A battery charger, or recharger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.
The charging protocol depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging and can be recharged by connection to a constant voltage source or a constant current source; simple chargers of this type require manual disconnection at the end of the charge cycle, or may have a timer to cut off charging current at a fixed time. Other battery types cannot withstand long high-rate over-charging; the charger may have temperature or voltage sensing circuits and a microprocessor controller to adjust the charging current, determine the state of charge, and cut off at the end of charge.
A trickle charger provides a relatively small amount of current, only enough to counteract self-discharge of a battery that is idle for a long time. Slow battery chargers may take several hours to complete a charge; high-rate chargers may restore most capacity within minutes or less than an hour, but generally require monitoring of the battery to protect it from overcharge. Electric vehicles need high-rate chargers for public access; installation of such chargers and the distribution support for them is an issue in the proposed adoption of electric cars.
Charge rate is often denoted as C or C-rate and signifies a charge or discharge rate equal to the capacity of a battery in one hour.
A battery charger may be specified in terms of the battery capacity or C rate; a charger rated C/10 would return the battery capacity in 10 hours, a charger rated at 4C would charge the battery in 15 minutes. Very rapid charging rates, 1 hour or less, generally require the charger to carefully monitor battery parameters such as terminal voltage and temperature to prevent overcharging and damage to the cells.
Types of battery chargers
A simple charger works by supplying a constant DC or pulsed DC power source to a 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 trade off 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. These chargers can supply either a constant voltage or a constant current to the battery.
Simple AC-powered battery chargers have much higher ripple current and ripple voltage than other kinds of battery supplies. When the ripple current is within the battery-manufacturer-recommended level, the ripple voltage will also be well within the recommended level. The maximum ripple current for a typical 12 V 100 Ah VRLA battery is 5 amps. As long as the ripple current is not excessive (more than 3 to 4 times the battery-manufacturer-recommended level), the expected life of a ripple-charged VRLA battery is within 3% of the life of a constant DC-charged battery.
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 standard overnight chargers if used with standard NiMH cells that do not have the special control circuitry.
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 toothbrushesand other devices used in bathrooms. Because there are no open electrical contacts, there is no risk of electrocution.
|A “smart charger” should not be confused with a “smart battery”. A smart battery is generally defined as one containing some sort of electronic device or “chip” that can communicate with a smart charger about battery characteristics and condition. A smart battery generally requires a smart charger it can communicate with (see Smart Battery Data). A smart charger is defined as a charger that can respond to the condition of a battery, and modify its charging actions accordingly.|
Example of a smart charger for AA and AAA batteries
Some smart chargers are designed to charge:
- “smart” batteries.
- “dumb” batteries, which lack any internal electronic circuitry.
The term “smart battery charger” is thoroughly ambiguous, since it is not clear whether the adjective “smart” refers to the battery or only to the charger.
The output current of a smart charger depends upon the battery’s state. An intelligent charger may monitor the battery’s voltage, temperature or time under charge to determine the optimum charge current and to terminate charging.
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 ΔV, “delta-V,” or sometimes “delta peak”, charger, indicating that they monitor the voltage change.
The problem is, the magnitude of “delta-V” can become very small or even non-existent if (very) high capacity rechargeable batteries are recharged. This can cause even an intelligent battery charger to not sense that the batteries are actually already fully charged, and continue charging. Overcharging of the batteries will result in some cases. However, many so called intelligent chargers employ a combination of cut off systems, which should prevent overcharging in the vast majority of cases.
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.
Solar chargers convert light energy into DC current. They are generally portable, but can also be fixed mount. Fixed mount solar chargers are also known as solar panels. Solar panels are often connected to the electrical grid, whereas portable solar chargers are used off-the-grid (i.e. cars, boats, or RVs).
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.
A trickle charger is typically a low-current (5–1,500 mA) battery charger. A trickle charger is generally used to charge small capacity batteries (2–30 Ah). These types of battery chargers are also used to maintain larger capacity batteries (> 30 Ah) that are typically found on cars, boats, RVs and other related vehicles. In larger applications, the current of the battery charger is sufficient only to provide a maintenance or trickle current (trickle is commonly the last charging stage of most battery chargers). Depending on the technology of the trickle charger, it can be left connected to the battery indefinitely. Some battery chargers that can be left connected to the battery without causing the battery damage are also referred to as smart or intelligent chargers.
Universal battery charger–analyzers
The most sophisticated types are used in critical applications (e.g. military or aviation batteries). These heavy-duty automatic “intelligent charging” systems can be programmed with complex charging cycles specified by the battery maker. The best are universal (i.e. can charge all battery types), and include automatic capacity testing and analyzing functions too.
A powerbank is a portable device that can supply USB power using stored energy in its built-in batteries. Powerbanks usually recharge with USB power.
- mAh: amount of mA × time at 5V ideally. Many manufacturers measure this at the voltage of battery inside, hence they show more than actual.
- Simultaneous charging and discharging: need to specify if the powerbank can be used while it is charging.
- Number of output ports: This specifies the number of devices that can be charged simultaneously.
- Output current rating: This specifies the current rating that it can charge maximum. The higher the number, better the powerbank. This can vary from output port to output port.
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 eliminators.
Battery charger for vehicles
There are two main types of charges for vehicles:
- To recharge a fuel vehicle’s starter battery, where a modular charger is used
- To recharge an electric vehicle (EV) battery pack
Chargers rated only one or two amperes may be used to maintain charge on parked vehicle batteries or for small batteries on garden tractors or similar equipment. A motorist may keep a charger rated a few amperes to ten or fifteen amperes for maintenance of automobile batteries or to recharge a vehicle battery that has accidentally discharged. Service stations and commercial garages will have a large charger to fully charge a battery in an hour or two; often these chargers can briefly source the hundreds of amperes required to crank an internal combustion engine starter.
Mobile phone charger
Micro USB mobile phone charger
Most mobile phone chargers are not really chargers, only power adapters that provide a power source for the charging circuitry which is almost always contained within the mobile phone.Older ones are notoriously diverse, having a wide variety of DC connector-styles and voltages, most of which are not compatible with other manufacturers’ phones or even different models of phones from a single manufacturer.
Users of publicly accessible charging kiosks must be able to cross-reference connectors with device brands/models and individual charge parameters and thus ensure delivery of the correct charge for their mobile device. A database-driven system is one solution, and is being incorporated into some designs of charging kiosks.
Mobile phones can usually accept a relatively wide range of voltages, as long as it is sufficiently above the phone battery’s voltage. However, if the voltage is too high, it can damage the phone. Mostly, the voltage is 5 volts or slightly higher, but it can sometimes vary up to 12 volts when the power source is not loaded.
There are also human-powered chargers sold on the market, which typically consists of a dynamo powered by a hand crank and extension cords. A French startup offers a kind of dynamo charger inspired by the ratchet that can be used with only one hand.There are also solar chargers, including one that is a fully mobile personal charger and panel, which you can easily transport.
Stationary battery plants
Telecommunications, electric power, and computer uninterrupted power supply facilities may have very large standby battery banks (installed in battery rooms) to maintain critical loads for several hours during interruptions of primary grid power. Such chargers are permanently installed and equipped with temperature compensation, supervisory alarms for various system faults, and often redundant independent power supplies and redundant rectifier systems. Chargers for stationary battery plants may have adequate voltage regulation and filtration and sufficient current capacity to allow the battery to be disconnected for maintenance, while the charger supplies the DC system load. Capacity of the charger is specified to maintain the system load and recharge a completely discharged battery within, say, 8 hours or other interval.