Some pointers
Series welders are used by manufacturers of sheetmetal doors, automobiles and consumer products such as
barbecue grills and lawn mowers. The process joins sheet as thick as 16 gauge, 0.059 inch. Direct welding
machines join work of any suitable thickness with a properly sized transformer.
Using series-type multiple-gun machines, designers should space welds at least 2 inches apart to minimize shunt
losses-current wander from the spot-weld location. High shunt-current loss requires larger KVA rated transformers
with greater weld-current output to supply sufficient current to the welds.
To assure that all series welds in the circuit are of equal size and strength, the electrical secondary circuit-current
path from the transformer secondary through both electrodes and the workpiece-must be balanced. The machine
manufacturer will balance secondary circuits by selecting cables of specific lengths. Users should assure that
electrodes, cables, and connections are kept secure and clean.
Keep electrodes properly and similarly shaped. This rule is clear when we consider a machine making four spot
welds simultaneously using one transformer and electrodes of 1/4 inch diameter face. If the faces mushroom to
5/16 inch, the welds require 55 percent more current; 3/8 inch, 125 percent more.