3
SLOPE Figure
3-3 illustrates the volt-ampere characteristics for a mig power source. The slant
from horizontal of the curve
is referred to as the ”slope” of the power source. Slope refers to the
reduction in output voltage with increasing
current. Thus, a ”constant voltage” power source with slope does not
really provide constant voltage
for reasons to be considered.
As an example
of slope, suppose the open circuit voltage is set at 25V and the welding condition
is 19V and 200
amps as shown in Figure 8-3. The voltage decreases from 25 to 19 in 200 amps;
the slope is 3V/ 100
amps. The slope
of the power source by itself, as specified by the manufacturer and measured at
its output terminals,
is not the total slope of the arc system. Anything which adds resistance to the
welding system adds
slope and increases the voltage drop at a given welding current. Power cables,
connections, loose terminals,
dirty contacts, etc., all add to the slope. Therefore, in a welding system, slope
should be measured
at the arc. Continued
on next page... Figure
3-3 – Slope Calculation of a Welding
System
