©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART B 1.8.5.7
Since the 80 volts
necessary for initiating the arc
is too high for practical
welding, some means must be
used to lower this voltage to a
suitable level. Theoretically,
a variable resistor
of the proper value
could be used as an output
control since voltage is inversely
proportional to resistance
as we saw when studying Ohm's Law. Ohm's Law also stated that the
amperage is directly proportional to
the voltage. This being so, you can see that adjusting
the output control will also adjust
the amperage or welding current. 1.8.5.8
After the arc is initiated and current
begins to flow through the secondary or welding
circuit, the voltage in that circuit will be 32 volts because it is then being
controlled by
the output control. 1.8.6
Power
Requirements - We can make another calculation
by looking back at Figure
15, and that is power consumption. Earlier, we explained that the watt was
the unit of electrical
power and can be calculated by the formula: Watts
= Volts × Amperes 1.8.6.1
From Figure 15, we can see that the
instantaneous power in the secondary circuit
is: Watts = 32
× 300 Watts
= 9600 Watts 1.8.6.2
The primary side of our transformer
must be capable of supplying 9600 watts also
(disregarding losses due to heating, power factor, etc.), so by rearranging the
formula, we can
calculate the required supply line current or amperage: Amperage
= Watts ÷ Volts A
= 9600 ÷ 230 = 41.74 Amps 1.8.6.3
This information establishes the approximate
power requirements for the welder, and
helps to determine the input cable and fuse size necessary.
FIGURE 15 9600
WATTS 9600 WATTS
230 TURNS 80
TURNS 80
OCV OUTPUT
CONTROL 230
VOLTS PRIMARY
SECONDARY 41.74
AMPS SIMPLIFIED
WELDING TRANSFORMER 32
VOLTS 300 AMPS
