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Electrical System with TX and TT Card
PS
S5.0
5000
F-code
Section
C-code
Version no
T-code
001
OE35
© BT Products
135
Service Manual
1997-10-23
3. Basics Of Circuit Operation
The control circuit is energized by closing the key switch,
pushing start button, closing foot pedal switch (which closes
brake interlock switch), and rotating direction control to either
forward or rearward direction. Rotating the direction controls
closes forward and rearward direction switches and positions
the accelerator potentiometer which controls the speed of the
truck. This applies electrical power to the control card turning
on the card internal PMT driver, which will close the selected
directional contactor and complete the circuits to the drive
motor.
The control card then supplies a gate pulse to 2REC turning it
on to a conducting state, allowing current to flow from the
battery through 1C, 1X, 2REC, motor field, motor armature,
sensor, and back to the battery. After 1C charges, 2REC
shuts off due to lack of holding current. The control card
checks that 1C is charged and unlocks the gate to 1REC and
5REC.
The control card then supplies a gate pulse to 1REC turning it
on to a conducting state, allowing current to flow from the
battery through 1REC, motor field, motor armature, sensor,
and back to the battery. 5 REC turns on and allows current to
flow T4-T3, 1C, 1REC, 5 REC to T4-T3. This current charges
the bottom of 1C positive with respect to the battery positive
bus. This charging cycle occurs in less than 1 millisecond
(.001 sec.) and 5 REC shuts off. This charge is now stored on
the capacitor until it is time to turn off 1REC.
Current continues to flow in 1REC until the control card fires
2REC. When 2REC conducts, capacitor 1C discharges
around the circuit composed of 1C, 1X, 2REC, and 1REC.
This discharge current opposes the battery current through
1REC so that the resultant current is zero. With reverse
voltage across 1REC, 1REC is turned off. Current continues
to flow in the 2REC, 1C, motor and battery loop until the
capacitor (card terminal 14) is fully charged negative. This
charge exceeds battery voltage by an amount which is a
function of peak motor current, and 2REC turns off. The
illustrates below shows the pulsing of current from the
battery.
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