Two thermostats protect the CV-400 from excessive
operating temperatures and overload conditions.
Excess operating temperatures may be caused by
insufficient cooling air or by operating the machine
beyond the duty cycle and output rating. The primary
thermostat is located on the nose of the center bottom
primary coil. The secondary thermostat is attached to
the lead connecting the secondaries. Both thermostats
are connected in series with the trigger circuits. If the
machine is over-heated, the thermostats will open and
output will be zero. The thermal protection light will
glow and the fan will continue to run. See Figure E.4,
CV-400 Trigger And Thermal Light Circuit. Under nor-
mal conditions the Thermal Light is "shorted out" by
the circuit breaker and thermostat circuit. If the ther-
mostats or the circuit breaker opens, more current will
flow through the Thermal Light circuit, and the light will
glow.

The power source is also protected against overloads
on the SCR bridge assembly through the solid state
fault protection circuit. This circuit senses an overload
on the power source and limits the output to approxi-
mately 550 amps by phasing back the SCRs.

Protection is also provided to protect the circuitry from
accidental grounds.

If the customer accidentally

"grounds" 75, 76, or 77 to the positive output lead, the
CV-400 output will be reduced to a very low value, thus
preventing any damage to the machine. If the ground
occurs between 75, 76, and 77 and the negative output
lead, one of the PC board electronic "self-restoring"
fuses will blow, preventing any machine damage. After
the ground is cleared, the fuses automatically reset
within a few seconds.

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