GB2206750A

GB2206750A - Battery powered microwave cooking apparatus

Info

Publication number: GB2206750A
Application number: GB08713832A
Authority: GB
Inventors: James Douglas Haslam
Original assignee: POWAMATE Ltd
Current assignee: POWAMATE Ltd
Priority date: 1987-06-12
Filing date: 1987-06-12
Publication date: 1989-01-11
Also published as: GB8713832D0

Abstract

The apparatus comprises a microwave cooker (4) which is adapted to operate on mains electricity, and an inverter 6 which is mechanically connected to the microwave cooker to form a single cooking unit and which is for enabling the microwave cooker to operate on at least one battery. The inverter 6 may comprise MOSFETS (16), (18), (Fig. 2), and a plurality of parallel- connected toroidal power transformers (10), (12), (14) whereby the inverter has a low profile. A conventional mains plug is retained on the cooker to enable it to operate on a normal mains supply when available, the inverter having a socket (24) is receive the plug. A switch 20 allows the inverter output to be connected alternatively to a second socket 22 which can be used to operate televisions, lights, power tools, refrigerators, computers etc. The apparatus may be used on vehicles, such or coaches and boats, and in order to provide protection against voltage spikes on the battery supply in such vehicles, high power zener diodes may be provided in association with a heating element of a circuit breaker. The cooker 4 and inverter 6 may be screwed together, allowing the cooker 4 to be separated for normal use in the home. <IMAGE>

Description

MICROWAVE COOKING APPARATUS This invention relates to microwave cooking apparatus and it relates more especially to battery powered microwave cooking apparatus.

Mains operated microwave cooking apparatus is well known and such cooking apparatus is increasingly being used in the home. The microwave cooking apparatus is able to cook or reheat many things faster than using a conventional oven and thus the microwave cooking apparatus is quickly becoming a preferred if not essential piece of equipment in the home. When persons go on holiday or for long or short trips, self catering is often involved if the persons are staying in a boat, a caravan or a purposebuilt camping vehicle. It is usually not then possible to use a microwave cooker and so the persons are forced to change their preferred mode of cooking and to use other cooking apparatus. In addition, there are other situations such as at outdoor exhibitions or at remote construction sites where the lack of availability of a microwave cooker presents a problem.

It is an aim of the present invention to obviate or reduce the above mentioned problems.

Accordingly, this invention provides battery powered microwave cooking apparatus, which apparatus comprises a microwave cooker which is adapted to operate on mains electricity, and inverter means which is mechanically connected to the microwave cooker to form a single cooking unit and which is for enabling the microwave cooker to operate on at least one battery.

Since the battery powered microwave cooking apparatus forms a single cooking unit, it is of a neat appearance and it can easily be moved from place to place, should this be required. The microwave cooking apparatus can be constructed to be of quite a small size so as not to increase substantially on the overall size of known microwave cookers.

Usually, the microwave cooker will be positioned on top of the inverter means.

Preferably, the inverter means is of substantially the same length and width as the length and width of the microwave cooker. Also preferably, the inverter means is substantially i to i the height of the microwave cooker.

Preferably, the microwave cooker is separable from the inverter means so that the microwave cooker can be used as a normal microwave cooker in a separated mode from the inverter means in premises provided with mains electricity.

This facility is based upon the realisation that it makes no sense to have a microwave cooker sat on a boat, in a caravan or the like all week, only to be used occassionally at weekends. For such weekend use, it would be advantageous to be able to use the same microwave cooker that is normally used in the home and this facility is afforded by the embodiment of the present invention in which the microwave cooker is separable from the inverter means. Thus, after use on a holiday or other period away from the home, the microwave cooker can be separated from the inverter means and taken back to the home for normal use. This avoids the need to have two microwave cookers.

The microwave cooker may be connected to the inverter means by screw means which merely need to be undone in order to enable the microwave cooker to be separated from the inverter means. Usually, the screw means will be a plurality of screws but wing nuts or screw clamps may also be employed.

Preferably, the inverter means includes first power take off means which is for enabling the inverter to operate, from the battery1 mains operated devices which are connected to the first power take off means. Usually, the first power take off means will be a socket so that the mains operated devices can be plugged into the socket.

The first power take off means may advantageously be used for running televisions, lights, power tools, toasters, sandwich makers, boilers, hair dryers, refridgerators, kettles and computers. Generally, all normal domestic and industrial equipment that is normally operated by mains electricity can be operated using the first power take off means.

