BACKGROUND ART Electrically powered heating devices are well known and popular in both industrial and domestic applications. Electrical heating devices can be powered from any conveniently located electrical energy outlet and provide almost instantaneous heat as and when required.

Numerous types of electrical heating devices have been developed, from fan heaters to under floor or ceiling mounted heaters. However, in most instances these devices are all run from a mains voltage AC power source.

Existing surface heating devices are not readily portable as in most instances they need to be connected to a mains voltage power supply. Further, relatively thin wires may be used as heating elements in these devices. The thin wires used must be fixed and held rigidly in place and supported (usually in a housing) to ensure they cannot be broken or damaged. This configuration of heating device creates problems when a portable unit is required, as a strong and bulky housing also needs to be included to protect the delicate wires used.

A surface heating device that can be simply constructed, which is portable and can be used in a large number of locations would be of great advantage over the prior art.

Specifically - an improved surface heating apparatus which can be moved and handled without fear of damaging the apparatus and which can be powered by an extra low voltage direct current electrical energy supply would be of great advantage over the prior art.

"Extra low voltage"is defined in the New Zealand Handbook for Electrical Wiring Regulations as"not exceeding 32 volts alternating current or 50 volts direct current".

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description that is given by way of example only.

DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a heating apparatus which includes, two or more connection terminals adapted to connect with a source of electrical energy with a voltage of less than 50 volts, and at least one heating element constructed from an electrical conductor with a width of at least 0. 4 mm, and a cover adapted to at least partially enclose said heating element or elements.

According to another aspect of the present invention there is provided a heating apparatus substantially as described above, wherein the cover is adapted to support and retain a heating element enclosed within said cover to provide the heating apparatus with portability.

A heating apparatus configured in accordance with the present invention may be any type of device that can be electrically powered to emit heat. In a preferred embodiment a heating apparatus constructed in accordance with the present invention may also be portable to allow heat energy to be supplied to the user in a wide variety of locations.

In a further preferred embodiment each of the connection terminals may be adapted to supply electrical energy with a voltage less than 50 volts to at least one heating element incorporated in to the apparatus.

In a preferred embodiment a heating element of the present invention is adapted to receive electrical energy from an electrical energy supply which supplies direct current at a voltage less than 50 volts.

This type of energy supply allows the present invention to be used in a large number of locations. In some instances AC mains power may not be available at a particular location, whereas a 12-volt DC power supply may be obtained from a car battery, an array of solar cells or a wind, fossil fuelled or water powered generator. A low voltage direct current may also be easily obtained with use of a simple and well-known transformer arrangement used to step down and rectify an AC mains voltage.

Those skilled in the art should appreciate the present invention may be configured to provide different levels of heat output in different embodiments.

In a preferred embodiment the present invention may be constructed with two capacities being either a high capacity embodiment or a low capacity embodiment. In a high capacity embodiment the present invention may be adapted to emit at least 150 watts of heating power whereas in a low capacity embodiment the present invention may be adapted to emit less than 150 watts heating power.

In a preferred embodiment where the heating apparatus is configured to emit over 150 watts, the heating element may be constructed from a ferrous mesh of physically and electrically connected wires of 0. 55 mm diameter at 25 mm centres each way or 0. 4 mm diameter at 12. 5 mm centres each way sandwiched into a cover. A good example of this type of heating element is given in PCT Patent Application No.

PCT/NZ95/00108.

For portable heaters with a capacity of under 150 watts, one or more lengths or loops of wire within a cover may be used. Because a length of wire is used, the ability to weld to the heating element is not so important and ferrous wire is not necessarily preferred. The much lower currents required for an under 150 watt capacity heater do not necessitate a heat sensitive fuse to detect failure of the joint between the heating element and a connection terminal, since fire safety can be ensured preferably having the joint within a small fireproof enclosure. The feature of a lower capacity heating apparatus means that it can be rolled up and delivered by post in standard postage tubes or folded and sent as a small parcel.

A heating element used in conjunction with the present invention may be any type of electrical conductor, which, due to its electrical resistance, produces heat energy when an electrical current is run through it. As can be appreciated by one skilled in the art the resistance of the conductor used and the length of the conductor over which an electrical current is applied, coupled with the electrical energy applied to the conductor will determine how much heat is produced.

