Modern, high capacity NiMH rechargeable batteries

A nickel metal hydride (or NiMH) battery is a type of rechargeable battery similar to a nickel-cadmium (NiCad) battery but which does not contain expensive (and environmentally risky) cadmium. This is why they are sometimes called the most environmentally friendly battery type. NiMH batteries tend to have a higher capacity than NiCads and suffer far less from voltage depression. However, when compared with lithium ion batteries they have a lower energy density and a higher self-discharge rate. They are used in hybrid vehicles such as the Toyota Prius, and electric vehicle development is underway. NiMH batteries perform better with high drain electronic devices like digital cameras and other common electronic devices, while for high torque power tools and other devices that require fast discharge rates, NiCd can outperform NiMH. Download high resolution version (600x800, 70 KB)nickel metal hydride batteries This is a copyrighted and/or trademarked logo. ... Download high resolution version (600x800, 70 KB)nickel metal hydride batteries This is a copyrighted and/or trademarked logo. ... Four double-A (AA) rechargable batteries In science and technology, a battery is a device that stores energy and makes it available in an electrical form. ... Rechargeable batteries are batteries that can be restored to full charge by the application of electrical energy. ... The nickel-cadmium battery (commonly abbreviated NiCd or NiCad) is a popular type of rechargeable battery for portable electronics and toys using the metals nickel and cadmium as the active chemicals. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Atomic mass 112. ... The phrase environmentally friendly is used to refer to goods or services considered to inflict little harm on the environment. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... With batteries, the memory effect, also known as lazy battery effect, is an effect observed in some rechargeable batteries that causes them to hold less charge. ... Lithium ion batteries (sometimes abbreviated Li-Ion) are a type of rechargeable battery commonly used in consumer electronics. ... Honda Insight, a hybrid gas-electric vehicle 2004 Toyota Prius, a hybrid gas-electric vehicle A hybrid vehicle uses multiple propulsion systems to provide motive power. ... Toyota redirects here. ... Prius may refer to: Hitachi Flora Prius, a personal computer. ... An electric vehicle is a vehicle whose motion is provided by electric motors. ...

Charging

When fast-charging, it is advisable to charge the NiMH batteries with intelligent (microprocessor controlled) chargers to prevent over-charging with large currents, which could damage the battery. Modern NiMH batteries contain catalysts to immediately deal with gases developed as a result of over-charging without being harmed (2 H₂ + O₂ ---catalyst--> 2 H₂O). This however only works with over-charging currents of up to C/10 h (nominal capacity divided by 10 hours). As a result of this reaction, the batteries will heat up considerably, marking the end of the charging process. Some quick chargers (one hour or less) include fans to keep the batteries cool. Microprocessors, including an Intel 80486DX2 and an Intel 80386 A microprocessor (abbreviated as µP or uP) is a computer electronic component made from miniaturized transistors on a single semiconductor integrated circuit (IC) (aka microchip or just chip). ... Battery charger A battery charger is a device used to put energy into a cell or battery by forcing an electric current through that cell or battery. ... A catalyst (Greek: καταλύτης) is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction (see also catalysis). ... In electricity, current refers to electric current, which is the flow of electric charge. ... Household Electric Fan A fan has two purposes – to move air for creature comfort or for ventilation and to move air or gas from one location to another for industrial purposes. ...

Some equipment manufacturers consider that NiMH can be safely charged in simple fixed (low) current chargers with or without timers, and that permanent over-charging is permissible with currents up to C/10 h. In fact, this is what happens in cheap cordless phone base stations and the cheapest battery chargers. Although this may be safe, it may not be good for the health of the battery. According to the Panasonic NiMH charging Manual (link below), permanent trickle charging (small current overcharging) can cause battery deterioration and the trickle charge rate should be limited to between 0.033×C per hour and 0.05×C per hour for a maximum of 20 hours to avoid damaging the batteries. Panasonic is principal sponsor of the Toyota F1 team Panasonic was also the name of a road bicycle racing team and a Finnish electronic music duo. ...

