10-04-2017, 08:12 PM
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This article is presented by:
[u][b]YUSUF KIRMANI
STUDY OF QUALITY EQUIPMENTS
BATTERY CHARGER[/b][/u]
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.
BATTERY CHARGER IN DETAIL-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 from the current for a mobile phone battery.
Types of battery chargers
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.
Trickle
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.
Timer-based
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.
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 across 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 V, or "delta-V," charger, indicating that they monitor the voltage change.
A typical intelligent charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity.
Fast
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.
Pulse
Some chargers use pulse technology in which a pulse is fed to the battery. This DC pulse has a strictly controlled rise time, shape, 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.
Several kinds of pulse charging are patented.
Some chargers use pulses to check the current battery state when the charger is first connected, then use constant current charging during fast charging, then use pulse charging as a kind of trickle charging to maintain the charge.
Some chargers use "negative pulse charging", also called "reflex charging" or "burp charging" . Such chargers use both positive and brief negative current pulses. Such chargers don't work any better than pulse chargers that only use positive pulses.
Inductive
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 is no risk of electrocution.
Charge rate
This is often denoted as C and signifies a charge or discharge rate equal to the capacity of a battery divided by 1 hour. For example C for a 1600 mAh battery would be 1600 mA (or 1.6 amps). 2C is twice this rate and 1/2C is half the rate.
Applications
Since a battery charger is intended to be connected to a battery, it may not have voltage regulation or filtering of the DC voltage output. Battery chargers equipped with both voltage regulation and filtering may be identified as battery eliminator
Prolonging battery life
Many rumors circulate about the best practices to prolong battery life. What practices are best depend on the type of battery. It is rumored that Nickel-based cells, such as NiMH and NiCd, need to be fully discharged before each charge, or else the battery loses capacity over time in a phenomenon known as memory effect. However, this is only partially accurate: nickel alloy cells can be charged at any point throughout their discharge cycle--they do not have to be fully discharged. Memory effect should instead 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.