The apparatus of the invention may include second power take off means which is in the form of a socket and which is for enabling a plug on the microwave cooker to be plugged into the inverter means, the plug on the microwave cooker then always being available for enabling mains operation of the microwave cooker. The facility of leaving the plug on the microwave cooker is especially convenient once the microwave cooker has been separated from the inverter means, because then there is nothing further to do in order to work the microwave cooker in its usual manner in the home. It is just necessary to plug the microwave cooker into the mains electricity in the home, switch on and the microwave cooker will then be operating in its normal mode of use.

The first power take off means may be positioned at the front of the apparatus, and the second power take off means may be positioned at the rear of the apparatus.

The apparatus may include a change over switch for placing the first or the second power take off means in circuit. Where a power change over switch is employed, this is preferably positioned at the front of the apparatus.

The inverter means may comprise at least two transformers connected and arranged for parallel operation.

In one embodiment of the invention, there are three transformers, and the inverter means is then arranged to operate on 24 volts battery power. Preferably, the three transformers are three 500 watt transformers.

In another embodiment of the invention, there are two transformers and the inverter means then operates on 12 volts battery power.

Advantageously, the transformers are toroidal transformers. The use of the toroidal transformers enables a very low profile to be achieved which facilitates the formation of the apparatus into a very small and compact size. The small and compact size could not be achieved using an E- or an I- core transformer which would be of the order of twice the size and three times the weight.

Preferably, the inverter means includes mosfet transistors which have a large capacity and a low resistance in the on state, the mosfet transistors being effective to reduce on power dissipation. Preferably, the mosfet transistors are block mosfet transistors.

The inverter means advantageously includes an input circuit breaker and Zener diodes connected directly across the input circuit breaker, there being a circuit breaker heating element which is employed to drop the voltage across the input circuit breaker when the Zener diodes operate.

Usually, the apparatus of the invention will be powered by more than one battery, for example two or three batteries.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings: Figure 1 is a perspective view from the front and above of battery powered microwave cooking apparatus; Figure 2 shows a first circuit in which the battery powered microwave cooking apparatus operates on a 24 volt battery supply; and Figure 3 shows a circuit in which the battery powered microwave cooking apparatus operates on a 12 volt supply.

Referring to Figure 1, there is shown battery powered microwave cooking apparatus 2 comprising a microwave cooker 4 and inverter means 6. The microwave cooker 4 shown in the drawings is a standard microwave cooker manufactured by Philips and it is adapted to operate on mains electricity.

The inverter means 6 is mechanically connected to the microwave cooker 4 by four screws (not shown). When the inverter means 6 is mechanically connected to the microwave cooker 4, a single cooking unit is formed.

The inverter means 6 is for enabling the microwave cooker 4 to operate on at least one battery as will be described in detail hereinbelow.

Referring more especially to Figure 2, it will be seen that the circuit of the inverter means includes a 24 volts nominal dc supply 8 and three transformers 10,12,14.

The transformers 10,12,14 are toroidal transformers and they are connected in parallel as shown. Two semi conductor power devices 16,18 are connected across the transformers 10,12,14. The circuit includes å change over switch 20 for bringing into operation either a first power take off socket 22 for mains operated apparatus such for example as toasters, televisions, kettles and the like, and a second power take off socket 24 for receiving a plug (not shown) which is connected to the microwave cooker 4.

The inverter means 6 is very small and compact as can be seen from Figure 1. More specifically, the inverter means 6 is of substantially the same length and width as the length and width of the microwave cooker 4. Also, the inverter means 6 is substantially only i to 5 of the height of the microwave cooker. The inverter means 6 thus has a very low profile and it also has a high power handling capacity, with a very small bulk of iron. The illustrated inverter has a power rating of 50Hz. The small size of the inverter means 6 is mainly allowed by using the three transformers 10,12,14 which are 500 watt transformers. A single 1500 watt transformer could not in fact be made as a toroidal transformer with a 24 volt DC input.This is due to the physical constraint of the copper wire that would be required to wind the low voltage winding, this being too large to be wound by normal toroidal manufacturing processes.

The connection of the three transformers 10,12,14 in parallel overcomes this problem whilst enabling the inverter means to be very small in size and weight.

