A logistics warehouse reported that a Jungheinrich ETV 320 reach truck would suddenly stop (cut power) after 20 minutes of continuous driving. The fault code indicated "Motor Overtemperature."
The technician inspected the "Traction Motor" (a series-wound DC motor located under the seat). The motor housing was very hot. He checked the "Cooling Fan" mounted on the motor shaft. The fan was spinning, but the "Intake Screen" on the motor housing was clogged with packaging plastic wrap. This blocked the airflow, causing the motor to retain heat.
He then removed the motor "Inspection Band" to check the brushes. The "Brush Springs" (which hold the brushes against the commutator) were weak. The weak springs caused "Brush Bouncing." The brushes intermittently lost contact with the commutator, causing "Electrical Arcing" (sparks). The arcing generated high heat at the commutator bars, in addition to the blocked airflow.
The repair involved cleaning the intake screen and motor housing with compressed air. The brush springs were replaced with new tension springs. The commutator surface was lightly sanded with "Commutator Stone" (a specialized abrasive) to remove the carbon buildup and pits from arcing. The motor was reassembled. The reach truck then ran for 2 hours without tripping the thermal switch.
