Narrative:

Approximately 58 mins after takeoff the battery charger light illuminated. The abnormal procedure was accomplished. However, the light would not extinguish. The checklist required me to land at the nearest suitable airport and contact dispatch. I coordinated with ZZZ dispatch and diverted flight to tpa. While informing the #1 flight attendant of the problem, he told me he had heard a loud bang coming from the floor below the first class galley. Realizing the severity of our electrical problem and not having any knowledge of what caused the loud bang, I declared an emergency. The bang was heard twice more by the first officer and the #1 flight attendant. Flight landed uneventfully at tpa and we were visually checked by the tpa arrf personnel. Aircraft was taken OTS and flight was delayed until new equipment arrived. We continued to dfw arriving at XA10 local. Callback conversation with reporter revealed the following information: the reporter stated the cause of the battery fail light to illuminate was the charger cooling fan had failed and the charger thermal overheat protection shut it down. The reporter said as for the 3 bangs or thumps these were caused by a 'round' relay being activated. The reporter stated the maintenance people call it a 'round' relay but never explained its function and why its called 'round.'

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Original NASA ASRS Text

Title: AN MD80 IN CRUISE AT FL310 DECLARED AN EMER AND DIVERTED DUE TO THE BATTERY CHARGER FAIL LIGHT ILLUMINATED AND UNUSUAL BANG OR NOISE UNDER THE GALLEY FLOOR.

Narrative: APPROX 58 MINS AFTER TKOF THE BATTERY CHARGER LIGHT ILLUMINATED. THE ABNORMAL PROC WAS ACCOMPLISHED. HOWEVER, THE LIGHT WOULD NOT EXTINGUISH. THE CHKLIST REQUIRED ME TO LAND AT THE NEAREST SUITABLE ARPT AND CONTACT DISPATCH. I COORDINATED WITH ZZZ DISPATCH AND DIVERTED FLT TO TPA. WHILE INFORMING THE #1 FLT ATTENDANT OF THE PROB, HE TOLD ME HE HAD HEARD A LOUD BANG COMING FROM THE FLOOR BELOW THE FIRST CLASS GALLEY. REALIZING THE SEVERITY OF OUR ELECTRICAL PROB AND NOT HAVING ANY KNOWLEDGE OF WHAT CAUSED THE LOUD BANG, I DECLARED AN EMER. THE BANG WAS HEARD TWICE MORE BY THE FO AND THE #1 FLT ATTENDANT. FLT LANDED UNEVENTFULLY AT TPA AND WE WERE VISUALLY CHKED BY THE TPA ARRF PERSONNEL. ACFT WAS TAKEN OTS AND FLT WAS DELAYED UNTIL NEW EQUIP ARRIVED. WE CONTINUED TO DFW ARRIVING AT XA10 LCL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE BATTERY FAIL LIGHT TO ILLUMINATE WAS THE CHARGER COOLING FAN HAD FAILED AND THE CHARGER THERMAL OVERHEAT PROTECTION SHUT IT DOWN. THE RPTR SAID AS FOR THE 3 BANGS OR THUMPS THESE WERE CAUSED BY A 'ROUND' RELAY BEING ACTIVATED. THE RPTR STATED THE MAINT PEOPLE CALL IT A 'ROUND' RELAY BUT NEVER EXPLAINED ITS FUNCTION AND WHY ITS CALLED 'ROUND.'

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.