A preferred material for construction of the heating element is ductile steel that has very high physical strength together with a suitable electrical resistance. This means the physically weakest link in the low voltage circuit is the connections which may be positioned at each end of the heating element. Having a known weak point provides the advantage of allowing fusing to be installed in a position where damage that could become a fire risk will be detected and repaired.

In some embodiments, a spiral shaped heating element may be manufactured from galvanised or stainless steel sheeting. The advantage of forming the heating element into a spiral is that this improves the flexibility of the heating apparatus helping it to lie flat when configured according to the different aspects of the present invention.

In a preferred embodiment a heating element used in conjunction with the present invention may be identical to or similar to the heating element described in PCT Patent Application No. PCT/NZ95/00108. This configuration of heating element ensures that there is a relatively even distribution of heat produced by the heating element over its length, and also conducts electricity around any hot spots formed on the heating element. Further details and advantages of this type of heating element are discussed in full in the above patent specification.

Alternative embodiments may not employ a substantially regular mesh shaped heating element as discussed in PCT Patent Application No. PCT/NZ95/000108. For example in one alternative embodiment a single wire may be used to provide heat to an area by arranging the wire so that it does not cross over itself to provide a short circuit. The positioning and arrangement of the wire or multiple wires may be determined by the wire's length and the area that is to be heated by the heating apparatus.

In another alternative embodiment a thin layer of conducting material may be used as a heating element. For example, in one embodiment a layer of aluminium foil may be used as the thin layer of conductive material. This foil may be laid out to cover the same area as that to be heated and then possibly have a number of separating tracks cut or etched from the surface of the foil. This type of heating element provides a relatively wide conductor and also allows relatively quick and inexpensive manufacturing of the heating element.

Preferably, the heating apparatus in low capacity embodiments may be adapted so that it may be folded.

Preferably, the thickness of the mat when folded may be 10 millimetres or less.

Preferably, the heating apparatus may be operable while folded. The heat output may be preferably determined by the unit area heated.

If the present invention is operated as a single layer, then the heat output per unit area will be at a lower level than if the present invention is folded in accordance with the above preferred embodiment, to give multiple thicknesses.

Preferably, the hinge of the folding portion may include a crinkled heating element.

This has the advantage that the fatigue in the mesh from being repeatedly folded is reduced.

In a further preferred embodiment three or more points on the length of a heating element may be capable of connection to connection terminals, or a switch or other linking element which will in turn connect the selected point on a heating element to a connection terminal. This arrangement of the present invention allows the heat output of the heating apparatus to be varied relatively easily. As the length of the heating element over which electrical energy is supplied influences the amount of heat produced, changing the length of heating element over which electrical energy is supplied will change the amount of heat produced.

In a preferred embodiment the width of a conductor used in a heating element is greater than 0. 4 mm. This minimum conductor width ensures that the heating element can readily receive and transport DC electrical energy of less that 50 volts. These specified dimensions of the heating element conductor also ensures that the heating element has a high structural strength and integrity, allowing it to resist damage from accidental knocks or impacts when transported.

In a further preferred embodiment a conductor used in a heating element may have a width of approximately 0. 7 mm. This width has been found by the applicants to provide the required structural strength and integrity for the conductor and to provide the required electrical and thermal properties for the conductor used. However, it should be appreciated by those skilled in the art that reference to a conductor with a width of 0. 7 mm only should in no way be seen as limiting. The applicants have found that a conductor with a width between 0. 4 mm and up to 3 mm may still function effectively in accordance with the present invention, and reference throughout this specification only to 0. 7 mm wide conductors should in no way be seen as limiting.

For example, in some embodiments the greater flexibility of 0. 4mm conductor may be preferred.

The heating apparatus also includes a cover. This cover is adapted to at least partially enclose the invention's heating element or elements.

In a preferred embodiment the cover is adapted to fully enclose and surround a heating element used in conjunction with the present invention. This configuration of the cover allows the cover to retain and support a heating element in place, preventing the heating element from shifting out of position and short-circuiting or breaking during transportation or use.

In a preferred embodiment the cover used may be constructed from materials which allow an even distribution of heat from the heating element through to the outer surface of the cover. In a further preferred embodiment the material used in the construction of the cover may also be selected to increase the structural strength and integrity of the heating apparatus, or to prevent damage to the device when it is walked over or moved.

For example in some embodiments rubber or plastic material such as PVC may be used in construction of the heating apparatus to provide it with a relatively high degree of structural strength. In such an embodiment the heating element may also be constructed from steel, thereby providing additional structural strength to the finished heating element.