The inverter means 6 is very efficient over the whole range of operating conditions from no load to full load. By using block mosfet transistors in addition to the toroidal transformers 10,12,14, very low standing current and power dissipation is achieved. This means that no forced cooling or special venting is necessary. This is very desirable as a practical matter. More specifically, as the apparatus is designed to be used on various types of vehicles, for example coaches, lorries, boats, military vehicles, camping vehicles and caravans, forced cooling or special ventilation could cause problems with dust or foreign bodies being sucked in, moisture ingress and general unwanted material inside the apparatus 2.This problem does not occur with the apparatus 2 of the present invention since all the cooling necessary is achieved by the outer case of the inverter means 6 using natural convection. The inverter means 6 has been designed to prevent heat being generated and losses are kept to a minimum using mosfet transistors of very large capacity with a very low on resistance, thereby cutting down power dissipation to a minimum. The transformers 10,12,14 are themselves extremely efficient with very little copper and iron loss. The low iron loss is achieved by using the toroidal design as opposed to an E- or an I- core transformer which would in fact be twice the size and three times the weight.

The inverter means 6 has also been designed on the assumption that users will from time to time plug virtually anything into the apparatus 2, irrespective of power rating or instructions. The inverter means 6 thus includes plenty of over capacity on its most vulnerable components, that is the output transistors. For example, on full load, the apparatus 2 will take approximately 60 amps from a nominal 24 volt system. The power devices employed will handle 145 amps continuously and 500 amps intermitently. This gives plenty of time for protection circuits to operate without damage, but allowing such things as induction motors with very high start up current to run without nuisance tripping.

The change over switch 20 shown in Figure 2 is also shown in Figure 1, and as will be seen from Figure 1, the change over switch 20 is positioned at the front of the apparatus 2. When the microwave cooker 4 is not in use, the change over switch 20 can be operated to enable the full power of the inverter, that is 1500 watts, to be available for general use. This is a very useful feature allowing most common industrial and domestic electrical equipment to be operated with its running and start up capacity of 1500 watt continuous and 2500 watt start up capacity at standard main voltages of 110 - 120V at 60 Hz and 220 - 240viz at 50 Hz. Items such for example as televisions, Hi-fi equipment, refridgerators, water pumps, power tools etc can thus be plugged into the first power take off socket 22, this socket 22 also being shown in Figure 1.

The compact size of the apparatus 2 is especially useful for fitting into vehicles where space is at a premium, and this is specially often occurs on coaches and boats.

It is to be mentioned that operating electrical equipment on vehicles often proves to be difficult. For example, on long distance coaches, the electrical system is often extremely overworked and it is subject to very considerable voltage spikes and fluctuations in supply voltages. This is due to the amount of electrical equipment now being used on coaches being far greater than it used to be. This results in a standard alternator of, for example, 90 amps - 120 amps maximum output struggling to maintain voltage. There is also a particularly demanding braking system in common use called a Telemar Retardar, which is in fact a form of dynamic braking system. When this system is operated by the vehicle driver depressing the brake pedal, the braking system draws a very considerable current of 200 amps from the supply. This results in the alternator regulator turning itself fully up to try and compensate for the voltage drop in the system. As this happens, the driver then usually takes his or her foot off the brake, taking away the 200 amp load. For a fraction of a second, the alternator regulator is still turned fully up but the load has disappeared and this causes the voltage to rise drastically giving a very large voltage spike. Such a large voltage spike can be fatal to any types of electrical equipment, especially those having a power rating of the type to which the present apparatus 2 applies. In order to combat this possible problem, the inverter means 6 includes very large power handling Zener diodes having an instantaneous rating of 9.5 Kw.These Zener diodes are placed directly after an input circuit breaker, as close as possible using a circuit breaker heating element to drop the voltage across the input circuitbreakerwhen the Zener diodes operate.

When the apparatus 2 is to be used on boats, obviously batteries and battery charging become a point of considerable importance. Indeed, most boat owners are constantly concerned about their batteries being flattened, S the recharging of batteries on some boats appears to be a very involved process. The apparatus 2 has been constructed with a view to conserving battery power and giving maximum electrical efficiency. Furthermore, when boats are in ports or marinas, shore power is usually available and it makes sense to use this power rather than to use batteries. Some boats have mains generators installed and these have to be run to perform certain function aboard so it is again desirable to use the mains as may be available rather than batteries.In order to accommodate such possibilities, the microwave apparatus 2 is left as a totally standard unit which even has its normal plug left on it. This plug is normally put into the second power output socket 24 which is shown in Figure 2 and which is in fact present at the back of the apparatus 2 as shown in Figure 1. When mains electricity is available, the plug can simply be removed from the socket 24 and plugged into shore power or mains boat power.

