Short-circuit on AC output results in current transformer burden resistor failure.

[kyang014]

During testing, I induced a short circuit on AC output of a OpenEVSE Advanced kit with controller hardware V5. The upstream circuit breaker tripped, but the event appears to have caused R26 to fail open. On subsequent charge attempts, the sensed current value was 100A+ despite the real current being 16A. Overcurrent faults were thrown as a result and charging stopped.

The current transformer itself tested normal and output a voltage corresponding to the correct 16A when measured out-of-circuit with a known good burden resistor. The 2.5V divider on the controller was also working.

The controller operates normally when R26 was replaced. Presumably, the spike of current through the CT during the short circuit induced a high voltage across the CT output. Suggest clamping the voltage across R26 to protect both it and the ATMEGA.

[kyang014]

Potentially could be reproduced by using a bench power supply to apply a pulse of current to a wire wound around the CT many times to multiply the sensed current.