A high-volume distribution center experienced a frustrating, intermittent failure on a Raymond 9600 stand-up reach truck. The truck operated perfectly on flat aisles, but when traveling up a 5% grade ramp with a load, the drive motor would suddenly cut out completely. The operator would have to wait a few seconds, cycle the key, and the truck would drive again. This was severely impacting productivity in the multi-level racking system.
The Raymond 9600 uses a 36-volt AC traction system controlled by a Sevcon Gen4 controller. Because the fault occurred under heavy load on an incline, the technician suspected a voltage drop triggering a controller undervoltage fault. A multimeter was connected directly to the controller's B+ and B- bus bars. While driving on flat ground, the voltage read a steady 37.2V. However, the moment the truck hit the incline and the controller demanded high amperage from the battery, the voltage at the controller plummeted to 22 volts, instantly triggering the low-voltage lockout and killing the drive.
The massive 15-volt drop between the battery and the controller indicated severe high resistance in the main power circuit. The technician bypassed the battery cables with heavy-duty jumper cables directly from the battery terminals to the controller bus bars; the truck then climbed the ramp flawlessly, confirming the cables or connectors were the issue.
Inspection of the battery connector (an SB175 style plug) revealed the root cause. The male and female contact pins inside the connector were heavily discolored, showing a blue-black tint consistent with extreme heat. Over time, the spring tension in the female pins had relaxed, creating a loose fit. When high current was drawn on the ramp, the resistance across the loose pins generated intense heat, which further increased electrical resistance, causing the voltage to crash.
Furthermore, the main 1A contactor (the main power relay for the drive system) was inspected. The contact tips were severely pitted and carbon-tracked. The low voltage at the battery connector meant the contactor coil was not receiving enough voltage to keep the contacts pulled in tightly, causing them to chatter and arc under load, which accelerated the pitting.
The repair involved cutting off the burnt battery connectors and crimping on a brand-new SB175 connector kit with fresh, high-tension contact pins. The main 1A contactor was replaced. Finally, the battery terminals themselves were cleaned and coated with anti-oxidant grease. On the next ramp test, the voltage at the controller only dropped to 34 volts under load, and the reach truck climbed smoothly without a single traction cutout.
