Power Supplies for Resistance Welding

Resistance Welding Equipment - Power Supplies

As with weld heads, resistance welding power supplies are available in many varieties to suit requirements based on price, control, and speed. The four basic variants are Alternative Current (AC), Capacitor Discharge (CD), High Frequency Inverter (HF), and Direct Current (DC). Their individual advantages and limitations are discussed below:

Alternating Current (AC)
As the name implies, this type of power supply sends out energy where the current changes direction every half cycle. The power supplies takes in high-voltage low-current signal from the power lines and converts switches it to a low-voltage high-current signal. In the process, the power supply does some conditioning of the AC pulse by chopping off part of the cycle and counting the number of cycles. These type of power supplies work well where a long weld pulse is required and control does not have to be very precise.
Capacitor Discharge (CD)
In these power supplies, the energy is stored in capacitor banks and delivered through a transformer to the weld head. These units work well for applications requiring short burst of energy such as for conductive materials and projection welds. However, precise control of the weld pulse shape is difficult.
Direct Current (DC)
DC power supplies take in AC energy from the power lines and convert it into DC energy for welding. Energy can be controlled to provide fixed current, voltage, or power. Peak currents are limited for such power supplies to under 6 kA.
High Frequency Inverters (DC)
Inverters are designed to mimic the signal from a DC unit but with the capability of supplying much higher current levels, up to 100 kA. Like DC units, HF inverters can be operated in current, voltage, and power mode. Some of the newer units also offer a combo mode. These units have become the workhorses in applications requiring precise control and speed (rate of welding). However, they are more expensive than AC welders at similar energy levels.