Especially for boats and tents which are often only used intermitently at weekends, the apparatus 2 as shown in Figure 1 is constructed such that the microwave cooker 4 can be separated by the inverter means 6 merely by undoing four screws (not shown) as mentioned above. Thus the microwave cooker 4 can normally be used in the home and it can easily be connected to the inverter means 6 when it is desired to be used on a boat or the like. Indeed, the inverter means 6 can be left on the boat or the like if desired. Modifications to the microwave cooker 4 in order to connect it to the inverter means 6 are not required, so that inconvenience to a user is reduced to the absolute minimum.

The apparatus 2 is thus able to give the speed and convenience of microwave cooking, together with the convenience of being able to take a supply from either 220/240 volts AC or 24 volts nominal DC via the inverter means 6.

At the flick of the change over switch 20, an output of up to 1500 watts at 220/240 AC is available from the inverter when the microwave cooker 4 is not in use, in order to run all normal domestic and industrial equipment as mentioned above and including toasters, sandwich makers, boilers, hair dryers, refridgerators, and computers. The apparatus 2 is constructed to be robust and the body of the inverter means 6 is made of 3mm thick aluminium. The inverter means 6 is thus able to withstand use on vehicles. The body also acts as a heat sink for the electrical components and this helps to dissipate the small amount of heat generated by the electrical components of the inverter means 6. The apparatus 2 is especially sparing of power in batteries.

Referring now to Figure 3, similar parts as in Figure 2 have been given the same reference numerals and their precise construction and operation will not again be given. It will be seen that in Figure 3, only two of the transformers 10J2 are employed. The circuit shown in Figure 3 operates on 12 volt battery power.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, more transformers may be employed in the circuit shown in Figures 2 and 3. Also, another type of microwave cooker 4 to the one shown in Figure 1 may be employed. Further, one, two or- more batteries as may be desired may be utilised.

Claims

1. Battery powered microwave cooking apparatus, which apparatus comprises a microwave cooker which is adapted to operate on mains electricity, and inverter means which is mechanically connected to the microwave cooker to form a single cooking unit and which is for enabling the microwave cooker to operate on at least one battery.

2. Battery powered microwave cooking apparatus according to claim 1 in which the microwave cooker is positioned on top of the inverter means.

3. Battery powered microwave cooking apparatus according to claim 1 or claim 2 in which the inverter means is of substantially the same length and width as the length and width of the microwave cooker.

4. Battery powered microwave cooking apparatus according to any one of the preceding claims in which the inverter means is substantially one quarter to one third the height of the microwave cooker.

5. Battery powered microwave cooking apparatus according to any one of the preceding claims in which the microwave cooker is separable from the inverter means so that the microwave cooker can be used as a normal microwave cooker in a separated mode from the inverter means in premises provided with mains electricity.

6. Battery powered microwave cooking apparatus according to claim 5 in which the microwave cooker is connected to the inverter means by screw means which merely need to be undone in order to enable the microwave cooker to be separated from the inverter means.

7. Battery powered microwave cooking apparatus according to any one of the preceding claims and including first power take off means which is for enabling the inverter to operate, from the battery, mains operated devices which are connected to the first power take off means.

8. Battery powered microwave cooking apparatus according to claim 7 and including second power take off means which is in the form of a socket and which is for enabling a plug on the microwave cooker to be plugged into the inverter means, the plug on the microwave cooker then always being available for enabling mains operation of the microwave cooker.

9. Battery powered microwave cooking apparatus according to claim 8 in which the first power take off means is positioned at the front of the apparatus, and in which the second power take off means is positioned at the rear of the apparatus.

10. Battery powered microwave cooking apparatus according to any one of claims 7 to 9 and including a change over switch for placing the first or the second power take off means in circuit.

11. Battery powered microwave cooking apparatus according to any one of the preceding claims in which the inverter means comprises at least two transformers connected and arranged for parallel operation.

12. Battery powered microwave cooking apparatus according to claim 11 in which the transformers are toroidal transformers.

13. Battery powered microwave cooking apparatus according to any one of the preceding claims in which the inverter means includesmosfet transistors which have a large capacity and a low resistance in the on state, the-mosfet transistors being effective to reduce on power dissipation.

14. Battery powered microwave cooking apparatus according to any one of the preceding claims in which the inverter means includes an input circuit breaker and Zener diodes connected directly across the input circuit breaker, there being a circuit breaker heating element which is employed to drop the voltage across the input circuit breaker when the Zener diodes operate.

15. Battery powered microwave cooking apparatus substantially as herein described with reference to the accompanying drawings.