
BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL Page 5
August 2001
Section 2. FEATURES OF SX FAMILYOF TRANSISTOR
MOTOR CONTROLLERS
Section 2.1 Performance
Section 2.1.1 Oscillator Card Features
Section 2.1.1.a Standard Operation
The oscillator section of thecard has two adjustable
features, creep speed and minimum field current. With the
accelerator at maximum ohms or volts, the creep speed
can be adjusted by Function 2 of theHandset or a trimpot.
The field control section allows the adjustmentof the field
weakening level in order to set thetop speed of the motor.
This top speed function (Minimum Field Current) is enabled
when the armature current is less than the value set by
Function 24 and the accelerator inputvoltage is less than 1
volt. Top Speed can beadjusted by Function 7 of the
Handset or a trimpot.
The % ON-time has a range of approximately 0 to 100
percent. The SX controllers operate at a constant
frequency and the% ON-time is controlled by the pulse
width ofthe voltage/current applied to themotor circuits.
Section 2.1.1.b Control Acceleration
This feature allows for adjustment of the rate of time it
takes for the control to accelerate to 100% applied battery
voltage to themotor on hard acceleration. ArmatureC/A is
adjusted by Function 3 from 0.1 to 22 seconds.
Section 2.1.2 Current Limit
This circuit monitors motor current by utilizing sensors in
series with the armature and field windings. The
information detected by the sensor is fed backto the card
so that current may be limited to a preset value. Ifheavy
load currents are detected, this circuitoverrides the
oscillator and limits the average currentto a value set by
Function 4 and Function 8 of the Handset. TheC/L setting is
based on the maximum thermal rating of the control.
Because of the flyback current through 3REC, the motor
current isusually greater than battery current, except at
100% ON time.
Section 2.1.3 Plug Braking
Slow down is accomplished when reversing direction by
providing a small amount of retarding torque for
deceleration. If the vehicle is moving, and the directional
lever ismoved from one direction to theother, the plug
signal is initiated. Once the plug signal has been initiated,
the field is reversed, and the armature current is regulated
to the plug current limitas set by Function 16. Armature
current is regulated by increasing the field current as the
vehicle slows down. Once the field current reaches a
preset value, set by Function 10, and armature plug current
can no longer be maintained, the braking function is
canceled, and the control reverts back to motoring.
All energy produced by themotor during plugging is
dumped as heatin the motor in this braking mode.
Section 2.1.4 Auxiliary Speed Control
Section 2.1.4.a Field Weakening
This function allows the adjustmentof the field weakening
level in order to set the top speed of the motor. The function
is enabled when the armature current is less than the value
set by Function 24 and the accelerator input voltage isless
than 1 volt. It is important to note that this function is used
to optimizemotor 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 withoutthe permission ofthe OEM.
Section 2.1.4.b Speed Limits
This feature provides a means to control speed by limiting
motor volts utilizing "adjustable speed limits", initiated by
individual limit switches. The NC switches areconnected
between input points on the control card and battery
negative. The lower motor volt limit always takes priority
when morethan one switch input is open. 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.
Section 2.1.4.c Top Speed Regulation
This feature requires a system tachometer. The standard
GE system tach is built into the motor and provides four
pulses per armaturerevolution. Once the control has been
calibrated to the vehicleparameters (gear ratio
and wheel rolling radius), using Function 1, speed can be
measured with a resolution of +/- 1 mph. When traveling
down an incline, if the vehicle speed increases to the
overspeed setting, the control automatically transitions to
the regen mode. The maximum incline on which the control
will be able to maintain regulation is determined by the
characteristics of the motor, the maximum regen armature
current limit setting (Function 9), and themaximum regen
field currentlimit setting (Function 10).
When the vehicle reaches the bottom of the incline, and
the vehicle speed decreases below the overspeed setting
on the level surface, the control automatically transitions
back to the normal running mode.