Battery charger: Difference between revisions
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== See also == |
== See also == |
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* [http://www.iranBattery.ir Battery is our business] |
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==References== |
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Revision as of 13:49, 15 January 2011
A battery charger is a device used to put energy into a secondary 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 supplying a constant or DC 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 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. These chargers can supply either a constant voltage or a constant current to the battery.
Trickle
A trickle charger, also known as a battery trickle charger, is typically a low-current (500–1,500 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. Utilizing the battery charger in this fashion is how these battery chargers got their name. 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. Battery chargers that can be left connected to the battery without causing the battery damage are also referred to as smart or intelligent chargers.
Timer-based
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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 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[quantify] capacity rechargeable batteries are recharged.[citation needed] 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.[1]
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 standard overnight chargers 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, 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.[2] With pulse charging, high instantaneous voltages can be applied without overheating the battery. In a Lead–acid battery, this breaks down lead-sulfate crystals, thus greatly extending the battery service life.[3]
Several kinds of pulse charging are patented.[4][5][6] Others are open source hardware.[7]
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.[8]
Some chargers use "negative pulse charging", also called "reflex charging" or "burp charging".[9] Such chargers use both positive and brief negative current pulses. There is no significant evidence, however, that negative pulse charging is more effective than ordinary pulse charging.[10][11]
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 are no open electrical contacts, there is no risk of electrocution.
USB-based
Since the Universal Serial Bus specification provides for a five-volt power supply, it is possible to use a USB cable as a power source for recharging batteries. Products based on this approach include chargers for cellular phones and portable digital audio players. They may be fully compliant USB peripheral devices adhering to USB power discipline, or uncontrolled in the manner of USB decorations.
Solar chargers
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, where as portable solar chargers as used off-the-grid (i.e. cars, boats, or RVs).
Although portable solar chargers obtain energy from the sun only, they still can (depending on the technology) be used in low light (i.e. cloudy) applications. Portable solar charger are typically used for trickle charging, although some solar charger (depending on the wattage), can completely recharge batteries. Although Portable wind turbines are also sold. Some, including the Kinesis K3, can work either way.
Charge rate
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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.[12] For a 1.6Ah battery, C = 1.6A. A charge rate of C/2 = 0.8A would need two hours, and a charge rate of 2C = 3.2A would need 30 minutes to fully charge the battery from an empty state, if supported by the battery. This also assumes that the battery is 100% efficient at absorbing the charge.
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 eliminators.
Mobile phone charger
Most mobile phone chargers are not really chargers, only adapters that provide a power source for the charging circuitry which is almost always contained within the mobile phone.[13] They are notably 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 relatively wide range of voltages[citation needed], 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. There are also solar chargers.
China and other countries are making a national standard on mobile phone chargers using the USB standard.[14] Starting in 2010, SonyEricsson, Apple, Nokia, Motorola, Samsung and RIM will begin making handsets with a standard phone charger based on the micro-USB connector.[15] On October 22, 2009, the International Telecommunication Union announced a standard for a universal charger for mobile handsets (Micro-USB).[16]
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.
Battery electric vehicle
These vehicles include a battery pack, so generally use series charger.
A 10 Ampere-hour battery could take 15 hours to reach a fully charged state from a fully discharged condition with a 1 Ampere charger as it would require roughly 1.5 times the battery's capacity.
Public EV charging[17] heads (aka: stations) provide 6 kW (host power of 208 to 240 VAC off a 40 amp circuit). 6 kW will recharge an EV roughly 6 times faster than 1 kW overnight charging.
Rapid charging results in even faster recharge times and is limited only by available AC power and the type of charging system.[18]
On board EV chargers (change AC power to DC power to recharge the EV's pack) can be:
- Isolated: they make no physical connection between the A/C electrical mains and the batteries being charged. These typically employ some form of Inductive charging. Some isolated chargers may be used in parallel. This allows for an increased charge current and reduced charging times. The battery has a maximum current rating that cannot be exceeded
- Non-isolated: the battery charger has a direct electrical connection to the A/C outlet's wiring. Non-isolated chargers cannot be used in parallel.
Power Factor Correction (PFC) chargers can more closely approach the maximum current the plug can deliver, shortening charging time.
- Charge stations
There is a list of public EV charging stations in the U.S.A. and worldwide[17]
Project Better Place is deploying a network of charging stations and subsidizing vehicle battery costs through leases and credits.
