The PB-2 is designed to work with controllers that have a 3-wire input, but can also be used with controllers with only a 2-wire input.
· Same physical shape as the PB-6, as well as the same mounting pattern
· 3 terminal safety microswitch which may be used for various control inputs
· Stainless steel case with spring return lever
· Output: 0 - 5K ohm
The standard controller throttle input is 0–5kO. Curtis potboxes (PB-5, -6/8, -9, -10) are designed to match this input. Some of these potboxes have a built-in safety microswitch, eliminating the need to install a separate pedal-actuated safety microswitch. Curtis also offers a self-contained foot pedal unit (FP-2) that eliminates the need for fabricating and installing a pedal-potbox linkage. Any potbox that provides a nominal 0–5kO output (controller output begins at 300 ohms, full output is 4400 ohms) will work with the standard throttle input.
The pot box must be mounted so as to allow connection between the potbox lever arm and the vehicle accelerator linkage. The mounting dimensions are shown in Figure 3. The lever arm provides a series of holes so that the accelerator pedal “throw” can be converted into the correct amount of potentiometer rotation. Use of a second return spring on the pedal, in addition to the potbox return spring, is required to prevent an uncontrollable full-on throttle input (which could happen if there was a single spring, and it broke). If the self-contained potbox spring is insufficient to return the pedal by itself, two additional pedal return springs must be used.
It is also required that the accelerator pedal hit a mechanical stop at its full-on position just before (1 mm [1/32"–1/16"]) the potbox lever hits its own full-on stop. This mechanical stop will prevent the potbox lever arm from bending if undue force is put on the pedal. Protection of the potbox from water and dirt will help avoid problems of corrosion and electrical leakage.
After the potbox has been mounted, operation of the pot can be tested by measuring the resistance between the two wires with an ohmmeter. With the pedal not applied, the resistance should be less than 50 ohms. As the pedal is applied, the resistance should rise smoothly until it reaches a value between 4500 and 5500 ohms. Values below 4500 ohms may cause a reduction in efficiency and top speed. Values above 7000 ohms indicate a defective potbox, and will cause controller shutdown.
Potbox maintenance is similar to controller maintenance: inspect for integrity of connections and mounting, and clean (with a moist rag) as required.
Curtis potboxes are factory set and rarely require user attention. To test and adjust, connect an ohmmeter to the potbox wires and use this procedure:
1. With the spring holding the lever arm against the return stop, the resistance should be less than 50 ohms. Slowly move the lever. If the resistance abruptly starts to increase when the lever is 3 mm (1/8") from the stop (1.5 mm [1/16"] for potboxes without the safety microswitch), no adjustment is needed.
2. If adjustment is required, loosen the screw holding the lever on the pot shaft. Use a screwdriver to rotate the pot shaft slightly with respect to the lever. Recheck the point at which the resistance starts to increase and continue making adjustments until the increase occurs at 3 mm (1/8") [at 1.5 mm (1/16") for potboxes without the safety microswitch]. When adjustment is correct, tighten the screw holding the lever on the pot shaft, then recheck to see that this action did not disturb the adjustment. Make sure that the lever is still seated down on the pot shaft below the slight bevel on the end of the shaft.
3. Check the resistance with the lever pushed all the way to the other stop. It should be between 4500 and 5500 ohms. If it is outside this range, the potbox is faulty and should be replaced.
4. For potboxes equipped with a safety microswitch, check for correct switch operation. Use an ohmmeter, or simply listen for the slight click the switch makes. It should operate when the lever is 1.5 mm (1/16") from the return stop. If it does not, adjust by loosening the two screws holding the slotted safety microswitch mounting plate to the stop spacers and moving the plate. Recheck the switch operating point after tightening the screws.
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