ACCELERATION TIME.

NOTE

Adjust the current limit as follows:

(1) Prepare truck according to para 6-243.

Truck may reach maximum SCR controlled

speed prior to covering 22 feet.

(2) Disconnect wire No. S from the No. 5

(2) Run test several times to get accurate

terminal of the anti-rollback pack ARP (12, figure 7-3).

reading if necessary.

(3) With direction control in forward position,

(3) To reduce time to cover 22 feet, faster

depress accelerator fully until maximum speed is

acceleration, rotate SCR control pack No. 2RH trimmer

obtained and hold position.

(figure 6-2) counterclockwise.

(4) Gently apply foot service brake until drive

(4) To increase time, slower acceleration,

motor stalls. Note current draw on ammeter.

rotate trimmer clockwise.

(5) If reading is not 200 amperes, adjust the

(5) Reconnect wire No. 5 to the No. 5

SCR control pack No.

4RH trimmer (figure 6-2)

terminal of the anti-rollback pack (1 2, figure 7-3)

clockwise to increase amperes to 200 or

removed in para 6-245.

counterclockwise to decrease limit.

6-248. SHORTING CONTACTOR TIME DELAY.

(6) Repeat steps 3, 4 and 5 above until

a. The shorting contactor timing delay is required

correct setting is obtained.

to provide a fraction of a second delay between the

point of maximum SCR speed control range and when

(7) Remove ammeter and shunt. Connect

the circuitry switches to the field weakening pack for

cable removed in para 6-243(4). Remove brake switch

maximum speed. The shorting contactor also cuts out

jumper and connect plugs. Attach floor.

tile SCR controlled acceleration.

6-246. CREEP SPEED. Adjust as follows:

b. The shorting contactor relay (l17, figure 7-3) is

(1) Place direction control in either forward or

adjusted to close in approximately the same time that

reverse position and lightly depress accelerator until

was established for acceleration time (para 6-247).

forward or reverse relays (I8, figure 7-3)just close.

NOTE

(2) If truck falls to move on level floor, adjust

For smooth operation of truck, the shorting

the SCR control pack No. 1 Rh trimmer (figure 62)

contactor time delay should never be set to a

clockwise until truck begins to move.

value less than tile acceleration time.

c. Adjust time delay as follows:

(3) If truck moves too fast, adjust trimmer

(1) Rotate SCR control pack No.

3RII

counterclockwise.

trimmer (figure 6-2) fully clockwise until the screw slips.

6-247. ACCELERATION TIME.

(2) Operate truck full speed forward and

a. The acceleration time is that time required for

observe when shorting contactor closes. The relay will

the truck to progress in speed from a standstill to the

snap with a loud snap, followed immediately by the field

maximum SCR controlled speed.

weakening relay pick-up.

NOTE

(3) Rotate trimmer counterclockwise in small

The maximum unloaded forward speed is 5.8

steps and repeat (2) above.

mph when the shorting contactor and field

weakening pack are connected.

(4) Continue adjusting until shorting contactor

b. Acceleration time is adjusted to provide 22 feet

relay closes in approximately the same time that was

of forward movement from standstill in 6 seconds.

derived in the acceleration time adjustment.

Adjust acceleration rate as follows:

6-249. PLUGGING SEVERITY.

(1) Using a watch with a sweep second hand

a. Plugging is the act of switching the direction

or stop watch, accurately time the time required to travel

control while moving in one direction at maximum speed

22 feet. From standstill with direction control in forward

without use of the service brakes. In plugging, the

position, depress accelerator fully.

motor will act as a braking force.

Adjustment is made for feel of operation.

6-51