BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
Page
7
October 2002
is enabled when the armature current is less than the value
set by Function 24 and the accelerator input voltage is less
than 1 volt. It is important to note that this function is used
to optimize motor and control performance, and this setting
will be determined by GE and OEM engineers at the time of
vehicle development. This setting must not be changed by
field personnel, without the permission of the OEM.
Section 2.1.4.b Speed Limits
This feature provides a means to control speed by limiting
motor volts utilizing three "adjustable speed limits. This
motor volt limit regulates top speed of the transistor
controller, but actual truck speed will vary at any set point
depending on the loading of the vehicle. Each speed limit
can be adjustable with the Handset using Functions 12 and
13.
Section 2.1.5 Ramp Operation
Section 2.1.5a Ramp Start
This feature provides maximum control torque to restart a
vehicle on an incline. The memory for this function is the
directional switch. When stopping on an incline, the
directional switch must be left in its original or neutral
position to allow the control to initiate full power when
restarted. The accelerator potentiometer input will
modulate ramp start current.
Section 2.1.5b Anti-Rollback
This feature provides retarding torque to limit rollback
speed in the non-travel direction when the ACC pedal is
released when stopping on a grade, or when the brake
pedal is released when starting on a grade. This feature
forces the vehicle to roll very slowly down the grade when
accelerator or brake is released. Because the vehicle can
gain significant speed during roll-back, the torque needed
to re-start on the ramp is lower than an unrestricted roll-
back speed.
Section 2.1.6 On-Board Coil Drivers & Internal Coil
Suppression
Coil drivers for the LINE and 1A, or bypass, contactors are
on-board the control card. These contactors must have
coils rated for the vehicle battery volts.
Section 2.2 System Protective Override
Section 2.2.1 Static Return to Off (SRO)
This inherent feature of the control is designed to require
the driver to return the directional lever to the neutral
position anytime he leaves the vehicle and returns.
Additionally, if the seat switch or key switch is opened, the
control shuts off and cannot be restarted until the
directional lever is returned to neutral. A time delay of
approximately 2 seconds is built into the seat switch input
to allow momentary opening of the seat switch, if a bump is
encountered.
Section 2.2.2 Accelerator Volts Hold Off
This feature checks the voltage level at the accelerator
input whenever the key switch or seat switch is activated.
If, at start up, the voltage is less than 3.0 volts, the control
will not operate. This feature assures that the control is
calling for low speed operation at start up.
Section 2.2.3 Pulse Monitor Trip (PMT)
The PMT design contains three features which shut down,
or lock out, control operation if a fault conditions occurs
that would cause a disruption of normal vehicle operation:
·
Look ahead
·
Look again
·
Automatic look again and reset
The PMT circuit will not allow the control to start under the
following conditions:
·
The control monitors both armature and field FET's at
start-up and during running.
·
The control will not allow the line contactor to close at
start-up, or will drop it out during running, if either the
armature or field FET's are defective, so as to cause
uncontrolled truck movement.
Section 2.2.4 Thermal Protector (TP)
This temperature sensitive device is internal to the power
transistor (Q1) module. If the transistor's temperature
begins to exceed the design limits, the thermal protector
will lower the maximum current limit, and maintain the
transistors within their temperature limits. Even at a
reduced current limit, the vehicle will normally be able to
reach sufficient speed to initiate 1A operation, thereby
allowing the control to cool. As the control cools, the
thermal protector will automatically reset, returning the
control to full power.
Section 2.2.5 Low Voltage
Batteries under load, particularly if undersized or more
than 80 percent discharged, will produce low voltages at
the control terminals. The SX control is designed for use
down to 50 percent of a nominal battery voltage of 36-84
volts, and 75 percent of a nominal battery voltage of 24
volts. Lower battery voltage may cause the control to
operate improperly, however, the resulting PMT should
open the Line contactor, in the event of a failure.
