Spot Welder Controlled by AVR

The project utilizes a battery charger in order to create a spot welder device that is controlled by an AVR ATmega88PA.

Using a battery charger provides some benefits such as maintaining most of the power electronics parts in place. It includes heatsinks, SCR, high current bridge rectifier, and transformer. Extra precautions have to be made when putting high power AC and 5V logic circuits together which may lead to large interference noise. To feed an LDO regulator for control circuit, a capacitor, bridge regulator, and step-down transformer were used. The voltage input to the regulator was relatively free from any ripple due to the capacitor and because of the low current drawn by the microcontroller.

An ATmega88PA running at 8MHz functions as the controller which handles timing duties, zero crossing detection, and control of the SCR gate. The power and duration settings are read by the microcontroller and are displayed on the LCD along with the maximum current for the last weld cycle and the temperature of the on-chip sensor. The input to the micro to trigger a weld cycle is by using a footswitch. The current is limited by a power resistor.

Rest of the project