BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
Page 5
July 2001
Section 2. FEATURES OF SX FAMILY OF 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 the card 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 the Handset or a trimpot.
The field control section allows the adjustment of the field
weakening level in order to set the top 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 input voltage is less than 1
volt. Top Speed can be adjusted 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 of the voltage/current applied to the motor 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 the motor on hard acceleration. Armature C/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 back to the card
so that current may be limited to a preset value. If heavy
load currents are detected, this circuit overrides the
oscillator and limits the average current to a value set by
Function 4 and Function 8 of the Handset. The C/L setting is
based on the maximum thermal rating of the control.
Because of the flyback current through 3REC, the motor
current is usually 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 is moved from one direction to the other, 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 limit. 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 the motor during plugging is
dumped as heat in the motor in this braking mode.
Section 2.1.4 Auxiliary Speed Control
Section 2.1.4.a Field Weakening
This function allows the adjustment of 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. 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 limit motor speed by
controlling the armature voltage. The speed limit setting
provides a clamp on the accelerator voltage command,
limiting the conduction period of the armature FET’s.
There are two speed limit settings, reverse speed limit and
turf speed limit. When the reverse direction is selected, pin
5 is high, and the reverse speed limit will be used and the
turf switch is not checked by software. When the forward
direction is selected, pin 4 is high. The turf speed limit will
be enabled if the turf speed switch input, pin 6, is low.
The voltage to the motor armature will vary as a function of
the speed limit settings and the battery volts. The motor
speed will vary as a function of load and battery volts.
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 armature revolution. Once the control has been
calibrated to the vehicle parameters (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 over
speed 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 the maximum regen
field current limit setting (Function 10).
When the vehicle reaches the bottom of the incline, and the
vehicle speed decreases below the over speed setting on
