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section 6
6.11 low current range
The EPP-450 operates in either LOW or HIGH current output ranges. The LOW range is used for marking from 10 to 100
amperes and cutting from 35 to 100 amperes. The HIGH range is used for cutting from 50 to 450 amperes.
In the HIGH range, both the left and right power sources are used. Each side contributes 50% of the total output current.
The left side acts as a master power source by synchronizing the switching of the right side to its own switching frequency
of 10 KHz.
In the LOW range, only the left power source is used. The normally open contact, K13(6, 9) prevents T7 from supplying bias
supply power to PCB-3, the right PWM / IGBT Gate Drive PC Board. This disables the right side.
The same K13 contact (square labeled "D" on the schematic diagrams) places the EPP-450 in the HIGH current mode. In
addition to providing bias power to PCB-3 in the HIGH current mode, this 115 VAC is fed into PCB-10 P1-2.
PCB-10 performs two functions. With no input on PCB-10 P1-2, PCB-10 scales the 0 to 10 VDC current reference signal for 0
to 100 amperes (LOW range). In the LOW range, PCB-10 P4-11 / P4-12 provides a signal to PCB-2 P4-1 / P4-2. This signal com-
mands PCB-2, the left (master) PWM / IGBT Gate Drive PC Board to change the switching frequency from 10 KHz to 25 KHz.
The higher switching frequency results in the more power dissipation by the heat sinks on PCB-3. Therefore, in the LOW
current mode, a small fan, M5, turns on to provide additional cooling. M5 does not operate in the HIGH current mode.
6.12 electrode current transducer circuit
The Electrode Current Transducer Circuit provides a galvanically isolated signal to the plasma control indicating the power
source output current. The scaling of the signal is: VOUT = IELECTRODE/100. For example, 200A results in 2.0V output. The
scaling is the same for both high and low current ranges. The output signal resistance is 100 Ohms.
PCB11 receives the signal from the Hall Effect Transducer and sends the signal through FN5 to J1-Y (+) and J1-J (-). PCB11 sup-
plies +15V and -15V to operate the transducer. It also buffers the signal to prevent damage to the transducer from voltage
transients generated outside the power source.
TO SHUNT NEG.
TO PILOT ARC CONTACTOR, K4-T1
ELECTRODE
CURRENT
TRANSDUCER
NOZZLE
(TB10)
ELECTRODE
1
FN1
3
ELECTRODE CURRENT TRANSDUCER CIRCUIT
J1-J & TB1-5, DC
SIGNAL COMMON
(NEG), ALSO
SHOWN ON PAGE 2
P1-4
P1-3
TD3
WORK
+
2
1
2
FN2
3
2
4
+
J1-Y
FN5
1V=100A
-
J1-J
1
3
TB1-5
P4-8
P4-6
-15S
P4-5
S COM
PCB11
P4-1
SIGNAL -
P4-2
SIGNAL +
P4-4
+15S
P1-2
P1-1
P3-1
62
troubleshootinG
-
+
P4-7
50
50
S
ANALOG
SCALING
BOARD
S BIAS
P3-2
20V 20V
H2
T11
PRI: 120V
120V
SEC: 40VCT
H1
N
H
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