Lincoln Electric SVM188-A service manual Thermal Protection

E-4	THEORY OF OPERATION	E-4
	FIGURE E.2 - GENERAL DISCRIPTION

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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

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PROTECTIVE DEVICES AND

SHUTDOWN CIRCUITS

THERMAL PROTECTION REMOTE CONTROL FAULT PROTECTION

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This welder has thermostatic protection from excessive duty cycles, overloads, loss of cooling, and high ambi- ent temperatures. When the welder is subjected to an overload or loss of cooling, a thermostat will open. The input contactor will open and remain open until the machine cools; the white POWER light stays illuminat- ed. No welding is possible during this cool down peri- od. The machine will reset automatically when the ther- mostat cools.

OVER CURRENT PROTECTION

The power source is also protected against overcur- rents in the SCR bridge assembly through an electron- ic protection circuit. This circuit senses currents over 780 amps on the power source and opens the input contactor should the overcurrent remain for a predeter- mined time (the white POWER light stays illuminated). The predetermined time varies with the amount of overcurrent; the greater the overcurrent, the shorter the time. The input contactor will remain open until the power source is manually started by resetting the POWER ON/OFF toggle switch.

The power source circuitry is protected from faults on the control circuit leads (#75, 76, or 77). If any of these leads become common with either of the output leads, the DC-600 will either shut down completely (control lead fault to Negative Output), or will remain at mini- mum output (control lead fault to Positive Output) thus preventing any damage to the DC-600. If DC-600 shuts down, (input contactor opens and white POWER light stays illuminated) it must be manually started by reset- ting the POWER ON/OFF toggle switch.

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

DC-600