Induction cooker
From Wikipedia, the free encyclopedia
An induction cooker uses induction heating for cooking. This heat is the result of magnetic field hysteresis loss. A conducting pot is placed above an induction coil for the heating process to take place. This type of cooktop does not work with cooking vessels that are constructed from non-magnetic materials (e.g., aluminum or glass) . Unlike alternatives such as electric hotplates and open-grills, an induction cooker creates no heat; only the vessel used for cooking is heated.
Induction cookers are faster and more energy-efficient than traditional cooktops. Unlike traditional cooktops, the pot itself is heated to the desired temperature rather than heating the stovetop, reducing the possibility of injury. Skin can be burned if it comes into contact with the pot, or by the stovetop after a pot is removed. Unlike a traditional cooktop, the maximum temperature in the system is that of the pot, which is much less capable of causing serious injury than the high temperatures of flames or red-hot electric heating elements. The induction cooker does not warm the air around it, resulting in added energy efficiency.
Since heat is being generated from an induced electric current, the range can detect when cookware is removed or its contents boil out by monitoring the voltage drop caused by resistance in the circuit. This allows additional functions, such as keeping a pot at minimal boil or automatically turning off when the cookware is removed.
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[edit] Benefits
This form of flameless cooking has some advantages over conventional gas flame and electric cookers as it provides rapid heating, improved thermal efficiency, greater heat consistency, plus the same or greater degree of controllability as gas.[citation needed] In situations in which a hotplate would typically be dangerous or illegal, an induction plate is ideal as it creates no heat itself.
The amount of time that it takes a pot to boil depends on the power of the induction cooktop. Thus, the time can be from three minutes for 3600 watt induction stove tops, to around ten minutes for 1200 watt ones. However, boiling water is a process largely dependent on the amount of water; the speed benefits of induction cooking are most often seen when stir-frying: a thin pan with 3 tablespoons of oil may heat up to stir-frying temperature in as little as 10 seconds.
Induction cookers are safer to use than conventional stoves because there are no open flames and the "element" itself reaches only the temperature of the cooking vessel; only the pan becomes hot. Induction cookers are 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.
[edit] Drawbacks
Induction cookers have some drawbacks. For example, cookware must be made of ferrous materials; they do not work with non-magnetic materials, such as aluminum, glass or ceramic.
Since the heat up time is almost instantaneous, cooking with thin-bottomed pans requires additional attention to avoid burning food. The temperature is controlled by switching on and off the magnetic field, rather than changing its intensity. Hence, the cookware heats up and cools rapidly, causing temperature extremes. An induction cooker works well with a flat-bottomed pan. Curved pans, such as woks (despite companies selling 'induction compatible' ones), require a curved surface Chinese Style Induction Cooker.
Pans placed on an induction cooker must contain oil or a liquid to absorb the heat; otherwise, the rapid increase in temperature will cause food to burn. Anyone with a pacemaker or defibrillator should not use one of these stoves as it may cause complications with such electrical devices.
Also, induction cookers are on average more expensive than electric cooktops.
[edit] Economic and environmental considerations
Induction cookers are getting popular and less expensive than traditional cookers. According to the Department of Energy, the efficiency of energy transfer for an induction cooktop is 84%, versus 71% for a smooth-top non-induction electrical unit, for an approximate 20% savings in energy for the same amount of heat transfer.[1] See Table 1.7 of the DoE reference.
There are cheaper single-induction-zone cooktops available largely from Asian suppliers. This is due to Asia's more densely populated cities, therefore making this type of induction cooker popular where living space is at a premium.[citation needed] Single-zone induction cookers are available only in few retail outlets in North America, but are widely available through online stores and auction sites; some induction hobs sell for as low as $60 USD in supermarkets.[citation needed] Twin Zone Cookers also made available these days and they are gradually gaining momentum in Japan, Taiwan, Hong Kong.
[edit] Common usage
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 that 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[citation needed]. In Hong Kong, power companies recommend a number of models for ready selection which are safe, clean, energy efficient and easy to install[citation needed].
[edit] Heat generation
Induction stoves work with high frequency magnetic fields, rather than resistance. A coil made of copper tubing is mounted underneath the cooking surface. Alternating current in this coil produces the varying magnetic field, that is responsible for hysteresis loss heating of the pot material.
Pots made from electrical insulators or aluminum will as a rule not heat up on inductive cookers. Only cookware of ferromagnetic materials with the correct skin depth can sufficiently absorb the magnetic field and produce hysteresis loss. The materials in this type of cookware have a ferritic structure; iron, including cast iron, carbon steel, and some stainless steels can be heated by magnetic induction. However, many stainless steels (having nickel in their alloy causing an austenitic structure) and other materials that are non-magnetic will not heat up on an induction cooktop.
Contrary to popular belief, the principle of electric heating via eddy current loss does not require magnetic materials, as any conductor is capable of heat generation via eddy current heating. Theoretically it is possible to make an induction stove that works with aluminum pots via Eddy current loss. In practice however it is easier to build one that uses magnetic hysteresis loss, and this is therefore the most common type of induction cookware.
[edit] Early production
The concept of using high frequency magnetic fields to cook with is an old one; first patents date from the early 1900s.[citation needed]
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, USA.[citation needed]
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.[citation needed] 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 and 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 four burners of sufficient power, about 1600 Watts. The range top was a ceramic sheet surrounded by a stainless steel bezel upon which four magnetic sliders adjusted four corresponding potentiometers set below. This design, using no through-holes, made the range proof against spills. The electronic section was made in four 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 two arrays of six 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 and its load, the cooking pan.
Control electronics included functions such as protection against over-heated cook-pans and 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 also 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.
Sears Kenmore sold a free-standing oven/stove with four induction cooking surfaces in the mid-1980s. Model Number 103.9647910. The unit also featured self-cleaning oven, solid-state kitchen timer and capacitive-touch buttons (very advanced for its time). The units were more expensive than standard cook tops, but were still affordable for a middle-class family.
[edit] Vendors
Market for induction stoves is dominated by German players, such as AEG, Bosch, Miele, Schott AG and Siemens. The Spanish-French company Group Fagor-Brandt, Italian firm Smeg and Sweden's Electrolux are also key players in the European market. Prices range from about GBP250 to 1000 within the UK. In 2006, Stoves launched the UK's first domestic induction hob on a range cooker at a slightly lower cost than those imported.
Taiwanese and Japanese electronics companies are the dominant players in induction cooking for East Asia. After aggressive promotions by utilities in HK like CLP Power HK Ltd[2], many local brands like icMagIC[3], Zanussi, iLighting, German Pool [4]also emerged. Their power and ratings are high, more than 2800 W. They are multiple zone and capable to perform better than their gas counterpart. The efficiency is as high as 90% and saves a lot of energy and environmentally friendly. Their use by local Chinese for wok cooking is getting popular. Some of these 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 US are Wolf, Viking, Thermador, GE Profile, KitchenAid, and Jenn-Air (Whirlpool Corp), all with 30" and 36" kitchen counter-top models.
Small stand-alone induction cookers are relatively inexpensive, around US$60.
Units may have two, three, four, or five induction zones, but four is the most common in US, two is most common in Hong Kong, three is most common in Japan.. Some have touch-sensitive controls. Some induction stoves have a memory setting, one per hob, to time the amount of heat required.
