All battery chargers have one thing in common: they work by feeding an electric current through batteries for a period of time. A good battery charger provides the base for batteries that are durable and perform well. In a price-sensitive market, chargers often receive low priority and get the “after-thought” status. Battery and charger must go together like a horse and carriage.
Charging/Discharging of Batteries
Charging a battery essentially involves reversing the chemical reactions that take place when it discharges. In a laptop battery, for example, charging and discharging involve shunting lithium ions (atoms missing electrons) back and forth, from one electrode (where there are many of them) to another electrode (where there are few). Since the ions all carry a positive charge, it’s easier to move them to the “empty” electrode at the start. As they start to build up there, it gets harder to pack more of them in, making the later stages of charging harder work than the earlier ones. Thus discharging of battery gives out energy, charging takes energy in and stores it by resetting the battery chemicals to how they were originally.
The Three Stages of Charging
There are three different stages that your battery will go through when you use the right deep cycle battery charger, and understanding these stages show the importance of knowing what is a deep cycle battery charger
- Bulk: During the bulk charge stage, the maximum current will be sent directly to the battery at a constant voltage.
- Absorption: At this point, the internal resistance of the battery is going to increase as it charges, which will slowly decrease the voltage put out by the charger in order to get the battery to its fullest state.
- Float: During this process, the battery will begin to “float” which is essentially when the battery is encouraged not to discharge. However, this process isn’t going to last forever, and you will be required to top up the battery at least once a month to maintain the floating cycle.
Working of a Battery Charger
Batteries convert chemical energy into electrical energy. Chargers do the opposite: push electrons into the electrolyte to restore the chemical energy. Different electrolytes store energy in different ways, due to differences in chemical processes, electode geometry/composition, etc. so the charger must drive a current and voltage to match the specific battery type.
- For example, Lithium-Ion chargers works on Constant Current Constant Voltage (CCCV).They first push a constant current until the cell reaches a topping voltage. The charger then keeps a constant voltage, and lets the current freely glide down until a certain “end of charge” threshold is reached. Optionally, the charger may continue shooting short current pulses to compensate for self-discharge.
- Nickel-type chargers (typical Ni-Cd, NiMH batteries) keep a Constant Current for as long as the voltage is rising and/or the temperature does not rise (charge takes heat from ambient so the cell is cool during charging). A charged Ni-Cd cell will show a slight drop in voltage, while a Ni-MH will stay constant, with temperature rising in both cases. Smart chargers track the temperature and voltage gradients, to stop the charge without overheating the cell.
- Lead-Acid chargers (Cars, motor boats, etc.) are similar to Lithium-Ion types: there’s a bulk charge stage at constant current that takes roughly 3/4 of the charging time, followed by a topping charge stage where the voltage remains constant and the current drops exponentially, and a floating charge that basically prevents self-discharge.
Selection of Battery Chargers
The best chargers work intelligently, using microchip-based electronic circuits to sense how much charge is stored in the batteries, figuring out from such things as changes in the battery voltage (technically called delta V or ΔV) and cell temperature (delta T or ΔT) when the charging is likely to be “done,” and then switching off the current or changing to a low trickle charge at the appropriate time; in theory, it’s impossible to overcharge with an intelligent charger.
The first rule of battery charging is that a charger designed for one kind of battery may not be suitable for charging another: you can’t charge a cellphone with a car battery charger, but neither should you charge NiMH batteries with a Nickel Cadmium charger. It’s important that you buy batteries that suit the charger you have or replace your charger accordingly. Note the voltage and current that the batteries require (it will be marked on the battery package or on the batteries themselves), be sure to choose a charger with the right voltage and current to go with them, and charge for the correct amount of time.
Battery charger for vehicles There are two main types of chargers used for vehicles:
- To recharge a fuel vehicle’s starter’s battery, where a modular charger is used; typically an 3-stage charger
- To recharge an electric vehicle (EV) battery pack
- An average car battery has a capacity of around 48 Amp hours which means that, fully charged, it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours and so on.
- A basic charger usually charges at around 2 amps – and so needs 24 hours to deliver the 48 amps needed to fully charge a flat, 48 Amp hour battery.
- But there is a wide range of chargers with different charge rates on the market – from 2 to 10 amps. The higher the charge output, the faster a flat battery is recharged. Fast charging, however, is undesirable as it can buckle the battery plates.
- A basic home battery charger incorporates a transformer and rectifier, to change the mains 110/220 volt alternating current to 12 volt direct current , and allows the mains supply to provide a charging current at a rate determined by the state of the battery. In the case of a battery in good condition, the rate of charge may be around 3 to 6 amps with a normal home charger.