THEORY OF OPERATION
MOTOMAN 3-3 Spot Welding Manual for Medar
and voltage is stepped up or down is equal to the ratio between the number of turns
of wire in the coils forming the primary and secondary windings of the
transformer. Consider the steel that needs 10,000 Amps (10 KA) of current to be
welded in a factory that can only provide 200 Amps (0.200 KA). If the welding
transformer had 100 turns on the primary and 2 turns on the secondary, the ‘turns
ratio' would be 100 to 2, or more simply, 50 to 1. The 200 Amp current in the
primary would then be converted (stepped up) to 10,000 Amps (200 Amps x 50
turns = 10,000 Amps) in the secondary, which would yield enough amperage to
make a weld.
Figure 3-2 Primary vs. Secondary Voltage
3.3.2 Voltage
If current is the amount of electricity flowing, then Voltage (measured in Volts) is
the pressure or force that's causing the flow. A good analogy is water flowing
through a pipe. A larger voltage will result in greater water pressure, which will
cause more water (current) to flow through the pipe. Using the transformer
example above, after the 200 Amps at 500 Volts on the primary passes through the
transformer coils, the secondary amperage increases to 10,000 Amps, but the
voltage actually drops to 10 Volts. This decrease in voltage occurs because the
amount of power coming out of a transformer isn't actually increased, but
exchanged.
3.3.3 Ohm’s Law
Ohm’s Law expresses the relationship between voltage, current, and resistance.
The relationship is expressed as voltage equals current times resistance (E = I x R).
• E – Electromagnetic Force (voltage)
• I – Current (pure current)
• R – Resistance (pure resistance)
Secondary
Windings
(2 turns)
Primary
Windings
(100 turns)
Magnetic
Core
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