This configuration of the invention means that it can be used as a portable heating apparatus. The structural strength provided by the cover means that the invention may be dragged around, stood on, folded up or crushed without serious risk of the heating element or elements breaking. Further, any distortion caused in the heating elements through an impact or other blow can easily be moulded and bent back into the original shape of the heating element.

In a preferred embodiment the cover used may be formed from a substantially flexible material. A flexible cover ensures that the heating apparatus may be bent, folded up or moulded and fitted on to a number of surfaces as and when required. This is of advantage for a portable heating apparatus where the flexibility of the cover ensures that the heating apparatus may be used in a wide variety and number of locations.

In a preferred embodiment the heating element or elements used in the construction of heating apparatus may be glued to a non-conductive net, mesh, cloth or film to form one side of the cover. For example, in some embodiments the non-conductive material used may be formed from hemp, fibreglass, plastic or rubber to form one side of the cover. A mouldable material such as plastic or rubber may be then moulded around the open side of the heating element to form the required enclosing cover.

In an alternative embodiment heating elements may be placed on a continuous length of non-conductive film, mesh, net or cloth with the connection terminals protruding out from the side of the film. A second non-conductive layer of mouldable material may then be laminated onto the heating elements, again to form the required enclosing cover. Portions of the continuous length of film may be cut to the required size and shape to form the heating apparatus.

In a further preferred embodiment the bottom layer of the cover may include a number of raised projections or ribs. These projections provide extra support in and around the area where the heating element conductors lie in the cover to increase the structural strength of the heating apparatus and provide resilience underfoot.

In yet another preferred embodiment where a cover is constructed from two layers of material, the first layer of the cover formed may be constructed from a heat insulating material, while the second opposite layer used may be formed from a material which is a good conductor or radiator of heat. In such an embodiment the heating element enclosed by the cover will form the middle layer of a three-ply laminate of cover faces and heating element. For example, in one embodiment a cover may be constructed from a fibre matting on one side and a dark latex or vinyl overlay on the other side of the cover.

In a preferred embodiment the cover used in accordance with the present invention may include rubber. Rubber provides the required flexibility, structural strength and heat transportation characteristics required by the present invention. However, alternative embodiments may not employ rubber as the material used in the construction of a cover. For example in other embodiments plastics materials such as polyurethane, polythene or an organic fabric may be used in the construction of a cover, and reference to the use of rubber only should in no way be seen as limiting.

In some embodiments, the heating apparatus may be manufactured to be approximately two millimetres in thickness or less.

As can be appreciated by one skilled in the art, due to the extra low voltage energy used in the apparatus only a thin film of material needs to be applied to heating elements to act as a cover. The extra low voltage of the supplied energy ensures that there is little danger of electric shocks being delivered to the user or the heating apparatus accidentally starting a fire.

According to one aspect of the present invention there is provided a method of manufacturing a heating apparatus characterised by the steps of : (a) forming a heating element from an electrical conductor with a width of at least 0. 4 millimetres, and (b) attaching two or more connection terminals to points on the heating element, and (c) enclosing the heating element in a cover to support and retain the heating element in place.

According to another aspect of the present invention there is provided a method of manufacturing a heating apparatus characterised by the steps of (a) forming a heating element constructed from an electrical conductor with a width of at least 0. 4 millimetres, and (b) attaching two or more connection terminals to said heating element, and (c) applying the heating element to a continuous length of thermally insulative material, and (d) laminating a layer of thermally conductive material on top of the heating element to enclose the heating element between the thermally conductive and insulative layers, and (e) cutting the cover material to form a heating apparatus of a required length and size.

In a preferred embodiment, the heating element may be attached or moulded to the cover in the following way : A length of heating element may be woven between at least two alternate pulleys.

Alternate pulleys may be separated forming a gap between the alternate pulleys, which draws a length of heating element across the gap formed by the widened pulleys. Sheets of material may be placed above, below, or above and below the heating element length and fused together by some means.

Preferably, the sheets may be manufactured from polyvinylchloride (PVC).

Preferably, the above method may be further characterised in that the edges may not be fused until the pulleys are removed from the turning points and then the ends fused.

Preferably, the sheets may be fused together using hot air, although this should not be seen to be limiting as other methods of fusing the sheets may be employed such as adhesive, sealant, and other heat sources and so forth.

