The inventor has found that in conventional electrical generation units of the type having a generator which must be excited or energised to produce an electrical energy output, as soon as a loading is applied to the output the electrical energy output drops. This problem is particularly acute in portable welding machines where the loading during welding is of such a nature that it can virtually shutdown the generator unless its drive means is substantially oversized.

According to a first aspect of the invention there is provided an electrical power generation unit including -drive means for driving a drive shaft driveable by the drive means; -a first electrical generator which is connectable to the drive shaft; -a second electrical generator which is connectable to the drive shaft; and -the first generator being electrically connectable to the second generator such that, in use, substantially all the electrical energy generated by the first generator is used to excite or energise field coils of the second generator to permit electromechanical feedback regulation of the output current from the second generator to smooth out fluctuations in the output energy delivered by the second generator under a loading condition.

The first electrical generator may be a permanent magnet DC generator. The DC generator may be the DC motor of a vehicle cooling system fan, such as that provided on a Volkswagen (TM) utility vehicle.

Typically, the DC generator is mounted on a free end of the drive shaft.

However, it may be mounted in any position and be driven by a belt and pulley system driven by the drive shaft.

The second electrical generator may be an AC alternator having field coils.

Typically, the AC alternator is a standard 3-phase vehicle alternator.

The second generator may be connectable to the drive shaft by a belt and pulley system. The diameter of the pulley on the drive shaft may be selected so that, together with the operating characteristics of the primary and secondary generators, a desired output current at a specified voltage is provided from the secondary generator.

The electrical power generation unit may include a voltage regulator circuit connectable to a transformer on the output of the second generator for regulating the output voltage of the transformer at a predetermined voltage. Typically, the regulated output voltage is 220 V DC.

The electrical power generation unit may include a voltage rectifier circuit for rectifying the output voltage. The voltage rectifier may have a heat sink connectable in heat flow communication with the second generator for heat dissipation through a cooling system of the second generator. Typically the second generator cooling system includes a fan mounted to provide a flow of cooling air over the generator body.

The electrical power generation unit may include an output socket circuit connectable to permit electrical communication between any suitable tool and the power generation unit. Typically the output socket is a standard 3-pin type socket.

The electrical power generation unit may include a 3 phase rectifier and associated circuitry connectable to the power generation unit to form a welding unit having its own electrical power generation means. Typically, the alternator output is wired in delta configuration when used as a welding unit.

The power generation unit may include a battery charger circuit connectable to the power generation unit, for charging a battery connected to the battery charger or for boost starting an engine such as a vehicle engine when the battery usually employed for this purpose is inoperative.

The power generation unit may include a selector switch for selectively nominating between the circuits described above.

The electrical power generation unit may include a transportable mounting frame for facilitating the transportation of the unit. Typically, the mounting frame is a tubular cage having access openings for operator access to the power generation unit.

If required, the electrical power generation unit includes at least one additional secondary generator connectable to the drive shaft and the primary generator, in a similar fashion to that described above for the secondary generator, and co- operating with the other secondary generator in increasing the electrical energy output from the unit without the need for an increased size generator.

The drive means may be a fuel powered motor connectable to the drive shaft.

The motor may be a petrol or diesel engine connectable to the drive shaft. The selection of petrol or diesel being an operational decision based on the surrounding circumstances such as fuel availability. In a specific embodiment the drive means may be an electric motor.

The invention extends to a transportable welding unit including a power generation unit as described above.

The invention further extends to a method of providing a substantially stable supply of electrical energy under loading conditions including the steps of: -connecting a first generator connectably with a drive shaft of a drive means; -connecting a second generator to the drive shaft; -electrically connecting the first generator to the second generator such that, in use, substantially all the electrical energy generatable by the first generator is used to excite or energise field coils of the second generator.

The invention will now be described, by way of non-limiting example with reference to the accompanying diagrammatic drawings.

In the drawings, Figure 1 shows, a pictorial three dimensional view, of a portable welding unit having an electrical power generation unit in accordance with the invention; Figure 2 shows a schematic representation of the electrical power generation unit; and Figure 3 shows the block diagram of the voltage regulation circuit.

In Figure 1, reference numeral 10 generally indicates a transportable welding unit, broadly in accordance with the invention. The welding unit 10 has a mechanical drive means in the form of a petrol engine 12, an electrical power generation unit 14 operativley connected to the engine 12 and a welding unit 16, all mounted in a transportable mounting frame in the form of a cage 18.

