensure delivery of the correct charge for their mobile device. A database-driven system is one solution, and is being incorporated into some of the latest designs of charging kiosks.

There are also human-powered chargers sold on the market, which typically consists of a dynamo powered by a hand crank and extension cords. ^[5] There are also solar chargers.^[6]

China is making a national standard on mobile phone chargers using USB port.^[7]