In further preferred embodiments, the conductive wire of the heating element may be manufactured from a material that is able to be gripped by a magnet.

In some preferred embodiments, the method used to mould or attach the heating element to the cover may involve using a magnetic force to hold the conductive length in position during the attachment process.

In a preferred embodiment the present invention may also include an adapter or an arrangement of electrical transformers which allow electrical energy of less than 50 volts to be supplied to the heating apparatus from a source of electrical energy with a voltage greater than 50 volts. However, in an alternative embodiment the present invention may also include a source of electrical energy with a voltage of less than 50 volts.

In a preferred embodiment the heating apparatus may also be associated with an electrical energy supply transformer.

In a further preferred embodiment the transformer associated with the apparatus may be any double wound isolating transformer capable of converting a particular mains voltage power supply to an electrical energy supply of under 50 volts. Those skilled in the art should also appreciate that the double wound isolating transformer referred to above may be used where the heating apparatus is designed to have a relatively high maximum heat output. Those skilled in the art should appreciate that other types of transformers or alternative similar devices may be used in conjunction with the present invention. For example, in one alternative embodiment where a relatively low maximum heat output is required from the heating apparatus, a small low voltage transformer may be provided within a cord used to connect the heating element and connection terminals to a supply of electrical energy. In this instance, a low voltage electronic transformer similar to that marketed by Light Tech Industries Limited of Rishon Lezion, Israel, may be used.

In some preferred embodiments the transformer may incorporate the use of a ledge in the transformer housing that holds the transformer in position.

Preferably, this position may be a position that results in the suspension of the coils off the housing floor.

The ledge may also provide for a means of gripping the transformer, which may result in improved portability.

The ledge in the transformer may also improve the rigidity of the sides of the housing.

Preferably, the transformer output may include a junction formed within the transformer housing.

Preferably the present invention includes two or more connection terminals to connect the heating apparatus to a source of electrical energy.

The two or more connection terminals may be standard electrical connectors well known in the art. These connectors may be adapted to allow quick and simple connection of the present invention to a source of low voltage electrical energy. In a further preferred embodiment each of the connection terminals used may be adapted to supply electrical energy with a voltage less than 50 volts to at least one heating element incorporated in to the apparatus.

In a preferred embodiment a connection terminal may be constructed from a copper lead brazed or welded to a particular point on a heating element. The copper lead can then have its free end formed into a pin adapted to slot into a socket or adaptor in a power supply transformer. The copper leads used may have a similar cross section to the total cross section of a conductor used in a heating element and may also have the majority of the lead length insulated with a plastic or rubber material.

In one embodiment, the ends of a heating element may be associated with or include clips or plugs.

Preferably, these clips or plugs may incorporate a weight of metal to absorb and distribute heat. This is an advantage in that any heat generated from a poor connection may be distributed and absorbed by the metal, preventing a breakdown of the connection, and also by reducing the risk of a fire from a poor connection.

In an alternative embodiment an electronic transformer may be fitted into a flexible power lead permanently fixed to or incorporated into at least one connection terminal of the apparatus. This flexible power lead may be made up from a standard flexible cord with a moulded plug connected to an electronic transformer. From the low voltage end of the electronic transformer the cable can continue as an extra low voltage, high current flexible cord which can have a socket to receive the two pins brazed or welded in place in the socket.

In one embodiment the present invention may also incorporate a dimmer switch connected to an electronic transformer. This dimmer switch may be used by the operator to control either the voltage or the current of electrical energy supplied to the heating apparatus.

In some embodiments the present invention may also be provided a heat sensitive fuse to protect against overheating of lead connections. This fuse may be an in-line fuse within a connection terminal, an electronic sensor within the transformer or an additional circuit alongside the extra low voltage end of the transformer output cable that triggers a fuse or switch in the transformer.

In some embodiments the fuse parameters may be chosen to prevent overheating in the junction between a connection terminal lead and the heating element.

In other embodiments, a heat sensitive switch may be used in place of such a fuse. For example, in one embodiment a bi-metallic switch can be used instead of a heat senstive fuse.

In some embodiments the transformer may also include a power output control circuit controlled by a thermostat incorporated into a transformer or a connection terminal.

This circuitry may set a minimum and maximum level of heat to be produced by the heating apparatus and regulate the supply of electrical energy with regard to same.

