Car battery charger

Monday, 22 January 2007

Owing to the prosperity of mobile communication and digital entertainment, the percentage of people possessing mobile phones, personal digital assistants (PDA), MP3 players, camcorders, digital cameras, and laptop computers has been rapidly increased. Many of these devices include rechargeable batteries that enable the user to prolong the life of the item without having to purchase new batteries. In particular, cellular phone use has grown tremendously in a short period of time. The cellular phone has a significant usage outside of the home or business where traditional landline telephones still predominate. As a result, a significant percentage of cell phones are used in and around automobiles and other vehicles. Consistent use or even extended non-use of the cellular telephone naturally drains the cell phone battery. To convince people to utilize the mobile business system, the most important thing except the quality of the communication signal is the working time of the battery providing power. Although the battery manufacturers continually work on the invention of a long-term battery, the working time of a battery is always limited. A battery needs to be recharged. To provide high mobility and continuous utilization of the device, in a mobile telephone, for example, the batteries have a high capacity and must be reenergized in the shortest time by network power or by the on-board power of a vehicle. Rechargeable batteries, such as nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, lithium ion batteries, lithium polymer batteries, and lithium-metal secondary batteries, are an important source of portable power for transportation and recreation equipment, utility devices, and other electrical applications. Maintenance of a rechargeable battery, also referred to as a storage or secondary battery, often requires charging the battery by converting power available from an alternating current (AC) source to meet the needs of the battery. Most high performance portable electronic devices rely on rechargeable battery packs to supply the power required for portable operation. The rechargeable battery pack typically includes two or more electrochemical cells disposed within a housing. The housing includes a latching apparatus that allows the rechargeable battery to be detachably coupled to the portable electronic device.

Portable battery operated devices have benefited from remarkable improvements in battery life and battery charging facilities. There are several techniques by which this recharging may be accomplished. Two of the most common include conventional outlet chargers and car battery chargers. The outlet charger plugs into a conventional wall outlet and translates the AC voltage to a DC voltage and maximum current level suitable for the battery being recharged. Although portable battery operated electronic devices are normally used near electrical outlets providing unlimited power supply, in many applications, the portable battery operated device is used for extended periods of time in an open outdoor and/or mobile application environment, where there is no readily available unlimited power source such as a wall outlet. Some electronic devices, such as notebook computers and cell phones, are frequently used outdoors, and therefore, there is a need to permit charging of the battery packs using the power sources installed in vehicles (such as cars, trucks, boats, etc.). In these mobile applications, there may only be available a vehicular battery power supply or other such mobile battery power supply as the only source for recharging a portable device's rechargeable battery. Similarly, the car battery chargers typically plug into a cigarette lighter and convert the 12 V DC car battery voltage to a voltage of 5 V DC and current level suitable for the battery being charged. To recharge the batteries, a battery operated devices may include a charging circuit, which controls charging of the battery through the communication device when the battery operated electronic devices is connected to an external power supply. For example, the battery operated electronic devices may be connected to a vehicle electrical system through a cigarette lighter or to a conventional main power supply through a wall outlet. A transformer is employed to convert the wall outlet power supply to a standard DC voltage. Alternatively, the battery may be detached from the battery operated electronic devices and inserted into a charger that provides the necessary power regulation for charging the battery. Adapters, such as hands-free adapters, mobile transceiver adapters, cigarette lighter adapters, or wall charger adapters, can be connected to a vehicle cigarette lighter or an electrical outlet to provide an external power source for charging a battery attached to the portable electronic device. Many of these portable electronic devices use internal battery chargers to decrease the size of the adapters and increase convenience to the user.

Portable electronic devices, such as cell phones, may be placed on car dashboards and powered, either directly or indirectly, via the vehicle cigarette lighter. A typical car battery charger has one end that is inserted into a power supply, and another end that has an extendable cord connected to the cellular phone battery. Most car battery chargers include a fixed frame and a power signaling cable. The power signaling cable has two ends. One end contains the power plug and the other end contains a signaling plug. The signaling plug is connected to a mobile phone or a PDA while the power plug is plugged into a cigarette lighter socket inside an automobile. The adapter of a cellular phone has a signal jack for receiving the plug of a hand-free speaker and microphone circuit assembly, a power jack for receiving the first plug of a cable, which has a second plug for connection to the socket for cigarette lighter of a motor vehicle to obtain car battery power supply from it, and an electric connector for connection to a cellular phone. During charging the cell phone remains fully functional for the user to make outgoing calls or to receive incoming calls. The power signaling cable of existing chargers is long enough so that an individual can talk on the telephone while it is charging, but the charging cord is also long enough so that it can slide to different areas of the vehicle passenger compartment and not be accessible to the driver, or other vehicle occupants who seek to make or answer a call. The recharging of depleted batteries involves use of the primary battery which provides the energy source to start the car. It is critically important that the charging of the secondary batteries from the main battery be in a controlled manner that both provides an adequate charge to the secondary batteries and does not deplete the primary battery so that it can no longer perform vital function of starting the vehicle's engine. A battery charger using a car battery as a power source is provided with a computer-controlled anti-overdischarge device which stops charging the battery when the voltage of the car battery, falls below a lower limit value. This anti-overdischarge device is necessary to preserve a minimum capacity of the car battery for starting the car engine.

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