GE IC3645SP4U400N3 b Creep Speed, c Control Acceleration, Current Limit, d Auto Braking

BASIC OPERATION AND FEATURES

SX TRANSISTOR CONTROL Page 6

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

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 percent on-time has a range of approximately 0 to 100 percent. The SX controllers operate at a constant frequency and the percent on-time is controlled by the pulse width of the voltage / current applied to the motor circuits.

Section 2.1.1.b Creep Speed

With the accelerator at maximum ohms or volts (approximately 3.7 to 3.5 VDC), the creep speed can be adjusted by Function 2 of the Handset. At creep speed, the ON time can decrease to approximately 5%, with the OFF time at approximately 95%. At full transistor operation, this condition will be reversed (short OFF time, long ON time). This variation of ON and OFF time of the oscillator varies the voltage applied to the motor, thereby varying the speed of the motor for a given load.

Section 2.1.1.c 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 pre-set 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 Braking

Section 2.1.3.a Plug Braking

Section 2.1.3.b Regenerative Braking to Zero Speed

		Slow down is accomplished when
		reversing direction by providing a
		small amount of retarding torque for
Q2		deceleration. If the vehicle is
	ARM moving, and the directional lever is
		moved from one direction to the
		other, the regen signal is initiated.
	Q1	Once the regen signal has been
		initiated, the field current is
Figure 5		increased (armature circuit shown in
		Figure 5). Armature current is

regulated to the regen current limit as set by Function 9. As the vehicle slows down, the field current continues to increase, and transistor Q2 begins to chop. The field current will increase until it reaches a preset value set by Function 10, and transistor Q2 on-time will increase until it reaches 100% on-time. Once both of the above conditions have been met, and regen current limit can no longer be maintained, the braking function is canceled. The fields will then reverse, and the control reverts back to motoring. Part of the energy produced by the motor during regen is returned to the battery, and part is dumped in the motor as heat.

Section 2.1.3.c Pedal Position Plug Braking

This feature allows control of the plugging distance based on pedal position when there has been a “directional switch" change. Pedal position will reduce the regenerative current to the "value set by this function" as the accelerator is returned to the creep speed position. Maximum regen current is obtained with the accelerator in the top speed position.

Section 2.1.3.d Auto Braking

This feature is enabled by initiating a "neutral position" using either the directional switch or the accelerator switch. Once activated, Auto Braking operates similar to Pedal Position Plug Braking and is adjusted by using Function 21 of the Handset.

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 and the accelerator input voltage is less than 1 volt. It is important to note that this function is used

January 2000