- Non-contact magnetic charging
Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an electric transport system (called Online Electric Vehicle, OLEV) where the vehicles get their power needs from cables underneath the surface of the road via non-contact magnetic charging, (where a power source is placed underneath the road surface and power is wirelessly picked up on the vehicle itself. As a possible solution to traffic congestion and to improve overall efficiency by minimizing air resistance and so reduce energy consumption, the test vehicles followed the power track in a convoy formation[19]
Use in experiments
A battery charger can work as a DC power adapter for experimentation. It may, however, require an external capacitor to be connected across its output terminals in order to "smooth" the voltage sufficiently, which may be thought of as a DC voltage plus a "ripple" voltage added to it. Note that there may be an internal resistance connected to limit the short circuit current, and the value of that internal resistance may have to be taken into consideration in experiments.
Prolonging battery life
What practices are best depend on the type of battery. Nickel-based cells, such as NiMH and NiCd, need to be fully discharged occassionally, or else the battery loses capacity over time in a phenomenon known as "memory effect". Once a month (once every 30 charges) is sometimes recommended.[citation needed] 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.
Most modern cell phones, laptops, and most electric vehicles use Lithium-ion batteries. These batteries last longest if the battery is frequently charged; fully discharging them will degrade their capacity relatively quickly.[20] When storing however, lithium batteries degrade more while fully charged than if they are only 40% charged. Degradation also occurs faster at higher temperatures. Degradation in lithium-ion batteries is caused by an increased internal battery resistance due to cell oxidation. This decreases the efficiency of the battery, resulting in less net current available to be drawn from the battery. [citation needed]
Internal combustion engine vehicles, such as boats, RVs, ATVs, motorcycles, cars, trucks, and more use lead–acid batteries. These batteries employ a sulfuric acid electrolyte and can generally be charged and discharged without exhibiting memory effect, though sulfation (a chemical reaction in the battery which deposits a layer of sulfates on the lead) will occur over time. Keeping the electrolyte level in the recommended range is necessary. When discharged, these batteries should be recharged immediately in order to prevent sulfation. These sulfates are electrically insulating and therefore interfere with the transfer of charge from the sulfuric acid to the lead, resulting in a lower maximum current than can be drawn from the battery. Sulfated lead acid batteries typically need replacing.
Lead–acid batteries will experience substantially longer life when a maintenance charger is used to float the battery. This prevents the battery from ever being below 100% charge, preventing sulfate from forming. Proper temperature compensated float voltage should be used to achieve the best results.
See also
- Battery is our business
- Battery eliminator
- Battery holder
- Battery management system
- List of battery sizes
- Carport
- Charge controller
- Lithium-ion battery
- Recharging alkaline batteries
- Solar energy
- Solar lamp
- Underwriters Laboratories (UL) certification.
References
- ^ Dave Etchells. "The Great Battery Shootout".
- ^ "AN913: Switch-Mode, Linear, and Pulse Charging Techniques for Li+ Battery in Mobile Phones and PDAs". Maxim. 2001.
- ^ "Lead–acid battery sulfation". Archived from the original on 2007-04-02.
- ^ ""fast pulse battery charger" patent". 2003.
- ^ "Battery charger with current pulse regulation" patented 1981 United States Patent 4355275
- ^ "Pulse-charge battery charger" patented 1997 United States Patent 5633574
- ^ http://www.dallas.net/~jvpoll/Battery/aaPictures.html Pulse-charger/desulfator circuit schematic
- ^ "Pulse Maintenance charging."
- ^ "The pulse power(tm) battery charging system"
- ^ "Negative Pulse Charge, or "Burp" Charging: Fact or Fiction?"
- ^ Tech Brief: Negative Pulse Charging Myths and Facts and Negative Pulse Charging: Myths and Facts
- ^ [1] A Guide to Understanding Battery Specifications, MIT Electric Vehicle Team, December 2008
- ^ Mobile phone battery care
- ^ China to work out national standard for mobile phone chargers
- ^ PC World:Universal Chargers are a Good Start Jan 2009
- ^ Oct 22, 2009, ITU press release Universal charger for mobile phone handsets
- ^ a b EV Charger News - Home
- ^ Green Car Congress: Fuji Heavy Speeds Up Recharging of R1e EV
- ^ http://www.gizmag.com/kaist-olev-electric-vehicle/12557/
- ^ "How to prolong lithium-based batteries". September 2006. Retrieved November 21, 2009.