The power generation unit 14 has a 3-pin output socket 20 for connecting of power tools (not shown), battery charger and booster terminals 22, and welder output terminals 24. A selector switch 26 is provided for selecting between the 3-pin output socket 20, the battery charger 22 and the welder terminals 24.

In Figure 2, reference numeral 14 indicates a power generation unit, broadly in accordance with the invention. The power generation unit 14 has a petrol engine 12, a drive shaft 26 driveable by the engine 12, a primary generator in the form of a permanent magnet DC generator 28 mounted on the free end 30 of the drive shaft 26, a secondary generator in the form of a standard vehicle 3-phase AC alternator 32 mounted remotely from the shaft 26 and driveable by the shaft 26 by means of a pulley system 34. The DC generator 28 output terminals 36 are connected to the AC alternator 32 field coil input terminals 38 by means of electrical cables 39, such that substantially all the electrical power generated by the generator 28 is used to excite or energise the alternator 32 field coils which in turn generates a 3-phase electrical output at output terminal 33 which is wired in a delta configuration.

The pulley system 34 comprises a first pulley wheel 40 mounted for rotation on the shaft 26, a second pulley wheel 42 mounted on the alternator 32 rotor shaft 44 and a v-belt 46 mounted over the pulley wheels 40,42 for driving the alternator rotor shaft 44 from the drive shaft 26. The diameter of the pulleys 40, 42 is selected to provide a desired output current and voltage from the alternator 32. For example, a 135 mm first pulley 40 used in combination with a standard alternator pulley for the second pulley 42 and driven by a HONDA (TM) GX or GD range engine produces a maximum open circuit voltage of 70 V. With a 5.5 HP HONDA GX 160 the output current is in the range 60-100 amperes.

In use, the engine 12 is started by a user thereby causing the drive shaft 26 to rotate at the speed of the engine 12 crank shaft (not shown). As the drive shaft rotates so the rotor of the DC generator 28 is rotated thereby generating an output current at a potential difference of 12 V across the terminals 36 at an engine 12 speed of 3600 r. p. m. The current thus generated flows along the cables 39 to the field coil input terminals 38 of the alternator 32.

The rotor shaft 44 of the alternator 32 is driven by the pulley system 34 in parallel to the generator 28, the speed of rotation being fixed by the diameter of the first and second pulleys 40,42 and the engine 12 revolutions. As a loading is applied to the output terminals 33 the alternator 32 initially exhibits a natural tendency to retard the rotation of the rotor shaft 44 and thus drive shaft 26 due to magnetisation of the field coils and rotor.

This retardation causes the engine 12 speed to drop and thus the speed of- rotation of the shaft 26 which in turn leads to a reduced voltage across the generator terminals 36. The reduced voltage at terminals 36 leads to a reduced voltage at alternator field coil input terminals 38 thereby reducing the excitation of the field coils of the alternator 32 and thus the output from the alternator at output terminals 33. This reduced output in turn reduces the retardation on the drive shaft 26 permitting the engine speed to stabilise at an operating point at which the output from terminals 33, the excitation voltage at terminals 36 and 38 are in balance.

An electromechanical feedback loop for regulating the output from the alternator at terminals 33 is thus established and will respond in a similar fashion to any subsequent changes in loading conditions.

In Figure 3, reference numeral 70 generally indicates a block diagram of a voltage regulation circuit which is provided on the portable welding unit 10. The voltage regulation circuit 70 uses an operational amplifier 72, a transistor 74, a diode 76 and a voltage divider 78. The voltage regulation circuit 70 compares the output voltage from the alternator 32 with a pre selected reference voltage and by means of the operational amplifier 72 actuates the transistor 74 to vary the output voltage from the generator 28 to a level at which the output voltage from the alternator 32 is at the desired level of the reference voltage. The Inventor believes that it is an advantage of the invention, as illustrated, that an electrical power generation unit having a true 100% duty cycle is provided without the need to substantially oversize the drive engine to provide for loading conditions. The Inventor believes that it is a further advantage of the invention, as illustrated, that a portable welding unit is provided, which has a 100% duty cycle, without being to heavy to carry, and in addition having accessories which permit a user to power power tools therefrom.