Figure 9-4. Control cycles.

TM 10-3930-631-34

through the power fuse, the now closed normally open

forward contacts (forward direction selected), S2 and S1

motor field terminals, normally closed reverse contacts,

and A1 and A2 drive motor armature terminals to the A2

terminal stud of the static panel. From A2 terminal stud,

current flows to the A2 terminals of the power switch

modules.

Load current leaves the

power switch

modules from terminal B- to the static panel B- terminal

stud; from there it flows back to the negative side of the

battery.

d. Basic Power Circuit with Free Wheeling Diode.

During the off time of each pulse, induced current from

the field windings flows to Al terminal of the drive motor

armature. Current leaves motor A2 terminal and flows

to the A2 terminal stud of the static panel. From there it

flows through D1 free wheeling diode, the B + static

panel terminal stud, and back through the

motor field in the proper direction.

e. Forward and Reverse Control Circuit.

(1) When the battery is connected and the key

switch, emergency cutout switch and seat switch are

Figure 9-4. Control cycles.

closed, the control circuit module will energize. Current

flow is from the positive side of the battery through the

(2) To provide smooth motor operation, the on-

power fuse and F2 16 amp control fuse to terminal P5-8

off cycle of the system is kept very short. Cycle times in

of the contactor panel. Current flow continues from

the order of milliseconds are used. Mechanical switches

terminal P6-8 through S1 key switch, S2 seat switch,

cannot accomplish this fast

switching; however,

and terminal P2-7 of plug P2 on the static panel to

transistors offer very efficient high speed switching.

terminal P1-22 of the control circuit module. The current

(3) Transistors in the system are turned on and

path continues out of control circuit module terminal P1-

off to convert the steady power from the battery into

18 through the capacitor B- bus bar to the B-terminal of

pulses that are supplied to the drive motor at a rate of

the static panel, and from there back to the negative

300 pulses per second. The on time of the transistors

side of the battery.

can be varied from zero to maximum. This variable on

(2) With a forward direction selected, current

time controls the motor speed. At slow speeds the on

flows from the closed key switch (S1-2) through the

time is very short. Increasing the on time through the

directional switch to terminal P5-12 of the contactor

range increases the motor speed until at high speed the

panel. In the contactor panel, the path is from terminal

on time is the full duration of the cycle.

P5-12 through the normally closed reverse interlock

(4) The on time of the transistors in the power

contacts, the forward contactor coil, contactor panel

switch module (fig. 9-2) is varied by the speed control

terminal P5-6, and terminal P2-6 of plug P2 on the static

which causes the control circuit module to turn the

panel to terminal P1-6 of the control circuit module.

transistors on and off.

Note

(5) During the off time of the control circuit

The directional interlock contacts are physically

module, induced motor current is allowed to flow

mounted on the forward and reverse contactors

through the motor in the proper direction. This current

and are mechanically operated whenever the

flow is through the free wheeling diode. The armature

applicable contactor closes or opens. The

diode allows rapid reversals of the directional selector

forward interlock contacts are mounted on the

and prevents the motor from acting as series generator.

forward contactor and the reverse interlock

(6) The forward and reverse switch deter-

contacts are mounted on the reverse contactor.

mines the path of current flow through the motor field to

(3) The current path continues out terminal P1-

provide the desired directional travel.

18 of the control circuit module, through the B- terminal

c. Drive Power Circuit. Current flow during the on

of the static panel, and back to the negative side of the

time is from the positive side of the battery

battery.

(4) When the forward coil is de-energized,

9-6