UB25 LINEAR DC RESISTANCE WELDING CONTROL
990-665
G-1
APPENDIX G
REPETITION RATES
Introduction
The term repetition rate refers to how often weld pulses can be repeated based on the Power Supplies
recharging time. The UB25 stores energy internally in a capacitor bank. This energy is used to provide
the desired weld pulses. There are limits to the duration of weld pulses the unit can provide, and time
must be provided between welds for the capacitor bank to recharge.
The graph on the next page details the maximum acceptable pulse durations at various current levels for
repetition rates of 1, 2, and 3 welds per second. The graph is divided into sections by the graphed lines.
The portion of the graph below the lines is labeled
Acceptable Durations
; the area at the top-right is
labeled
Durations Too Long
.
Weld pulses that fall below the lines in the
Acceptable Durations
section are within the capability of the
Power Supply for the stated repetition rates. The time to be used in determining the duration is the sum
of the weld period and ½ the periods of upslope and downslope, if any. For dual-pulse welding, the sum
of both pulses must be compared to the chart. This graph requires the total resistance of the secondary
circuit to be between 0.5 milliohms and 10 milliohms. Certain combinations of weld currents, durations
and repetition rates in the top-right portion of the graph may be possible. This depends upon the secondary
load and resistance. For assistance, contact the AMADA WELD TECH Applications Lab.
For welds using the current control mode, the durations can be read directly off the chart. For welds in
the voltage control or power control modes, the average current from the monitor screen and the
programmed duration can be compared to this chart.
It is possible that longer durations may be provided by the Power Supply (depending upon the details of
the secondary circuit) but the stability of the waveform may decrease. In this circumstance, a reduction
of the secondary circuit resistance and/or inductance will be beneficial. (Shorten weld cables and/or tie
them together.) Testing with the actual secondary circuit to be used will be required in this case.
