Lincoln Electric V250-S service manual Protection Circuits, Overload Protection

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E-6 THEORY OF OPERATION E-6

PROTECTION CIRCUITS

Protective circuits are designed into the V250-S machine to sense trouble and shut down the machine before the trouble damages the internal machine com- ponents. Both overload and thermal protection cir- cuits are included.

OVERLOAD PROTECTION THERMAL PROTECTION

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The V250-S is electrically protected from producing high output currents. Should the output current exceed 290 amps, an electronic protection circuit will reduce the current to less than 200 amps. Lincoln Electric refers to this current reduction as “Fold Back”. The machine will continue to produce this low current until the protection circuit is reset. Reset occurs when the output load is removed.

A protection circuit is included to monitor the voltage across the input filter capacitors. In the event that the capacitor voltage is too high, the protection circuit will prevent output.

On new installations, the protection circuit may pre- vent output, due to unbalanced capacitor leakages, providing the following circumstances are met:

1.Machine is connected for 380 - 460VAC input.

2.Machine did not have power applied for many months.

3.Improper connections.

4.Internal component damage.

Thermostats protect the machine from excessive operating temperatures. Excessive temperatures may be caused by a lack of cooling air or operating the machine beyond the duty cycle and output rating. If excessive operating temperature should occur, the thermostat will prevent output voltage or current and the thermal indicator light will glow.

Thermostats are self-resetting once the machine cools sufficiently. If the thermostat shutdown was caused be excessive output or duty cycle and the fan is oper- ating normally, the power switch may be left on and the reset should occur within 15 minute period. If the fan is not turning or the air intake louvers were obstructed, then the power must be switched off for 15 minutes in order to reset. The fan problem or air obstruction must be corrected.

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NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

INVERTEC V250-S