CHAPTER I
The Problem and Its Setting

Introduction Cookers can broadly be divided into two types, namely gas cookers and electric cookers. Electric cookers can also however also be sub-divided into three types, namely radiant coil cookers, solid disc cookers and ceramic top cookers. Gas cookers power is easy to adjust and response is instant, thus providing good temperature control. Consumption of gas varies depending on the size of the burners. This type of cooker is the least efficient of all the cookers. The main advantage of a gas cooker is that gas is relatively inexpensive. The main disadvantage is that these types of cookers are the least safe out of all the cookers. Radiant coil cookers are the most common of all the cookers. They are also the cheapest cookers to purchase initially. These types of cookers are heated by electrical resistance. These cookers are more efficient than solid disc cookers and ceramic top cookers. Solid disc cookers are similar to radiant coil cookers. They are just solid and fixed to the cooker. They do not need to be removed for cleaning. These elements have a greater thermal mass than radiant coil elements and are thus less efficient and have a slower response time. Ceramic top cookers have their elements below heat resistant ceramic glass. This improves appearance and improves cleaning. These types of cookers take longer to heat up than radiant coil and solid disc cookers. Their response is also slower than the above-mentioned cookers.

The main function of the cooker is to heat the vessel in which the food is. This vessel in turn distributes the heat to the food and cooks it. Such cooking can amount to as much as 10% of all energy used in a household. By utilizing this energy efficiently the energy used for cooking can be substantially reduced. Most cookers expend wasted energy in the form of heat .Cookers have always been designed to generate heat in a manner that will most efficiently transfer this heat to the cooking vessel. Conventional cookers such as gas and ‘electric resistance’s cookers lose a lot of energy to the environment in the form of heat, as the heat must be transferred from the ‘element’ to the cooking vessel. This heat loss results in poor thermal efficiency.

Due to the nature of induction heating all the heat that is generated by the induction cooker is generated within the cooking vessel, thus the thermal efficiency of the induction cooker is far greater than conventional cookers. This results in quick rise in temperature, which in turn results in reduced cooking times. If the cooking vessel is removed from the cooker the power is instantly reduced to a minimum. As the heat is generated in the cooking vessel and not the element, the surface of the cooker remains relatively cool. The only heat is that which is transferred from the cooking vessel to the cooker. Induction heating involves the varying of the magnetic fields in the primary, thus inducing circulating eddy currents, caused by electromagnetic induction, in the secondary.

In the case of the induction cooker the cooking vessel acts as a short-circuited secondary, and the induction coil acts as the primary. Induction heating can be defined in the following manner: by varying the current in the primary circuit an alternating magnetic field is setup. When a conductive material (the cooking vessel in the case of the induction cooker) is placed within this alternating magnetic field, eddy currents are induced in the conductive material. Due to the resistivity of the material, the eddy currents will cause conduction losses in the material, leading to heat being generated within the material. Induction heating employs three main effects, namely electromagnetic induction, skin effect and heat transfer. Induction heating allows a defined section of the vessel to be heated accurately. The skin effect allows the penetration depth of the magnetic field to be controlled, thus ensuring maximum heat transfer.

Induction cookers are a relatively new application of induction heating. Induction cookers do not work on the same principal as other cookers. They do not generate heat, which is then transferred to the cooking vessel. Induction cookers work on the principal that they generate the heat in the cooking vessel itself. This improves the transfer of energy and reduces the amount of wasted energy normally associated with conventional cookers.

Background of the Study Induction cooking uses induction heating to directly heat a cooking vessel, as opposed to using heat transfer from electrical coils or burning gas as with a traditional cooking stove. For nearly all models of induction cooktop, a cooking vessel must be made of a ferromagnetic metal, or placed on an interface disk which enables non-induction cookware to be used on induction cooking surfaces.
In an induction cooker, a coil of copper wire is placed underneath the cooking pot. An alternating electric current flows through the coil, which produces an oscillating magnetic field. This field induces an electric current in the pot. Current flowing in the metal pot produces resistive heating which heats the food. While the current is large, it is produced by a low voltage.
The magnetic properties of a steel vessel concentrate the induced current in a thin layer near its surface, which makes the heating effect stronger. In non-magnetic materials like aluminum, the magnetic field penetrates too far, and the induced current encounters little resistance in the metal. At least one high-frequency "all metal" cooker is available, that works with lower efficiency on non-magnetic metal cookware.
An induction cooker transfers electrical energy by induction from a coil of wire into a metal vessel that must be ferromagnetic. The coil is mounted under the cooking surface, and a large alternating current is passed through it. The current creates a dynamic magnetic field. When an electrically conductive pot is brought close to the cooking surface, the magnetic field induces eddy currents in the pot. The eddy currents flow through the electrical resistance of the pot to produce heat; the pot then in turn heats its contents by heat conduction.
The cooking vessel is made of stainless steel or iron. The increased magnetic permeability of the material decreases the skin depth, concentrating the current near the surface of the metal, and so the electrical resistance will be further increased. Some energy will be dissipated wastefully by the current flowing through the resistance of the coil. To reduce the skin effect and consequent heat generation in the coil, it is made from litz wire, which is a bundle of many smaller insulated wires in parallel. The coil has many turns, while the bottom of the pot effectively forms a single shorted turn. This forms a transformer that steps down the voltage and steps up the current. The resistance of the pot, as viewed from the primary coil, appears larger. In turn, most of the energy becomes heat in the high-resistance steel, while the driving coil stays cool.
The cooking surface is made of a glass-ceramic material which is a poor heat conductor, so only a little heat is lost through the bottom of the pot. In normal operation the cooking surface stays cool enough to touch without injury after the cooking vessel is removed.
New types of power semiconductors and low-loss coil designs have made an all-metal cooker possible, but the electronic components are relatively bulky. Panasonic Corporation in 2009 developed a consumer induction cooker that uses a higher-frequency magnetic field, and a different oscillator circuit design, to allow use with non-ferrous metals.