In a preferred embodiment an iron core transformer associated with the heating apparatus in high capacity embodiments may be specifically adapted to be safe and portable. Such a transformer may include both its primary and secondary coils sealed within a single housing as well as a heat sensitive fuse that may cut the primary coils input power if - a loose connection causes overheating, or - a short circuit overload occurs which is too minor to blow an additional current sensing fuse located in the transformer but is sufficient to result in the transformer heating, or - the transformer is overheated by, for example, having an insulating material such as a coat or a blanket thrown over the transformer.

Preferably, a heat sensitive fuse may be located within the housing, whose failure will result if a faulty connection to the output lead causes the junction to overheat.

The connections and components of the transformer may also be adapted so that the heat sensitive fuse discussed above is located near the top of the transformer housing so that it will be in the hottest place of the housing.

In some embodiments the supply transformer may also include alternating current rectification circuitry. Such circuitry will allow the heating apparatus to be supplied with energy from an AC mains power distribution network, and for a heating element to receive DC electrical energy of less than 50 volts.

This configuration of the present invention means that it is not limited to use only with an AC mains powered or low voltage DC electrical energy. The present invention may be used in any location where there is a DC battery with a voltage less than 50 volts or other alternative DC electrical energy supply with a voltage less than 50 volts. In most instances a generator (such as that provided on a vehicle) is available when AC mains power is not. The present invention may also be used wherever there is an AC mains powered electrical energy supply as well.

The present invention provides many advantages over existing heating devices.

The heating apparatus discussed above may be easily transported to a number of different locations and also powered using readily available extra low voltage DC energy supplies. For example the present invention may be easily powered from the battery of a vehicle, charged by a combustion engine, or wind or water powered generators - or alternatively could be powered using an adapter connected to a standard AC mains power source. A further advantage of the present invention is that the cover does not have to be moisture-proof. The present invention is configured so that an extra low voltage can be used. Thus, moisture or water will not cause a short circuit.

The physical dimensions of the conductor used in a heating element greatly reduced the chances of the heating element being damaged during use or transportation because of its relatively high structural strength and integrity.

The cover used in accordance with the present invention ensures that the heating apparatus may be used in a wide variety and a number of locations, allowing the heating apparatus to mould itself to the surface or area to be heated, and also ensures that the heat produced by the apparatus is evenly distributed over its surface.

This device, in small capacity embodiments, may be delivered or transported by standard post in tubes no greater than 650mm (2 ft) long by 64mm (2l/2 inches) diameter. In such embodiments the invention may provide a heating mat that can be folded three or four times for postage in an envelope less than 10 mm thick.

The present invention may also be operated while folded and thereby be able to operate at several alternative heat outputs per unit area heated, eg low, medium or high according to whether it is operated as a single layer, or folded to give two or three thicknesses. The heating apparatus may also be provided with hinges along a line which is indented and heating element can be crinkled to reduce the possibility of fatigue in the element when repeatedly folded.

In high capacity embodiments the invention may make use of a ledge in the transformer housing for holding the transformer in position, suspending the coils off the housing floor, and also providing hand-holds for portability and stiffen the sides of the housing.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description that is given by way of example only and with reference to the accompanying drawings in which : Figure 1 illustrates a plan view of a heating element of the apparatus as configured in one embodiment of the present invention, Figure 2 illustrates the elements and procedures involved in forming a cover around a heating element to form the heating apparatus in another embodiment, and Figure 3 shows a heating element as configured in yet another embodiment of the present invention.

Figures 4 and 5 show a double wound iron core transformer configured for use with the present invention in one embodiment.

Figure 6 shows the elements and procedures involved in combining the heating element and the cover to form the heating apparatus according to one aspect of the present invention, and Figure 7. 7A show possible configurations of the ends of the heating wires.

Figure 8 shows an embodiment of the present invention allowing for different heating levels, and Figures 9. 9A show etched versions of the heating element.

Figure 10 shows a low capacity heating apparatus complete with electrical components and a transformer within a power supply lead.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 illustrates a plan view of the heating apparatus as configured in one embodiment of the present invention.

The heating apparatus 1 is formed from a single heating element 2 placed in and enclosed by a cover 3.

Brazed to separate ends of the heating element 2 are two connection terminals, shown in this embodiment as connection leads 4. The connection leads 4 may also be connected into an electrical energy supply (not shown).

As can be seen from Figure 1 the heating element 2 is constructed from a metallic mesh as disclosed in PCT Patent Application No. PCT/NZ95/00108.

