Lincoln Electric SVM151-A service manual OVER-VOLTAGE Protection

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THEORY OF OPERATION

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PROTECTION FEATURES

The Multi-Weld 350 design features electronic protec- tion systems to help assure reliable operation even under adverse conditions. These systems include:

FAN AS NEEDED (F.A.N.)

The cooling fan will turn on when the arc starts and remain on for about a minute after the arc is out to cool down the power components.

This feature electronically controls the fan so it does not run continuously when the power switch is turned on. This will minimize the amount of contaminate and clogging debris that may be drawn into the converter.

The “Central-Air” system design intakes lower velocity air through the higher side louvers and blows it out through the lower back louvers with higher velocity.

OVER-CURRENT PROTECTION

The maximum output current of the Multi-Weld 350 is electronically limited so as not to exceed 375 amps average and 500 amps peak to protect internal power components. When the current load starts to exceed these limits, the output is reduced (lower voltage) to sustain maximum levels until the current is reduced, even to a shorted output.

Prolonged output at this maximum current limit level may eventually over heat the converter’s internal power components, causing over-temperature shut- down.

Short circuit protection is also provided to reduce max- imum output current to about 200 amps if the output voltage is reduced, by loading or current limiting, to below 14 volts for over 7 seconds (indicating a shorted output). The output current must be interrupted to reset this reduced protective level.

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OVER-TEMPERATURE SHUTDOWN

The Multi-Weld 350 has a temperature sensing ther- mostat on the input diode heat sink to protect the power components within the converter from overheat- ing. If this thermostat temperature exceeds about 95 degrees C (203 degrees F), the converter will electron- ically shut off the output and turn on the Thermal Shutdown (yellow) Light until the thermostat is cooled enough to reset.

This maximum 200 amp short circuit level will allow using the Multi-Weld 350 for “pipe-thawing” applica- tions without causing over-temperature shutdown.

CAUTION

When the contactor recloses, the converter output will reactivate. Switching OFF input power prevents unex- pected reactivation.

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CAUTION

When the thermostat resets, the converter output will reactivate. Switching OFF input power prevents reac- tivation but also shuts off the cooling fan, which pro- longs the reset time.

During over-temperature shutdown the panel displays will be appropriate for the non-welding mode. However, the fan will remain running and the Thermal Shutdown Light will be lit until reset.

This feature protects internal components of the con- verter from excessive voltage levels.

OVER-VOLTAGE PROTECTION

The Multi-Weld 350 input contactor will open if the input supply voltage is above 113 VDC, and it will automati- cally reclose if the voltage drops back to 113 VDC. During over-voltage shutdown the panel displays will be as appropriate for the non-welding mode.

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MULTI-WELD 350