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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-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.
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.
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.
This maximum 200 amp short circuit level will allow
using the Multi-Weld 350 for “pipe-thawing” applica-
tions without causing over-temperature shutdown.
When the contactor recloses, the converter output will
reactivate. Switching OFF input power prevents unex-
pected reactivation.
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.
E-6 E-6
THEORY OF OPERATION
MULTI-WELD 350
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CAUTION