Unregulated Voltage

The following information is derived from the FAA's Service Difficulty Reports and Aviation Maintenance Alerts.


Cessna 172M Skyhawk

Burned Voltage Regulator

The pilot reported an odor of smoke in the cockpit and returned to the departure airport. Examination revealed electrical charging system inoperative. Replaced voltage regulator (p/n VR6000).

Part total time: Unknown

Cessna 172P Skyhawk

Unserviceable Regulator

Technician suspects the voltage regulator (p/n DG3) went unsatisfactory and allowed the full alternator output to overcharge the system, shorting out the main alternator circuit breaker and causing smoke in the cockpit.

Part total time: 805.0 hours

Cessna 402C Utiliner/Businessliner

Damaged Voltage Regulator

The pilot reported a dual alternator failure after takeoff. Maintenance inspected and found the right-hand voltage regulator (p/n 99101263) was defective. This was replaced and paralleled. No further defects noted.

Part total time: 4814.0 hours

Cessna 402C Utiliner/Businessliner

Loose Alternator Fuse

Pilot reported both alternators dropped off line and a smoke odor was noted in the cockpit before diverting and landing safely. Upon inspection, initially suspected over-voltage relay shorting against panel but in-flight checks revealed the problem recurred after several minutes of flight. Upon further inspection, an alternator field fuse was found loose in its housing. After correction, the aircraft operated normally during check flight.

Part total time: Unknown

Piper PA-28-180 Cherokee 180

Internal Over-Voltage Relay

The customer complained the alternator (p/n R1224) would quit charging after approximately a 20-minute flight. Test flight confirmed observation. Replaced voltage regulator with new unit, performed test flight and system functioned normally. Technician suspects the internal over-voltage relay was tripping at too low a voltage, perhaps related to heat.

Part total time: 19.0 hours

Piper PA-31-350 Navajo Chieftain

Shorted Voltage Regulator

On climbout, the pilot reported the left alternator output went to zero and the right alternator warning light illuminated. Resetting took both alternators off-line; resetting only the right alternator worked and the pilot returned to the departure airport, landing without incident. Troubleshooting determined the left voltage regulator (p/n B-00286-1) was the source of the fault. Replaced the left voltage regulator; ground check was normal.

Part total time: Unknown


Please enter your comment!
Please enter your name here