Lincoln Electric DC-655 service manual Theory of Operation, General Description

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E-2 E-2

THEORY OF OPERATION

FIGURE E.2 – INPUT LINE VOLTAGE, CONTACTOR, RECONNECT,

FAULT PROTECTION, MAIN AND CONTROL TRANSFORMERS

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CONTROL

TRANSFORMER

115VAC

CR2

R

E

C

O

N

N

E

C

T

CONTACTOR

CR1

42VAC

CONTROL

BOARD

TRANSFORMER

FAULT PROTECTION

							OUTPUT		ARC FORCE
							CONTROL
32VAC						OUTPUT			CONTROL
				FIRING		CONTROL SIGNAL
32VAC
32VAC				BOARD
				G	S
14-pin		115VAC	Fan	A	I
				T	G
Amphenol		Receptacle	Motor		N	Fan
				E
					A	Thermal
					L	Sensor
T				SNUBBER			CONTROL
	S						BOARD		MODE
R				FAN
	T
E
M	R	115VAC		BOARD					SWITCH
I	I
N	P
A
L				GATE SIGNAL
							F
42VAC
							E
							E
MAIN							D
							B
TRANSFORMER							A
							C		POSITIVE
							K
									TERMINAL
							SHUNT	F
								E
								E
42VAC 10VAC10VAC							LATCHING	D
							RESISTOR	B
				SCR BRIDGE				A	HIGH
								C	NEGATIVE
						CHOKE		K	TERMINAL
TO OPTIONAL
METER BOARD

LOW

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GENERAL DESCRIPTION

The DC-655 is a three-phase, SCR controlled DC power source. It is capable of either constant current or constant voltage output. It is rated at 650 amps, 100% duty cycle with outstanding arc characteristics for multiple welding processes.

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 volt- age, low current input power to a lower voltage, high- er current output. The finishes or “neutrals” of the main secondary coils are connected together, and the six starts of the secondary windings are connected to the rectifier assembly.

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INPUT LINE, CONTACTOR, RECONNECT, FAULT PROTECTION AND TRANSFORMERS

The desired three-phase input power is connected to the DC-655 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 trans- former. The secondary of the control transformer sup- plies 115 VAC power to the control board transformer and to the input contactor through the fault protection relay. The control board transformer supplies 42 VAC to the control board.

In addition, the main transformer also has eight isolat- ed secondary windings. There are three 32 VAC wind- ings, which provide power and “timing” to the firing board. The 115 VAC winding powers the fan motor and provides 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 up to 10 amps at the 14-pin MS type connector. Three other isolated coils are used to power the optional digital meter PC board. One winding is rated at 42 VAC, and the other two are each rated at 10 VAC.

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

IDEALARC DC-655