A-12
Curtis 1244 Manual, Rev. E
APPENDIX A: GLOSSARY
Undervoltage protection
Undervoltage protection automatically cuts back the controller output if bat-
tery voltage is detected below the undervoltage point at startup, or when the
battery voltage is pulled below the undervoltage point by an external load. e
under voltage cutback point is determined by the battery voltage parameter,
which should be identical to the system’s nominal battery pack voltage—see
Section 3, page 46.
During normal operation, the controller duty cycle will be reduced when
the batteries discharge down to less than the undervoltage level. If the motor
current is such that the batteries are being pulled below the minimum point,
the duty cycle will be reduced until the battery voltage recovers to the minimum
level. In this way the controller “servos” the duty cycle around the point which
maintains the minimum allowed battery voltage.
If the voltage continues to drop below the undervoltage level to a severe
undervoltage condition (due to battery drain or external load), the controller
continues to behave in a predictable fashion, with its output disabled.
Watchdog (external, internal)
e external watchdog timer guards against a complete failure of the micropro-
cessor, which would incapacitate the internal watchdog timer. is independent
system check on the microprocessor meets the EEC’s requirement for backup
fault detection.
e external watchdog timer safety circuit shuts down the controller (and
the microprocessor) if the software fails to generate a periodic external pulse
train. is pulse train can only be created if the microprocessor is operating.
If not periodically reset, the watchdog timer times out after 15–20 msec and
turns o the controller. e external watchdog also directly shuts down the
PWM drive to the MOSFETs. It can only be reset by cycling KSI.
e internal watchdog timer must be reset periodically by correct sequen-
tial execution of the software. If not reset, the internal timer times out and
the microprocessor is “warm booted.” is causes the microprocessor to shut
down its outputs—thus shutting down the controller—and attempt to restart.
Welded contactor checks
e 1244 controller checks for a welded main contactor at startup. If a welded
contactor is detected, the controller inhibits its output until the fault is removed
and the keyswitch power is cycled. A welded main contactor fault is indicated in
the programmer’s Diagnostics Menu as well as by the controller’s Status LED.
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