Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 68 of 72
PART 1:CALCULATION OF AVERAGE CURRENT DRAW PER WELDING TRANSFORMER
There are three classes of duty cycle to consider:
A HIGH duty cycle application is seam welding. For HIGH DUTY CYCLE applications,
the average primary current draw per transformer is:
AVERAGE CURRENT DRAW (amps) = TRANSFORMER NAMEPLATE KVA x 2
A MEDIUM duty cycle application is defined as 7 or more spot-welds in any 30-second
time interval. This corresponds to a duty cycle of more than 5%. Robot applications,
portable gun welders, or systems, which use multiple welding guns on each
transformer usually, fall into this category. For MEDIUM DUTY CYCLE applications, the
average primary current draw per transformer is:
AVERAGE CURRENT DRAW (amps) = TRANSFORMER NAMEPLATE KVA X 1.6
A LOW duty cycle application is defined as 6 or fewer spot-welds in any 30-second
time interval. This corresponds to a duty cycle of 5% or less. Manually operated
pedestal welders, welders on fixtures or hard automation welders usually fall into this
category. For LOW DUTY CYCLE applications, the average primary current draw per
transformer is:
AVERAGE CURRENT DRAW (amps) = TRANSFORMER NAMEPLATE KVA X 1.3
The result of the calculation of PART 1 determines the average current per welding
transformer. Depending on how the transformer(s) are connected to the isolation
contactor, PART 2 selects the appropriate isolation contactor rating in amperes.