Protective Circuits - Lincoln Electric INVERTEC V300-I Service Manual

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PROTECTIVE CIRCUITS

Protective circuits are designed into the
Invertec machine to sense trouble and shut
down the machine before the trouble dam-
ages the internal machine components.
Both overload and thermal protection cir-
cuits are included.
OVERLOAD PROTECTION
The machine is electrically protected from
producing high output currents. Should the
output current exceed 340 to 360 amps, an
electronic protection circuit will reduce the
current to approximately 150 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 out-
put load is removed.
A protection circuit is included to monitor
the voltage across input filter capacitors. In
the event that the capacitor voltage is too
high, the protection circuit will prevent out-
put. The protection circuit may prevent out-
put, if any of these circumstances occur:
1. Capacitor conditioning is required
(Required if machine has been off for
prolonged periods of time.)
2. Line surges over 500 VAC
3. Internal Component damage
4. Improper connections
INVERTEC V300-I
THEORY OF OPERATION
THERMAL PROTECTION
Thermostats protect the machine from
excessive operating
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. The meter will
remain on during this time.
Thermostats are self-resetting once the
machine cools sufficiently. If the thermostat
shutdown was caused by excessive output
or duty cycle and the fan is operating nor-
mally, the Power Switch may be left on and
the reset should occur within a 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 also be corrected.
temperatures.