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An induction cooker uses induction heating for cooking. A ferromagnetic or ferrimagnetic coated pot is placed above an induction coil for the heating process to take place. This type of hob (or, in American English stove top or cooktop) does not work with non-ferromagnetic cookware, such as glass, aluminum, and most stainless steel, nor with ferromagnetic material covered with a conductive layer, such as a copper-bottomed pan.

Induction cookers are faster and more energy-efficient than traditional hobs. Additionally, the risk of accidental burning is diminished since the hob itself only gets marginally hot (due to heat conduction down from cookware), allowing direct contact with a reduced chance of harm. Also, no heat is lost to the air directly from the hob, keeping the kitchen containing the cooker cooler.

Since heat is being generated from an electric current induced by an electric coil, the range can detect when cookware is removed or its contents boil out by monitoring the voltage drop caused by resistance to the current. This creates possible additional functions, such as keeping a pot at minimal boil or automatically turning off when the cookware is removed.

Contents 1 Benefits 2 Economic considerations 3 Common usage 4 Heat generation 5 Early production 6 Vendors 7 References 8 See also 9 External links

This form of flameless cooking has an edge over conventional gas flame and electric cookers as it provides rapid heating, vastly improved thermal efficiency, greater heat consistency,^[1] plus the same or greater degree of controllability as gas. Water in a pot begins to boil (at its contact points with the pot) in as few as 5 seconds, and then upon turning down immediately (in a second) transitions to simmering.^{[citation needed]}

The amount of time that it takes a pot to boil depends on the power or wattage that the induction hob is using. Thus, the time can be from 3 minutes to around 10 minutes for 3600 Watt to 1200 Watt induction hobs, much faster than conventional electric coil or radiant cookers.

Induction cookers are safer to use than conventional hobs because there are no open flames and the "element" itself reaches only the temperature of the cooking vessel; only the pan becomes hot. Bosch brochures, for example, show a person touching the ceramic cover to the inductor while along side is a pan of boiling water heated by the same induction source. However, it must be remembered that that pan was at 100 °C (212 °F) and in deep fat frying could be as hot as 200 °C (392 °F). Induction cookers are also easier to clean because the cooking surface is flat and smooth, even though it may have several zones of heating induction. In addition, food cannot burn onto the cooking surface as it is not hot.

Induction cookers are considerably more expensive than traditional cookers, but consume half as much electricity as electric-resistance elements and are more efficient in heat transfer, achieving an absolute efficiency of 84% in US Dept of energy tests (compared to a typical 40% for a gas cooker).^{[citation needed]} According to CEG Electric Glass Company, "[Induction cooking] power savings of 40-70% are realistically achievable in comparison to conventional cooktops." CEG Electric Glass Company also states induction cooking has an efficiency rate of 90%, while Electric and Gas have efficiency rates of less than 50%.^[2]

There are, however, single-induction-zone hobs available mostly from Asian suppliers (as opposed to European suppliers). This is due to Asia's more densely populated cities, therefore making this type of induction hob popular where living space is at a premium. Single-zone induction hobs aren't available in retail outlets in North America, but are widely available through online stores and auction sites; some induction hobs selling for as low as $60 USD in Chinatown supermarkets.

Most induction cooking is done on stovetop units, which may be built into a countertop or may be a portable unit. In this style of cooking, the electromagnet is usually sealed beneath a heat-resisting glass-ceramic sheet which is easily cleaned. The pot is placed on the glass coating, and begins to heat up along with its contents. In Japan, a large percentage of rice cookers are powered by induction heating.

An induction cooker works like an electrical transformer: it transfers electrical energy into the pot, using a time-varying magnetic field. A coil of wire is mounted underneath the cooking surface, and a large alternating current is made to flow through that wire. This current creates a changing magnetic field. When an electrically conductive pot is brought close to the cooking surface, this magnetic field induces an electrical current in the pot.

The metal pot is not a perfect conductor, so these eddy currents encounter some electrical resistance. This resistance converts the current into heat. The result is that the metal pot, and only the metal pot, heats up. Heat is transferred from the pot to the food inside the pot by conduction. The cooking surface is designed to be a good thermal insulator, so that a minimum of heat is transferred from the pot to the cooking surface (and thus wasted). In normal operation, the cooking surface stays cool enough to touch without injury.

If the pot is made from an electrical insulator, then no current can flow through the pot. This means that no heat will be generated. Inductive cookers do not work with Pyrex glass or ceramic.

