Hypertherm MAX200 Plasma Electrode 220021 Nozzle 020608 Shield 020424 Swirl Ring 020607 For Plasma Torch

The MAX200 plasma unit: uses a “chopper” control circuit to stabilize the DC output current of the system. The chopper is a switching circuit that is AC activated and outputs a square wave with the peak value being equal to its DC input (283 VDC in the case of the MAX200).

Circuit Description:

The following is a description of the operation of the chopper section of the MAX200 power supply. See wiring diagram 013-4-179 as well as component figures in the Parts List section for reference.

"Snubber" Section:

The “snubber” section supplies 283VDC to the chopper PCBs.

Incoming AC voltage enters dual snubber PCBs (PCB1, PCB3) and becomes rectified to DC through diodes D1- D6. Varistors MOV1, MOV2, and MOV3 limit transient voltage spikes. Capacitors C1-C6 are charged to 283VDC. Bleeder resistors R7 and R8 allow capacitors C1-C6 to discharge when the unit is not in use.

Chopper Section:

Chopper modules PCB2 and PCB4 are powered by 14VAC from T3 and T4. Current control, which controls pulse duration (duty cycle) of the choppers is selected from Voltage/Current (V/C) Remote or thumbwheel switch. This information is on pins 5 and 6 of REC1 on the chopper PCBs. A longer pulse duration yields a higher output current, and a shorter pulse duration yields a lower output current. The chopper module generates a square wave of output current at the input DC voltage (283V) at an operating frequency of16KHZ.

The output of the chopper goes to the surge injection circuit (R4, C7), filter inductors (L1, L2), chopper module diode, torch electrode, transferred arc sensor (CS1), and shunt resistors (R1, R2, R3). Fuses F3 and F4 protect each chopper from exceeding 125 amps of output.

Surge Injection:

Circuit Surge injection circuit capacitor C7 charges to the open circuit voltage of the chopper module (283VDC). When the arc is transferred from the electrode to the workpiece (see THEORY OF OPERATION: HIGH FREQUENCY later in this section for more information on arc transfer), C7 discharges through the 5Ω R4 and on to the torch electrode. Current provided by C7 maintains the cutting arc, while the chopper module and rectifier circuit responds to the current load of the cutting arc. Filter inductors (L1 and L2) and the chopper module diode begin to function once the arc is established.

Filter Inductor and Chopper Module Diode Circuit:

During the off interval of the chopper module output cycle, the magnetic fields of L1 and L2 will collapse, and their polarity will reverse (looking at page 1 of wiring schematic inductors L1 and L2 will now be negative on their left side). This action of the inductor will forward bias the chopper output diode causing current flow to pass through it from bottom to top. L1 and L2 then maintain the cutting arc current flow during the “off” chopper cycle.

Current Sensor:

Circuit The current sensor coil CS1 is a magnetic device that produces a voltage when current is sensed from the cable passing through it. The cable is directly attached to the workpiece, and the sensing of current will occur when the arc is transferred. This type of sensing phenomena is known as the Hall effect. This voltage is transmitted from pin 3 on PL12, to pin 14 of REC2 on the Control PCB (PCB7).

Shunt Circuit:

R1 and R2 are shunt resistors for choppers CH1 and CH2, respectively. R3 carries the sum of the currents flowing to R1 and R2. The voltage taken across R1 and R2 is sent to Control PCB7. This shunt voltage will be compared with the current control voltage. Any difference between the two voltages is sensed, and the output control signal to the chopper module is adjusted to correct any error.

Tube 020963

Electrode 120547

Electrode 220021

Swirl Ring 020617

Swirl Ring 020604

Swirl Ring 020607

Nozzle 020616

Nozzle 020605

Nozzle 020689

Nozzle 020611

Nozzle 020608

Retaining Cap 120837

Retaining Cap 020423

Shield 020448

Shield 020424

Shield 020688

Hypertherm MAX200 Plasma Electrode 220021 Nozzle 020608  Shield  020424 Swirl Ring 020607