Lincoln Electric SVM188-A service manual Theory of Operation, Input Circuit and Main TRANS- Former

E-2	THEORY OF OPERATION	E-2
	FIGURE E.2 - INPUT AND TRANSFORMER

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CONTROL	POWER
TRANSFORMER	SWITCH
115VAC
	•
Pilot
Light
w
•	CR2
Secondary
Thermostat
Primary
Theromstat
1CR Coil
	R
	E
	C
	O
	N
	N
	E
	C
	T

CONTACTOR

CR1

							TERMINAL
							STRIP 1
								OUTPUT
FAULT PROTECTION								CONTROL
								SWITCH
							OUTPUT
32VAC						OUTPUT	CONTROL
32VAC				FIRING		CONTROL SIGNAL
32VAC				BOARD
				G	S
14-pin		115VAC	Fan	A	I
				T	G
Amphenol		Receptacle	Motor	E	N
					A
					L
T		115VAC					CONTROL
	S
R		•					BOARD		MODE
	T
E			OUTPUT						SWITCH
I	I
M	R
N	P	TERMINAL
AL	2
			SWITCH				F
42VAC		115VAC					E
							E
MAIN							D
							B
TRANSFORMER							A
							C		POSITIVE
							K
									TERMINAL
							SHUNT	F
								E
								E
							LATCHING	D
							RESISTOR	B
				SCR BRIDGE				A
								C	NEGATIVE
						CHOKE		K	TERMINAL

GENERAL DESCRIPTION

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The DC-600 is a three-phase, SCR controlled DC power source. It is capable of either constant current or constant voltage output. It is rated at 600 amps, 100% duty cycle with outstanding arc characteristics for multiple welding processes.

INPUT CIRCUIT AND MAIN TRANS- FORMER

The desired three-phase input power is connected to the DC-600 through an input contactor located in the input box at the rear of the machine. Two phases of the input line are also connected to the control transformer. The secondary of the control transformer supplies 115 VAC power to the control board and to the input con- tactor through the fault protection relay.

A reconnect panel allows the user to configure the machine for the desired input voltage. This three- phase AC input is applied to the primary of the main transformer. The transformer changes the high voltage, low current input power to a lower voltage, higher cur- rent output. The finishes or “neutrals” of the main sec- ondary coils are connected together, and the six starts of the secondary windings are connected to the SCR rectifier assembly.

In addition, the main transformer also has five isolated secondary windings. There are three 32 VAC windings, which provide power and “timing” to the firing board. The 115 VAC winding powers the fan motor and pro- vides the user with up to 20 amps of 115 VAC auxiliary power at the receptacle or 14-pin MS type connector. The 42 VAC winding provides 10 amps of power to the 14 pin MS type connector to power a wire feeder.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion

DC-600