- Stored Energy (Capacitive Discharge):
- The stored energy welding power supply, commonly called a Capacitive Discharge 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 producting a flow of electrical current through the welding head and workpieces.
- Capacitive discharge power supplies are rated in accordance with the amount energy stored, expressed in watt-seconds (joules), is the product of one-haft the capacitance of the capacitor bank and the square of the applied voltage. The energy delivered to the electrodes is considerably less than this this value because of losses in the primary and secondary circuits.
- Some 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.
- Pulse Transformers - are designed to carry high secondary currents typically up to 10,000 amps. Welds made with a capacitive discharge system are generally accomplished with a single, very short weld pulse with a duration of from 1 to 16 milliseconds. This products rapid heating that is localized at the welding interface. The length of the output pulse which can normally be modified by changing taps on the pulse transformer. Polarity switching is a convenience when the machine is used to weld a wide variety of polarity sensitive dissimilar metals.
- In practical applications, the short pulse is used to weld copper and brass which require fast heating; the medium pulse is used to weld nickel, steel and other resistive materials and the long pulse is also used to weld resistive materials and the reduce sparking and electrode sticking