Figure 2 shows a method of constructing the heating apparatus in accordance with another aspect of the present invention.

In such an embodiment a roll of conductive mesh 5 is fed out so that a flat length of heating element 6 is formed. The heating element 6 includes connection terminals 7 that lie out to the side away from the heating element 6. The heating element 6 may then be pressed flat and cut to the required length for the heating apparatus to be formed.

In a separate location a roll of non-conductive mesh 8 may be rolled out onto a support table 9 and the heating element 6 previously formed may be laid on top of the non- conductive mesh played out from the roll 8. A roller 11 may pull the non-conductive mesh 8 forwards and also apply a top layer 12 onto the heating element 6.

The top layer 12 may be formed from a material that readily conducts heat energy such as rubber. Lastly the mesh 8 and top layer 12 which sandwich the heating element 6 are then heat sealed together to form an enclosing cover.

With reference to the method shown in Figure 2, if the element 2 is constructed from a material that is capable of being gripped by a magnet, the element may be held in place using a magnetic force while the layers of the cover are moved into position.

Figure 3 shows a heating element constructed in accordance with another embodiment of the present invention.

The heating element 1 is formed from a thin sheet of conductive material such as stainless steel to form a 40mm wide by 0. 25mm deep electrical circuit 50m long.

Alternatively the mesh as shown in Figure 1 may be used. The heating element has attached at either end a connection terminal, shown in this embodiment as leads 2. The heating element 1 is positioned on top of a backing material 14. The edges of this backing material may also be weighted to ensure that the heating apparatus, when fully formed can lie out in a substantially flat shape when in use.

The heating element 1 also includes a number of apertures or holes 15. These holes are used to ensure that the backing material 14 bonds strongly with the top cover of the apparatus formed. The holes 15 allow direct contact between the upper and lower surfaces of the device's cover (not shown) and are especially important when the bonds between each surface of the cover and the heating element are weak.

Figures 4 and 5 show a transformer configured for use with the present invention in one embodiment. The transformer includes a splash proof lid 16, which overlaps a housing 17. A ventilation gap 18 is provided between the lid 16 and the housing 17.

Additional vents 19 are also located in the housing 17 to allow hot air to escape from the housing, and cool air to enter. The housing 17 also includes a ledge 20 to which a transformer iron may be seated. The ledge 20 allows the transformer to be easily transported. The ledge 20 ensures that the transformer iron is held near the centre of the housing 17 and that the coils of the transformer are held off the bottom of the housing 17. The ledge 20 also securely fits the transformer into the housing 17, ensuring that it does not rattle or move around during transportation. Holding the transformer off the bottom of the housing 17 also ensures that any water that splashes through the vents 19 is not placed in contact with the transformer coils.

Figure 5 shows the internal configurations of the transformers components. An input wire 21 is attached to the primary side 24 of the transformer via a current sensitive fuse 22 and a heat sensitive fuse 23. As can be seen from Figure 5 the heat sensitive fuse 23 is located near the top of the transformer housing, being the hottest part of the transformer.

Output leads 25 lead from the secondary side of the transformer are connected via a bolt joint to the heating apparatus (not shown) supply leads 26. As can be seen from Figure 5 the connection between leads 25 and 26 is made via a bolt to ensure secure and permanent connection between these two elements.

In some instances, temporary connections may be provided via plugs or sockets. If these connections are weak or intermittent the surrounding area may be heated substantially by the electrical current transferred. A heat sensitive fuse in the transformer housing (not shown) will fail if the heat is dangerously high, maintaining the safety of the device.

With reference to Figure 6 there is shown a diagrammatic representation of one method of forming the present invention by general arrow 60.

A length of heating element 63 is drawn between alternating pulleys 61 and 62. The gap between adjacent pulleys is increased which produces a zig zag effect. The wires are drawn over one side of a cover 64 and a further side (not shown) is placed on top of the wires and the cover is heat fused together. Bending lines 65 are configured so that the end device is able to be folded and transportable. The length of heating element that crosses the bending lines is angled which reduces the wear on the heating element when the present invention is folded.

With reference to Figure 7 and 7A, there are shown ends of the heating elements that form connections to an energy supply. These are shown by arrow 70.

With reference to Figure 7, the wire 73 extending from the heating apparatus 1 is connected to a connection means 72 via a mass of metal that is oblong in shape.

With reference to Figure 7A, the mass is shown by arrow 75 and is substantially spherical.

