GB2219154A - Portable engine-driven welder - Google Patents

Abstract

The welder comprises an internal combustion engine driving an alternator which produces a first AD output 12 at 240v AC and feeds a transformer primary winding which is tapped to give a second AD output 16 at 110v AD, the secondary winding of the transformer providing a third AD output 18 for welding. The alternator field 22 is excited through a capacitor 24 under no load conditions and through a current transformer 26 under load. A potentiometer 28 connected to the secondary of the current transformer 26 can be adjusted to vary the effective turns ratio of transformer 26 and thus adjust the welding current available from the output 18. <IMAGE>

Description

Title Engine Driven Welder This invention relates to an engine driven welder which comprises an internal combustion engine driving an alternator for producing an electrical output fpr welding purposes.

Background to the Invention Known engine driven welders have two AC outputs in addition to the output for welding. These AC outputs are produced from the secondary of a transformer the two halves of the winding of which are connected in series to give one output and in parallel to give another output.

Hence, the two outputs cannot be used simultaneously. The invention aims to provide an engine driven welder in which the two outputs (which are additional to the output for welding) are available for simultaneous use.

Summary of the Invention According to the invention a portable engine driven welder comprises an internal combustion engine, and an alternator driven by the internal combustion engine, the alternator producing a first AC output and feeding the primary winding of a transformer tapped to give a second AC output, the secondary winding of the transformer providing a third AC output for welding.

The tapping of the primary winding giving the second AC output is preferably centre tapped to earth, e.g. to give 55-0-55v AC to supplement the first AC output which may be at 240v AC.

In a preferred embodiment the alternator has a field excited through a capacitor under no load conditions, and through a current transformer and bridge rectifier under load. The current transformer preferably has a variable ratio, under the adjustment of a manually contrpllable knob, to vary the welding current. The current transformer may have a primary winding connected to the alternator and a secondary winding connected to the bridge rectifier via a potentiometer which varies the ratio of the current transformer, the output of the rectifier bridge supplying a DC current to the alternator field.

A portable engine driven welder according to the invention will now be described by way of example with reference to the accompanying drawing which shows the electrical circuit diagram of the welder.

The welder has an internal combustion engine, such as a petrol or diesel engine, which drives an alternator. The alternator output, at 240v AC 50Hz, is taken from slip rings 10. The alternator output provides a first AC output 12, also at 240v AC.

The alternator feeds the primary winding of a transformer 14 a part of the winding of which is centre tapped to earth to provide a second AC output 16 at llOv (55-0-55v) 50Hz. The secondary winding of the transformer produces an output 18 at 60v AC for welding purposes. A choke 20 is included in the secondary circuit for stability purposes.

The alternator field 22 is excited through a capacitor 24 under no load conditions and through a current transformer 26 under load. The secondary winding of the current transformer is tapped and connected to a potentiometer 28 adjustable by means of a control knob which alters the welding current available from the welding output 18. The secondary of the current transformer 26 is connected to a full wave rectifying bridge circuit 30 which produces a DC current for exciting the alternator field 22.

A welder will choose the required welding current before starting work by adjusting the knob to set potentiometer 28 which has the effect of varying the ratio of the current transformer 26.

In addition to the welding output 18, the welder has the two outputs 12 and 16 which can be used simultaneously if required.

Claims (7)

Claims

1. A portable engine driven welder comprising an internal combustion engine, and an alternator driven by the internal combustion engine, the alternator producing a first AC output and feeding the primary winding of a transformer tapped to give a second AC output, the secondary winding of the transformer providing a third AC output for welding.

2. A portable engine driven welder according to claim 1, wherein the tapping of the primary winding giving the second AC output is centre tapped to earth.

3. A portable engine driven welder according to claim 1 or 2, wherein the second AC output is at 110v AC and supplements the first AC output which is at 240v AC.

4. A portable engine driven welder according to any of the preceding claims,. wherein the alternator has a field excited through a capacitor under no load conditions, and through a current transformer and bridge rectifier under load.

5. A portable engine driven welder according to claim 4, wherein the current transformer has a variable ratio, under the adjustment of a manually controllable knob, to vary the welding current available from the third AC output.

6. A portable engine driven welder according to claim 4 or 5, wherein the current transformer has a primary winding connected to the alternator and a secondary winding connected to the bridge rectifier via a potentiometer which varies the ratio of the current transformer, the output of the rectifier bridge supplying a DC current to the alternator field.

7. A portable engine driven welder substantially as herein particularly described with reference to the accompanying drawings.