Current is flowing through both the pot and the driving coil; but the pot should heat up, and the coil should stay cool, since any energy that does not go in to heating the pot is wasted. This occurs because the coil and the pot are made of different metals. The coil is typically made from copper, or another metal with high electrical conductivity. The pot is typically made from stainless steel or iron, which is much less conductive. This means that most of the energy will become heat in the high-resistance steel, and the driving coil will stay cool. (The partition of heat is not completely determined by the materials' electrical conductivities. The effective resistance that the eddy current sees is affected by the ferromagnetic steel's permeability, which determines the skin depth. The geometry of the pot and driving coil are also important.)

With aluminum or copper cookware, this is not the case; the current will heat the driving coil just as much as it will the pot. The inductive cooker will therefore not work efficiently.

With iron or steel cookware, some heat is also generated due to the ferromagnetic material's magnetic hysteresis. This is a smaller component (typically less than 7%) of the total heat generated. These two contributions, I²R losses from eddy currents and hysteresis losses, or "copper losses" and "iron losses", are similar to the two identically-named loss mechanisms in an electrical transformer. In a transformer, these losses are undesired, because the useful output is electrical power; in an inductive cooker, the useful output is heat, so these "losses" are what is desired.

The concept of using high frequency magnetic fields to cook with is an old one; first patents date from the early 20th century.

Modern implementation in the USA dates from the early 1970s, with work done at the Research & Development Center of Westinghouse Electric Corporation at Churchill Borough, near Pittsburgh, PA.

This work was first put on public display at the 1971 National Association of Home Builders convention in Houston, TX, as part of the Westinghouse Consumer Products Division display. The stand-alone single “burner” range was named the Cool Top Induction Range. It used transistors developed for automotive electronic ignition systems to drive the 25 kHz current.

Westinghouse decided to make a few hundred production units further to develop the market. These were named Cool Top 2 (CT2) Induction ranges. The development work was done at the same R&D location by a team led by Bill Moreland & Terry Malarkey. The ranges were priced at $1500 each. This price included a set of high quality cookware made of Quadraply, a stainless steel/carbon steel/aluminum/stainless steel laminate (outside to inside).

Production took place in 1973 through 1975, and stopped coincidentally with Westinghouse Consumer Products Division being sold to White Consolidated Industries Inc.

CT2 had 4 burners of sufficient power, about 1600 thermal watts. The range top was a ceramic sheet surrounded by a stainless steel bezel upon which 4 magnetic sliders adjusted 4 corresponding potentiometers set below. This design, using no through-holes, made the range proof against spills. The electronic section was made in 4 identical modules. Provision was made for fan cooling of the electronics.

In each of the electronics modules the 240V 60Hz domestic line power was converted to 20V to 200V continuously variable DC by a phase-controlled rectifier. This DC power was in turn converted to 27 kHz AC by 2 arrays of 6 paralleled Motorola automotive ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator of which the inductor component was the induction heating coil & its load, the cooking pan.

Control electronics included functions such as protection against over-heated cook-pans & overloads. Provision was made to reduce radiated electrical & magnetic fields. There was magnetic pan detection also.

CT2 was UL ® Listed and received FCC approval, both firsts. Numerous patents were issued.

Raymond Baxter demonstrated the CT2 on his BBC series, Tomorrow’s World. He showed how the CT2 could cook through a slab of ice.

Market for induction hobs is dominated by German players, such as AEG, Bosch, Miele, and Siemens. The Italian firm Smeg is also a key player in this market. Prices range from about GB£400 to 1000. In 2006, Stoves launched the UK's first domestic induction hob on a range cooker.

Taiwanese and Japanese electronics companies are the dominant players in induction cooking for East Asia. Certain companies have also started marketing in the West; such as Tatung, Sunpentown, Panasonic and Hitachi. However, their products available in Western markets are a small fraction of what is available in their home markets. Interestingly, some Japanese electronics giants only sell domestically. Some of the brands on the retail market in the Western U.S. are Thermador, GE Profile, KitchenAid, and Jenn-Air (Whirlpool Corp), all with 30" and 36" kitchen counter-top models.

Small stand-alone induction hobs are relatively inexpensive, around US$60.

Units may have two, three, four or five induction zones, but four is the most common. Some have touch sensitive controls. Some induction stoves have a memory setting, one per hob, that is able to time the amount of heat required.

• Glass-ceramic
• Microwave oven

• US Department of Energy- Technical Support Document for Residential Cooking Products
• PATH Technology Inventory: Induction Cooktops
• [1] - Induction Cooking Explained
• Cooktek - Induction Cooktops and Chafers
• [2] - Thermador
• [3] - GE Profile