The advantage of adding a mass of metal, is that any heat produced by faulty connection or some other means may be dissipated avoiding a breakdown of the connection.

With reference to Figure 8, there is shown a heating apparatus 80 in accordance with one embodiment of the present invention.

The apparatus 80 includes heating element 81 and second heating element 82. Heating element 81 is connected to terminal 83. Heating element 82 is connected to terminal 84. The heating elements 81 and 82 are connected at point 85. The point 85 is connected to terminal 86.

The embodiment 80 allows three different heating output levels to be achieved depending on the terminal combination that is connected to the power source (not shown).

For example if terminals 83 and 84 are connected to the power source, then the higher resistance provided by the combined length of the heating elements 81 and 82 as a result of the combination of both of the lengths of heating elements 81 and 82, will result in the lowest heating level output.

Alternatively, if terminals 83 and 86 are connected to the power source, a high heating output would be achieved, as the length of heating element will be defined by the length of heating element 81 only, which is the shortest.

Alternatively, if terminals 84 and 86 are connected to the power source, a medium heating output will be achieved, as the resistance will be determined by the length of heating element 82 only.

In this way, a simple and yet effective method of achieving a range of heating outputs is provided.

With reference to Figure 9A there is shown a heating element 90 in accordance with one aspect of the present invention.

The heating element is formed by placing an aluminium foil onto a non-conducting surface such as polyethylene or PVC, and etching the heating circuit into the foil. In this way, a simple and cost effective way of manufacturing the heating element for the present invention is provided. The terminals 91 and 92 may be connected to a power source. Terminals 91 and 92 are ideally shaped for a battery charger connection.

With reference to Figure 9B, there is shown a heating element 93 formed in substantially the same way as that shown in Figure 9A.

The heating element 93 has a first circuit 94 etched into it and a second circuit 95 etched into the foil. This provides two heating element lengths. Consequently, the heating element shown in Figure 9B has the capability of various heating output levels being chosen, depending on the connection to the power source of the terminals 96,96A, 97 and 97A ; in a similar fashion to that provided for in the description of Figure 8. By way of explanation only, for the lowest resistance, the terminals 97 and 97A will be both connected to the same end of the power source and terminals 96 and 96A will both be connected to the other terminal on the power source. This may provide the least resistance depending on the etching dimensions, and hence the highest heat output on the heating element.

A low heat output may be provided when terminals 97A and 96A are arced between the power source as this provides a length of most resistance.

A medium heating output may be provided by connecting the power source between terminals 97 and 96 only.

Of course, the dimensions of the etchings will determine what configuration will result in the particular heating output, and the above description is given by example only to illustrate the inventive principle.

Figure 10 shows a low capacity heating apparatus 100 complete with electrical componentry and a transformer within a power supply lead.

Figure 10 shows a heating element as a dotted outline 101. The heating element is connected to two separate connection terminals, shown as connection leads 104. The connection leads are provided as part of a power supply cord 105. The connection leads 104 may be connected to a transformer 107.

The free end 106 of the power supply lead 105 includes a socket 108 which may be connected to any standard AC mains power distribution network. Next connected into the supply lead 105 is an electrical transformer 107 and a dimmer switch 108, both within a fire resistant housing. The transformer 107 is then connected in turn to the connection terminals 104 and hence the heating element 101.

Also incorporated into the heating element end of the power supply lead 105 is a heat sensitive fuse (not fully shown). This fuse will disable the supply of power to the heating element 101 if the temperature within the supply cord 105 exceeds a predetermined maximum level. In some embodiments the electric transformer 107 may also include heat and current sensitive fuses and/or switches as well.

The dimmer switch 108 is provided to allow the user to regulate a supply of power to the heating element 101 and hence the amount of heat generated by same. The user may simply operate this dimmer switch to control either the voltage or current of the electrical energy supplied to the hearing element 101.

It should be appreciated that the heating element 101 can be a single wire, or constructed from a metallic mesh, similar to that disclosed in PCT Patent Application No. PCT/NZ95/00108.

It should also be appreciated that the heater depicted in Figure 10 can be any shape and in particular it could be long and narrow as may be required to warm pot plants around the perimeter of a conservatory. For example, the heating apparatus could have a surface area ranging from 0. 5m' to 3m'if required. In this case the portable heater may be only two or four wires across in width, having an elongated structure that can be easily rolled up.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.