Please note that all information provided at and by Hobby Spot is to be used at your own risk.  Hobby Spot has made tremendous efforts to insure the accuracy of this information but all risks, responsibilities etc for the use and accuracy of this information lies exclusively with the end user.

The figure at left shows a very simplified transformer based resistance welder.  AC voltage is transformed between two voltages while overall power remains constant.  Typical home built spot welders may use a control transformer to step down voltages and provide large currents while industrial transformers use higher power equipment allowing a step-up in voltage to provide very high welding current.

A simple capacitive welder is shown at right.  A DC power supply is used to store charge in a large capacitor.  The capacitor is then discharged via a relay into the work piece.  The power stored in a capacitive welder is one half the voltage squared multiplied by the capacitance (1/2V^2*(C) ).  Capacitive welders provide large and short current pulses.  This is advantageous to the initial melting of weld metal (which happens in the first few mili-seconds) and to manageable power input (a 110 VAC wall transformer can be used).

Resistance welding called spot welding joins two pieces of metal using electrical power.  Electrodes clamp the work piece together and a large current is passed thought the electrodes into the sheets of metal.  The current heats and melts the metal.  What is left is a small “spot” were the metal has been jointed or “welded” together.

Factors such as electrode cooling of the metal surfaces, weld time, electrode current and clamping pressure effect weld quality.  You may need to experiment with all of these parameters to determine the best weld for your application.  Cooling happens as weld electrodes remove heat from the metal surface.  Heat is also conducted away from the weld location via conduction.  Peek electrode current is critical to resistance welding.  The weld nugget starts to forms in the first few mili-seconds of the discharge.  Electrode clamping pressure insures good contact between metal surfaces.  Electrodes should not be used as a press, but clamping pressure acts to smooth out surfaces roughness on the micro-scale.

If weld current pulses are large and quick, heat conduction to the electrodes and away in the metal itself is not significant.  In this case the metal may be melted as show in the figure right.  With thin sheet metal this may be unavoidable.  However, care should be taken to avoid excessive over current as molten metal may “explode” out of the weld location leaving a “large” hole. 

Some applications may not allow for an electrode on each side of the work piece.  In these situations  two electrodes may be placed on the same side in parallel.  Current flows into the metal though the first electrode creating a weld nugget and then into the second electrode creating the second.  Parameters such as electrode pressure and weld current are also critical in this configuration.  Uneven or inadequate pressure can damage electrodes and leave holes in the work piece.

Welding can also be made with a single electrode, such as a welding pen, when the other electrode is farther away.  In the figure shown an alligator clip is attached to the bottom work piece some distance from the weld to be made.  The welding pen is then used to create a spot at the desired location.  This system works better for welding thinner material.  Placing the clip as close as possible to the weld is also importance for avoiding excessive losses in power.  Pen pressure and current still play an important role.

Please note that all information provided at and by Hobby Spot is to be used at your own risk.  Hobby Spot has made tremendous efforts to insure the accuracy of this information but all risks, responsibilities etc for the use and accuracy of this information lies exclusively with the end user.