Plugging Potentiometer Adjustment

TM 10-3930-631-34

d. Adjust inching potentiometer to desired

tested, remove braided cathode lead of diodes (fig. 9-6)

from terminal studs to isolate the diodes. Use diode

performance or so lift truck inches along with

block as anode for testing D1 and D2 diodes.

accelerator pedal slightly depressed.

To adjust

b. The following ohmmeter test for a diode will

potentiometer, loosen locknut and turn inching

determine if it is blocking and in proper polarity. Touch

potentiometer shaft {fig. 9-3) clockwise to in- crease'

positive lead of multimeter to anode and negative lead to

inching or counterclockwise to decrease it.

After

cathode. Reading should be low resistance. Touch

adjustment is completed, hold potentiometer shaft in

positive lead to cathode and negative lead to anode.

place and tighten locknut to prevent shaft from turning

Reading should be infinity. If above reading are not

out of adjustment.

obtained, replace

9-14. Plugging Potentiometer Adjustment

diode (para. 9-28).

a. Slowdown is accomplished when a direction is

c. Whenever stud type D1 and D2 diodes are

reversed by providing a small amount of retarding

replaced, it is recommended that a heat transfer grease

torque for deceleration. If the lift truck is moving, the

(silicon compound, or an equivalent) is used between

accelerator pedal is released, the forward and reverse

the stud of the diode and the diode block. Diodes

lever is moved from forward to reverse, and the

should be screwed into the diode block and tightened to

accelerator pedal is then depressed again, the motor

a torque of 275-325 pound- inches (2.30-2.79 m-kg).

field is reversed. The distance or severity of the

d. The diodes can be checked further to assure

reversal is adjustable

by means of a plugging

the diode does not conduct current in the reverse

potentiometer.

direction of battery voltage.

b. After tests are completed and drive wheels are

e. Connect battery, a 10K ohm resistor, voltmeter

lowered to the floor, operate lift truck and plug it at full

and diode as illustrated in figure 9-9.

speed. If stopping distance is too short or too long,

adjust plugging potentiometer until desired stopping

distance is obtained.

c. Adjust the plugging with the plugging

potentiometer (fig. 9-3) located on the side of the

speed control box.

d. Loosen locknut just enough so potentiometer

shaft can be turned. Turn plugging potentiometer shaft

clockwise for a severe

plugging condition or

counterclockwise for a soft plugging condition. After

adjustment is completed, hold potentiometer shaft in

place and tighten locknut to prevent shaft from turning

out of adjustment.

CAUTION

Plugging is a performance adjustment. It can

be adjusted for a severe or soft plug and will not

harm the control. However, if it is set too

severe, damage to the drive motor or the drive

axle may result.

9-15. Dynamic Test

Figure 9-9. Diode Test.

a. Make certain the drive wheels are completely

clear of blocks and floor and the cardboard is removed

f. If diode is good, meter should read zero voltage.

from the contactors.

If reading shows a voltage, replace diode (para 9-28).

b. Sit on the operator's seat and turn the key

9-17. Diode Suppressor Module Test

switch to the ON position. Move the forward and

a. The diode suppressor module (fig. 9-10) is

reverse lever to forward. Depress the accelerator pedal

located in the upper portion of the contactor panel (fig.

slightly until the forward contactor closes.

2-7). To check the diode suppressor module, connect

c. Slowly continue to depress the accelerator pedal.

ohmmeter leads as indicated in the following table.

Wheels should begin to turn and pick up speed slowly

b. Meter reading is 20K initially and then indicator

and smoothly.

should move towards infinity.

9-16. D1 and D2 Diode Test

a. Disconnect

the

battery

and

discharge

capacitors. Before D1 free wheeling and D2 armature

diodes (located on the static panel) are

9-15