Curtis PMC 1209B/1221B/1221C/1231C Manual
41
GLOSSARY
approximately one-half of the set current. When the controller warms up, full
current limit and performance return automatically.
Throttle microswitch
Curtis PMC potboxes and footpedals are typically equipped with microswitches.
It is recommended that these switches be used to open the main contactor and the
controller’s KSI input when the throttle is fully released. This adds a level of safety
protection by disconnecting battery power from the motor and controller when-
ever the operator releases the throttle. If you are not using a throttle with a built-
in microswitch, it is recommended that you add one to your system.
Throttle pot fault protection (runaway 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
battery voltage falls below a certain level. Cutback voltages for the various models
are listed in the specifications (Appendix C). Reducing the output to the motor
allows the battery voltage to recover, and an equilibrium is established in which
the battery supplies as much current as it can without falling below the cutback
voltage.
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