Chopper Technology Fundamentals - Lincoln Electric COMMANDER SVM145-B Service Manual

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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.
3 PHASE DC RECTIFIER
ALTERNATOR
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
85VDC
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
THEORY OF OPERATION
SOLID STATE
AND FILTER
CONTROL
SWITCH
DIODE
CURRENT WITH SWITCH CLOSED
COMMANDER 300
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:
INDUCTOR
SWITCH AND DIODE
ARC
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:
INDUCTOR
CURRENT WITH SWITCH OPEN
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.
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ARC
ARC