Motor controller failure caused by voltage spike during start-up on 12V battery
Test bench setup with a new brushless DC motor controller designed for 12V operation. Power source is a 12V lead‑acid battery. The controller includes an input filter capacitor rated for a maximum voltage of 12V. No additional surge protection or pre‑charge circuitry was present. The motor draws high inrush current at spin‑up.
During the initial spin‑up the controller emitted a loud pop and ceased functioning. Visual inspection showed burnt traces on the PCB and a ruptured input capacitor. The battery voltage remained at 12.6V before and after the test. No diagnostic LEDs lit after the event. Replacing the controller with a 24V‑rated version allowed the motor to start without immediate failure, but the user noted possible latency issues.
1. The controller’s input capacitor is specified for a maximum voltage of 12V. During motor start‑up the instantaneous current draw can cause a voltage overshoot due to the battery’s low internal resistance. 2. The overshoot can exceed the capacitor’s voltage rating, leading to dielectric breakdown and catastrophic failure, which matches the observed burnt capacitor and popped sound. 3. Swapping to a 24V‑rated controller increased the voltage margin of the input capacitor, preventing immediate breakdown, which explains why the motor now starts successfully. 4. However, the 24V controller may have a slower PWM response or higher gate drive impedance, which could introduce latency in torque control. 5. The root cause is therefore insufficient voltage headroom on the input filter component, not the controller’s voltage rating itself.