Lincoln Electric PRO-CUT 25 Service Manual page 29

E-5
SW1
L1 RL3
A
300uH R1
10/10W
B
V1
L1
V2
230V
RL1
115V
L1
Voltage Board
12VDC
Air
Purge
Solenoid
Switch
1
OUTPUT SECTION AND TORCH
The output section contains a relay which, upon
receiving a pilot signal from the control board will
enable the operation of a pilot arc or a cutting arc. The
printed circuit board mounted current sensor regulates
the pilot and cutting current. The output choke, which
is in series with both the pilot circuit and the cutting
circuit, provides current filtering to enhance arc stabil-
ity.
The PCT 20 torch uses a patented touch start mecha-
nism that provides superior starting performance over
other touch start systems. The torch head consists of
3 major parts: torch body, insulator and piston. The
insulator provides an electrical barrier between the
piston and torch body. The piston provides a path for
electrical current to the electrode. The piston also dri-
ves the electrode to the nozzle for arc initiation. The
torch body contains the main torch components: the
trigger, pilot arc, cutting arc, and air flow systems are
included.
A copper nozzle with a patented internal swirl is used
to focus the arc. A small, precise hole in the end of the
nozzle constricts the arc and increases the current
density. As the air enters the torch head, it is directed
THEORY OF OPERATION
FIGURE E.5 – PLASMA OUTPUT SECTION AND TORCH
AC AC
RL2
CP CP
RL2
CP CP
RL2
AC
AC
RL1
RL2
115VAC
T1
CN1 CN2
15VAC
1 9
15VAC
2 10
SAFETY
3 5
+28VDC
4 6
SEC GND
5 3
OVLOAD
6 22
115/230
Input
7 2
+12VDC
8 20
8 6 17 9 3
CN1
Display LED's
Q1a,b,c
IRG4BC30W
C26
PRI
+
R1
CP
C1a,b
C12
CP
+
R2
C2a,b
Q2a,b,c
IRG4BC30W
CN1
15 16 12 18 14 1 11 4 13 7 19 24 21 23 8 17 1 2 3
1 2 18 14 7 15 4 11 5 16 10 12 13 23 22 24
Output Control
Control Board
between the electrode and nozzle for maximum elec-
trode cooling. A portion of the cooling air exits in the
chamber through vents in the side of the nozzle. A
swirl texture located inside the bottom of the nozzle
increases the plenum air swirl strength, and improves
arc start reliability and parts-in-place verification.
Plasma arc initiation occurs as follows: First, in the idle
state, a spring inside the torch head pushes the piston
and electrode forward to make continuity with the noz-
zle. When the trigger is pulled, air flow begins and cre-
ates enough back force on the electrode to overcome
the force of the spring. However, the solenoid valve
allows enough forward force on the piston to maintain
continuity between the consumables.
continuity has been verified, output current is estab-
lished and regulated. Once the current stabilizes, the
solenoid valve turns off, removing the forward force on
the piston. The back pressure drives the piston and
electrode away from the nozzle, creating the plasma
arc. The air stream forces the arc out the orifice of the
nozzle. This appears as a pilot arc, which can then be
transferred for cutting.
PRO-CUT 25
Lout
D10
BS1
WRK
240uH
8A
T2
+12VDC TRANSFER
SEC
D11
RL1 NZL (2)
C14
R24
6.8k/5W
SHUNT
EL (3)
C13
SH- SH+
CN3
1
2
3
4
Main Inverter Board
4
E-5
WORK CLAMP
PT
12VDC
After this