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Curtis PMC 1204X/1205X/1209/1221 Manual
mance variations resulting from variations in controller operating environment
temperatures.
Thermal protection
Because of their efficiency and thermal design, Curtis PMC controllers should
barely get warm in normal operation. Overheating can occur, however, if the
controller is undersized for its application or otherwise overloaded. If the internal
temperature of the controller exceeds 75°C (167°F), the main and plug current
limits decrease steadily until they are reduced to zero at 95°C (200°F). At the
reduced performance level, the vehicle can be maneuvered out of the way and
parked. The controller shifts frequency during overtemperature from its normal
15 kHz to 1 kHz, providing an audible tone alerting the operator to the
overtemperature. (
NOTE
temperature. This ensures full braking capability even in overtemperature condi-
tions. However, it may result in premature plug diode failure due to excessive
thermal stresses.)
Full current limit and performance return automatically after the controller
cools down. Although this action is not damaging to the controller, it does
suggest a mismatch. If thermal cutback occurs often in normal vehicle operation,
the controller is probably undersized for the application and a higher current
model should be used.
The controller is similarly protected from undertemperature. Should its
internal temperature fall below -25°C (-13°F), the current limit decreases to
approximately one-half of the set current. When the controller warms up, full
current limit and performance return automatically.
Throttle pot fault protection
To prevent uncontrolled operation, these controllers shut off the motor in the
event of an open circuit fault in the throttle or its wiring. The standard
configuration is a two-wire pot ranging from 0 ohms for full off to 5000 ohms for
full on; if the controller detects an abnormally high throttle input (more than
about 1.5 times the normal input resistance), it shuts off its output to the motor,
thus preventing a runaway. The controller returns to normal operation when the
fault (e.g., broken potbox wiring, broken connectors) has been repaired.
Undertemperature
See Thermal protection.
Undervoltage protection
The control circuitry requires a minimum battery voltage to function properly.
The controller is therefore designed so its output is gradually reduced if the
: The plug current limit can be made independent of
(runaway protection)
GLOSSARY
41
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