Long term maintenance charge of NiMH batteries needs to be by low duty cycle pulses of high current rather than continuous low current in order to preserve battery health.

Brand new batteries, or batteries which have been unused for some time, need "reforming" to reach their full capacity. For this reason new batteries may need several charge/discharge cycles before they operate to their advertised capacity.

Discharging

Care must also be taken during discharge to ensure that a cell in a series battery (for example the common arrangement of four AA cells in series in a digital camera) does not become totally flat and then reverse charged. This reverse charge can cause irreparable damage to the cell. Usually the device (e.g. camera) detects the safe end of discharge voltage of the series cells and shuts itself down, thus saving the cells from damage. An AA battery is 50. ... Reverse Charging is when a rechargeable battery is recharged with its polarity (plus/minus) reversed. ...

A single cell driving a load generally cannot become reverse charged, simply discharging down to 0 volts. This does not cause irreparable damage, and in fact if performed periodically and followed by a full recharge will help to maintain the cell's capacity and performance.

Nickel metal hydride batteries have a high self-discharge rate of approximately 30% per month and more. This is higher than that of NiCd batteries, which is around 20% per month. The self-discharge rate is highest for full batteries and drops off somewhat for lower charges. The rate is strongly affected by the temperature at which the batteries are stored. Recommended long time storage charge is around 40%.

Other Information

Common penlight-size (AA) batteries have nominal capacities C ranging from 1100 mA·h (3960 C) to 2700 mA·h (9720 C) at 1.2 V; the true useful capacities can be significantly lower and depend on the discharge rate. NiMH batteries have an alkaline electrolyte. The specific energy density for NiMH material is approximately 60 W·h/kg (220 kJ/kg), with a volumetric energy density of about 100 W·h/L (360 MJ/m³). The coulomb (symbol: C) is the SI unit of electric charge. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... An electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. ... This article is in need of attention from an expert on the subject. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The litre (or liter in US) is a metric unit of volume. ...

Chemistry

The "metal" in a NiMH battery is actually an intermetallic compound. Many different compounds have been developed for this application, but those in current use fall into two classes. The most common is AB₅, where A is a rare earth mixture and/or titanium and B is nickel, cobalt, manganese, and/or aluminum. Higher-capacity "multi-component" electrodes are based on AB₂ compounds, where A is titanium and/or vanadium and B is zirconium or nickel, modified with chromium, cobalt, iron, and/or manganese [1]. Intermetallics is concerned with all aspects of ordered chemical compounds between two or more metals and notably with their applications. ... A rare earth is an oxide of a rare earth element. ... General Name, Symbol, Number titanium, Ti, 22 Chemical series transition metals Group, Period, Block 4, 4, d Appearance silvery metallic Atomic mass 47. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... This article is on the chemical element. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Atomic mass 54. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Vanadium is a chemical element in the periodic table that has the symbol V and atomic number 23. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Atomic mass 91. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...

Any of these compounds serves the same role, reversibly forming a mixture of metal hydride compounds. When hydrogen ions are forced out of the potassium hydroxide electrolyte solution by the voltage applied during charging, this process prevents them from forming a gas, allowing a low pressure and volume to be maintained. As the battery is discharged, these same ions are released to participate in the reverse reaction. The chemical compound potassium hydroxide, (KOH) sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. ...

External links

• Panasonic NiMH charging manual (PDF)
• "The Nickel-based Battery" at BatteryUniversity.com
• NiMH Batteries, Memory and Thermal Runaway
• Battery Care & Tips
• NiMH Battery Handbook
• Steve's Digicams - Rechargeable Battery Information
• NiMH Batteries and Chargers - Knowledge Base
• R/C Battery Clinic
• Batteries in a Portable World
• How to charge Nickel Metal Hydride Batteries.
• Battery Chargers and Charging Methods