Date: 202008
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Weather elements / visibility: Haze / Smoke
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: Personal
Operating under: Part 91
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: DC Regulator
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Enroute ZZZ1 to ZZZ approximately 1.5 hours into flight in MVFR I began to get wildly oscillating readings from the voltage regulator ranging from 16.1v tp battery discharge (~12.4v). Resetting the alternator had no effect and voltage oscillations continued. I shut down all avionics except the transponder to conserve the battery and landed uneventfully at ZZZ. An A&P was located who inspected the electrical wiring (nothing adverse found); tested the alternator (tested OK); and cleaned the contacts at the voltage regulator. A test flight was made without incident. The following day I left ZZZ for ZZZ2 in MVFR (wildfire smoke) and at the 1.5 hour mark the voltage readings began the same wild oscillation as the day before. I shut down all avionics except the transponder and landed without incident at ZZZ3 where the voltage regulator contacts were again cleaned. A 3/4 power run up showed proper voltage (14.2v) and no oscillation. I continued the flight to ZZZ2 and after about 45 minutes the voltage oscillation returned. All avionics were shut down except the transponder. I fell back on the gyroscopic instruments; compass; and the IPad with Foreflight to safely navigate. Radios were turned back on for ZZZ2 and the flight completed. During the last 20 minutes of the flight with the avionics all back on there was no voltage oscillation. Inspection of the regulator (Zeftronics R15VOO Rev A) after shutdown shows no obvious defects but the regulator is obviously failing and a replacement regulator has been ordered.Lessons learned:-IFR partial panel skills should be kept current; even for VFR/MVFR flights.-MVFR/IFR flights should always have an independent navigation backup such as a Garmin or Foreflight/Stratus that can provide reliable navigation and weather information should the aircraft electrical system fail. This is particularly critical over mountainous terrain where landing options are more limited. -Just because an A&P says something is fixed; don't bet the farm on it. I altered the route to ensure that I was never more than 30 minutes (I estimated I had this much time partial panel with a discharging battery) from an airfield.-always know exactly how much draw every item in your panel has and what your total battery capacity is.




Synopsis: Pilot reported that the voltage regulator continued to show large oscillations mid-flight despite multiple efforts to isolate and solve the problem.