Objectives of the Study
General Objectives The main purpose of this study is to design and construct a three way input source induction cooker using 12 volt DC such as batteries, as an alternate source from a 220/110 AC input usually coming from a wall outlets in our homes. It can be recharge using solar panel or using a built in charger circuit for its convenience for long travels and the like. Performance testing will be conducted on the functionality of the device, application and safety.

Specific Objectives A three way input source induction cookers with solar based charger aims to reach high efficient, low initial cost and reliable cooker to satisfy the needs of the users. It must be controllable temperature range in the output power to be operated with all kinds of vessels such as steel, stainless steel, aluminum, alloy and combinations.

Scope and Limitation
The study covers the construction of an induction cooker with a three way input source that can be recharged using a solar panel and a built in charger circuit. It is limited on the heat generated by electromagnetic currents in the burners that respond to metal cooking pots and pans, often referred to as heatless cooking. It doesn’t require an open gas flame or red hot electric coils. The study briefly introduces its fundamental principle, research background and the motivation of the development of a non-magnetic material induction cooker.
It will be materializing an induction cooker available in the market generated from an AC outlet and will be modified using series resonant inverter topologies to convert AC to DC and a voltage multiplier to increase the frequency and voltage output. It can only conduct energy by magnetic induction. Induction can heat food only through pans made of steel or iron. Not all stainless steel cookware is compatible with induction cooking. Glass and ceramics are unusable, as are solid copper or solid aluminum cookware for most models of cooker. Cookware must have a flat bottom since the magnetic field drops rapidly with distance from the surface. Induction disks are metal plates--much like a skillet with no sides--that heat up non-ferrous pots by contact, but these sacrifice much of the power and efficiency of direct use of induction in a compatible cooking vessel.
A small amount of noise is generated by an internal cooling fan. Audible noise (a hum or buzz) may be produced by cookware exposed to high magnetic fields, especially at high power if the cooker has loose parts. Some users may detect a whistle or whine sound from the cooker, or from the power electronic devices. Some cooking techniques available when cooking over a flame are not applicable. Persons with implanted cardiac pacemakers or other electronic medical implants are usually instructed to avoid sources of magnetic fields; the medical literature seems to suggest that proximity to induction cooking surfaces is safe, but they should always check first with their cardiologists. Radio receivers near the unit may pick up some electromagnetic interference.
An induction stove will not operate during a power outage. Older gas-stoves do not need electric power to operate; however, modern gas-stoves with electrical ignition require an external ignition source (e.g. matches) during power outages.

Significance of the Study A three way input source induction cooker which can work for non-magnetic material cookware such as aluminum and copper, can be very competitive in the market. This benefits everyone, from the fact that people’s primary need is food. Cooking food at home is the single most important thing you can do for your health and the health of your family.

In the food service industry time is money, and a faster cooking surface results in shorter preparation time. And we all know what that means increased profits. Because energy is directly transferred within the pan metal, cooking on an electric induction range is extremely fast - even faster than gas.
This is safe to be used by younger generation even children at home. Electric induction cook tops are much safer than gas or other electric surfaces, since there is no open flame, red-hot coil or other radiant heat source to ignite fumes or flammable materials.
For moms at home, this cooker is cleaner and cooler with no grates or grease catch to worry about, clean up is a breeze. Just use a damp cloth and wipe over the flat, easy-to-clean surface. Traditional gas or electric ranges waste up to than half the heat they generate. The waste heats the kitchen instead of the food and contributes massively to structural cooling costs. With an electric induction range, almost no ambient heat is produced, since all the heat is being generated in the pan itself. It is a convenient cookware when a power outage occurs in homes.
This is significant in such way that it is cheaper. Induction cooking is far more energy efficient than gas or traditional electric ranges. In fact, when using an electric induction cooktop, 90% of every peso you spend on energy goes right where you want it - in the pan! Gas delivers only 55% to the pan and traditional electric about 65%. In addition, when you remove the pan from the induction cooking surface, the induction cooktop immediately goes into standby mode, which uses almost no energy.
These appeals to chefs, caterers, and even home cooks. Induction burners won’t heat up your kitchen. Food spills and boil-over aren’t burned on to the stove and are easily wiped off. Most stove-tops are either easy-to-clean glass or ceramic. In addition, you can leave the pot on the burner after cooking without having to worry about excess heat burning your food.
This prototype is convenient to travellers. It is specially design for bringing it anywhere without open gas flames, this is a rechargeable electronic device and can be operated also by a simple battery of 12volt. The biggest difference between induction cooking and other methods is where the heat is actually generated. Gas and electric stovetops produce heat on a burner. This heat is then transferred to a cooking pan and then its contents. In contrast, induction stove tops generate heat in the vessel. There is no transfer from the burner to the pan. Thus there is virtually no wasted heat. According to studies, induction cooking is about 90% efficient, compared to electric and gas cooking that have 47% and 40% energy efficiency rating respectively.