Theory of operation, Protection circuits – Lincoln Electric INVERTEC V250-S User Manual
Page 30
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
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.
THERMAL PROTECTION
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.
INVERTEC V250-S
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.