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Page Title: ACCELERATION TIME.
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NOTE
c.
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.
c.
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.
b.
Adjustment is made for feel of operation.
6-51

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