CHOPPER TECHNOLOGYFUNDAMENTALS
The new era of welding machines such as the Ranger
305D 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
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 90 VDC. Thecurrent 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
theinductor 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 offtime 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
RANGER 305D
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3 PHASE
ALTERNATOR DCRECTIFIER
AND FILTER INDUCTOR
AND DIODE ARC
ARC
CONTROL
SOLID STATE
SWITCH
INDUCTOR
SWITCH
DIODE ARC
CURRENTWITH SWITCH OPEN
CURRENTWITH SWITCH CLOSED
90 VDC