Capacitive Discharge (CD) Welders
The stored energy welding power supply - commonly called a Capacitive Discharge Welder or CD Welder - extracts energy from the power line over a period of time and stores it in welding capacitors. Thus, the effective weld energy is independent of line voltage fluctuations. This stored energy is rapidly discharged through a pulse transformer producing a flow of electrical current through the welding head and workpieces.
Capacitive discharge power supplies are rated in accordance with the amount of energy they store and the welding speed. The energy stored, expressed in watt-seconds (joules), is the product of one-half the capacitance of the capacitor bank and the square of the applied voltage. The energy delivered to the electrodes is considerably less than this value because of losses in the primary and secondary circuits.
Some capacitive discharge power supplies provide a 'Dual Pulse' feature which allows the use of two pulses to make a weld. The first pulse is generally used to displace surface oxides and plating, and the second pulse welds the base materials. This feature also reduces spitting.
For more information regarding how to choose the right power supply for your application, read our blog: 'AC, DC, CD or HF: Which Spot Welding Power Supply Should I Use?.
And for more information about the resistance welding process read our Fundamentals of Resistance Welding.