Hypertherm MAX42, Service Manual

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THEORY OF OPERATION
MAX42 Service Manual Page 2-3
CIRCUIT DESCRIPTIONS
The MAX42 Power Unit is functionally divided into control circuits and inverter
circuits. Note that some of the printed circuit boards and components serve in both
functional areas. Refer to Section 5,
Wiring Diagrams & Schematics
, for all
associated wiring diagrams, circuit board schematics, and the pneumatic system flow
diagram.
Control Circuits
• Power Supplies
In addition to the main power inverter, there are two control power supplies in the
MAX42 power unit. One of the power supplies, on PCB2, has two functions: (1)
It supplies power to relays K1 and K2 to bypass the two 5-ohm surge resistors
R1 and R2. (2) It supplies power to the inverter control circuitry located on the
modulator board PCB12. The other control power supply, comprised of control
power supply board PCB13 and T5, su15 VDC power to operate fan M1
and to power the control circuits on control board PCB14.
• Control Board PCB14
This circuit board performs the following functions: (1) It monitors the pressure
switch PS1 and the thermostat TS1. Indicator LT1 lights when the operating
temperature and the incoming gas pressure are within operating limits. It goes
out when either pressure switch PS1 opens because the incoming gas pressure
is too low or when thermostat TS1 opens because the duty cycle rating was
exceeded causing the power unit to overheat. (2) It controls the sequence of
function required to generate plasma as follows:
- Turns on the inverter when the torch switch button is pressed.
- After a short delay, turns on the air solenoid valve V1 to blow back the
electrode.
- Monitors the pilot arc controller board PCB15 for arc transfer.
- Ramps the current control command from the pilot arc level (18-20 amps) to
the cut current selected by the operator.
- Turns the inverter off if the arc transfer does not occur within three seconds.
- Provides indication to the operator that the power is on (LT2 lit) and the
pressure and temperature interlocks are okay (LT1 is lit).
• Feedback
The output current from the inverter flows through the shunt (R1, R2, and R3)
located on I/O board PCB1. The signal from the shunt is sent to the modulator
board PCB12.