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CHOPPER TECHNOLOGY
FUNDAMENTALS
The new era of welding machines such as the
Commander 300, employ a technology whereby a DC
source is turned on and off (chopped up) at high speed,
then smoothed through an inductor to control an arc.
Hence the name “Chopper.” The biggest advantage of
the chopper technology is the high-speed control of the
arc, similar to the inverter machines. A block diagram
for this is as follows:
In this system, the engine drives a three-phase alter-
nator, which generates power that is rectified and fil-
tered to produce about 85VDC. The current is
applied through a solid state switch to an inductor. By
turning
the switch on and off, current in the inductor and the
arc can be controlled. The following diagram depicts
the current flow in the system when the switch is open
and closed:
When the switch is closed, current is applied through
the inductor to the arc. When the switch opens, current
stored in the inductor sustains flow in the arc and
through the diode. The repetition rate of switch closure
is 20Khz, which allows ultra-fast control of the arc. By
varying the ratio of on time versus off time of the switch
(Duty Cycle), the current applied to the arc is con-
trolled. This is the basis for Chopper Technology:
Controlling the switch in such a way as to produce
superior welding.
THEORY OF OPERATION
E-7 E-7
COMMANDER 300
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3 PHASE
ALTERNATOR
DC RECTIFIER
AND FILTER
INDUCTOR
AND DIODE
ARC
ARC
CONTROL
SOLID STATE
SWITCH
INDUCTOR
SWITCH
DIODE
ARC
CURRENT WITH SWITCH OPEN
CURRENT WITH SWITCH CLOSED
85VDC