Traction battery charger

How does a battery charger work? Different types of battery chargers

How does a battery charger work? Different types of battery chargers

All chargers draw Alternating Current (AC) grid power and convert to Direct Current. In the process, there will be some AC ripples which need to be kept to less than 3%. Some of the battery chargers in the market have features to filter the ripples, which would otherwise harm the battery during charging. In any case, it is better to use 3 phase supply since single-phase current has 10 % ripple.
Constant voltage allows the full current of the battery charger to flow into the battery until the power supply reaches its preset voltage. The current will then taper down to a minimum value once that voltage level is reached.  The battery can be left connected to the battery charger until ready for use and will remain at that “float voltage”, trickle charging to compensate for normal battery self-discharge.
A constant current is a simple form of charging batteries, with the current level set at approximately 10% of the maximum battery rating. Charge times are relatively long with the disadvantage that the battery may overheat if it is overcharged, leading to premature battery failures &  replacement.  This method is suitable for Nickel Metal hydride (Ni-MH) type of batteries.  The battery must be disconnected, or a timer function used once charged.
Constant voltage / constant current (CVCC) is a combination of the above two methods. The charger limits the amount of current to a pre-set level until the battery reaches a preset voltage level. The current then reduces as the battery becomes fully charged. The lead-acid battery uses the constant current constant voltage (CC/CV) charge method. A regulated current raises the terminal voltage until the upper charge voltage limit is reached, at which point the current drops due to saturation.

Different types of battery chargers
Existing battery charging technology relies on microprocessors (computer chips) to recharge, using 3 steps of regulated charging. These are the “smart chargers”. These are readily available. The three steps in lead-acid battery charging are the main current inputs for conversion, and float charge on a continuous period. Periodic equalisation to maintain uniformity is necessary. Use battery manufacturer’s recommendations on charging procedures and voltages or a quality microprocessor controlled charger to maintain battery capacity and service life.
The “smart chargers” are profiled with contemporary charging technology in mind, and also take information from the battery to provide maximum charge benefit with minimum observation.

VRLA – Gel and AGM batteries require different voltage settings. This is to avoid gassing and dry-out. The oxygen recombination process in a Valve Regulated Lead-acid (VRLA) battery requires a lower voltage setting to avoid hydrogen evolution and cell dry-out.
The maximum charging voltage for Gel batteries is 14.1 or 14.4 volts, which is lower than a wet or AGM VRLA type battery needs for a full charge. Exceeding this voltage in a Gel battery can cause bubbles in the electrolyte gel and permanent damage.
The current rating for chargers recommend sizing the charger at a maximum current of 25% of the battery capacity. Some batteries specify 10% of capacity It is safer to use a lower current, although it takes longer.
A constant current -constant voltage (CCCV) charge method is a good option. A constant current increases the terminal voltage until the upper charge voltage limit is reached, at which point the current drops due to saturation. The charge time is 12–16 hours and longer (36 hours) for large stationary batteries. The lead-acid battery is slower and cannot be charged as quickly as other battery systems. With the CCCV method, lead-acid batteries are charged in three steps, [1] constant-current charge, [2] Constant voltage and [3] float charge on completion of charge. The constant-current charge applies the bulk of the charge and takes up roughly half of the required charge time; the topping charge continues at a lower charge current and provides saturation, and the continuous float charge compensates for the loss caused by self-discharge. During the constant-current charge, the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with Constant Voltage that lasts another 7–10 hours. The float charge in the third step maintains the battery at full charge.

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