FIELD WEAKENING ADJUSTMENT.

(5)

Repeat steps above until drop-out is

6-244. FIELD WEAKENING ADJUSTMENT.

correct.

a. Field weakening provides for maximum truck

speed and is controlled through the shorting contactor

(6) Again accelerate until the SC and FW

SC relay (17, figure 7-3).

relays close and gently apply brake until FW relay drops

out.

b. Field weakening relay is adjusted to operate at

the following amperes:

(7) Gradually release brake until the FW relay

picks up and note current draw on ammeter.

(1)

Relay

closes

(pick-up)

125

150

amperes.

(8) If not 125 to 150 amperes, release both

brake and accelerator.

(2)

Relay opens (drops out) 350 to 365

amperes.

(9) Adjust field weakening pack pick-up

trimmer (figure 6-2) similar to (4) above.

Adjust or pick-up and drop-out as follows:

CAUTION

(1) With direction control in forward direction,

depress accelerator pedal slowly until two clicks of the

Avoid excessive operation of loading motor by

shorting contactor SC (17) and the field weakening FW

applying service brakes with the brake switch

(19) relays are heard or the contacts are seen to close.

jumped. This will cause extreme motor heat

Hold this accelerator position.

and excessive wear of brake lining.

(2) Gently apply fool service brake while

6-245. CURRENT LIMIT ADJUSTMENT.

holding motor speed until the field weakening relay

a. The current limit prevents excess current from

drops out. Note current draw on ammeter.

damaging the system. The limit must be adjusted when

changing from a lead-acid to a nickel-iron alkaline

(3) If not 350 to 365 amperes, release both

battery. See para 6251.

brake and accelerator.

b. The current limit must be adjusted to a

(4) Adjust field weakening pack (20) drop-out

maximum of 200 amperes.

trimmer (figure (-2). Loosen locknut and turn clockwise

to decrease current draw. Lock locknut.

Figure 6-2. Electrical Control Trimmer Locations

6-50