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How a Battery Charger Works

written by: Swagatam • edited by: Lamar Stonecypher • updated: 4/5/2010

Chargeable batteries are produced and used extensively today for different applications. But without a battery charger these batteries can become quite worthless. Learn how a battery charger works in this article.

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    Whether its your mobile phone, emergency light or the vehicle you own, the extensive use of batteries is evident everywhere. Chargeable batteries are also widely used in inverters, where its DC voltage is converted into mains AC voltage and is used to power the household appliances during mains power failure.

    The importance of a battery lies in the fact that it’s electricity that you can carry. Moreover when the power in a battery gets exhausted, it can be refilled and topped up or charged (obviously this is true only with the chargeable ones) making it a very efficient and an economical power house.

    A battery charger circuit may be quite simple in design but generally batteries don’t like crude charging voltages and therefore it is always recommended the use of good quality, constant voltage type of chargers to keep the battery in a good shape and consistent.

    Before learning how to use a battery charger, it will be important first to know its working principle.

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    How does a Battery Charger Work?

    The answer to the question “how does a battery charger work" may be easily understood through the following points:

    • A battery charger is basically a DC power supply source. Here a transformer is used to step down the AC mains input voltage to the required level as per the rating of the transformer.

    • This transformer is always a high power type and is able to produce a high current output as required by most lead-acid batteries.

    • A bridge rectifier configuration is used to rectify the low voltage AC into DC and is further smoothed by a high value electrolytic capacitor.

    • This DC is fed to an electronic circuit which regulates the voltage into a constant level and is applied to the battery under charge, where the energy is stored through an internal process of chemical reaction.

    • In automatic battery chargers a voltage sensor circuit is incorporated to sense the voltage of the battery under charge. The charger is automatically switched OFF when the battery voltage reaches the required optimum level.
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    How to Calculate the Charging or Discharging time of a Battery

    • The rated current capacity of a chargeable battery may vary according to its applications. Its current holding capacity is expressed in ampere-hour (AH). This unit of measurement may be defined as the maximum current through which the particular battery can be fully charged or discharged in one hour.

    • If for example a 4 AH fully charged battery is discharged at 4 ampere rate, then ideally it should take an hour for it to get fully discharged (but practically it can be seen that the back up time is much less than an hour due to the existing inefficiency in all batteries).

    • Similarly if the same battery is charged at 4 ampere rate, then it should take an hour to get it fully charged. But it’s never a good practice to charge or discharge batteries at their full current ratings.

    • Ideally the charging and the discharging process should be carried out gradually for about 10 hours. So to find out the optimum charging current of a battery, just divide its AH by 10, the same is true to find its correct continuous discharge rate.Lead Acid Battery, image 
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    How to Use a Battery Charger?

    Now let’s study exactly how to use a battery charger through the following brief explanation:A Typical Battery Charger, Image 

    • A general type of battery charger will consist of two output terminals marked red and black.

    • It should also consist of an ammeter to display the charging current and a voltage selector switch.

    • Begin by selecting the appropriate charging voltage as per the battery used.

    • Taking due care of the polarity, you may just connect the red terminal to the positive and the black to the negative of the battery under charge.

    • The ammeter will instantly indicate the charging current. The battery will now gradually get charged, the ammeter reading will go down proportionately.

    • Once it reaches the zero mark, will mean that the battery is full and may be disconnected from the charger.

    If you have any further doubt regarding how does a battery charger work or how to use to it, feel free to add your comments (comments need moderation and may take time to appear).

    Battery Image Credit:

    Battery Charger Image Credit: