28 volt 1981 Aztec. I thought my bus voltage was a bit high. Consulted the MM for the setting / checking procedure (Lamar over volt and VR) and had my IA do the magic stuff to parallel them and set them to 28.5 volts.
Interesting that while he was setting the 28.5 volts at the VR I was reading 29.5 volts on the JPI EDM 960. Used a different voltmeter to confirm the 28.5 at the VR. Confirmed. Cockpit instrument continued to show 29.5.
Did a short test flight. The JPI said 29.6 volts with both halves of the Master ON (29.6 left only and 29.5 right only). Downloaded the EDM and it confirmed the 29.6.Put the plane away connected to the BatteryMinder. In the morning the Minder was in the float mode. Disconnected the Minder AND the battery. Came back 6 hours later and the OCV was 26.0. Connected the battery and the voltage on the JPI showed 25.1. Turned off one half of the master switch (Alt field) and volts increased to 25.25. Switch back on and turned off the other half - same 25.25v.
Connected a third voltmeter directly to the bus at the JPI Display C.B. location and to airframe ground: 25.1 volts.
From the above I conclude that [a] the JPI reading is accurate; I'm getting 29.5 volts on the bus even though the VR's are set to 28.5; [c] the combination of the Master Solenoid / EDM Display / one EDM DAU causes a 1 volt drop on the bus compared to the disconnected battery (OCV).
Connections go Bus to VR C.B. to Master switch(s) to Alternator switches (I think ~ mechanical connection? - PF3 and PF4 respectively) to Overvolt relay to VR to Alternator to Shunt to Alternator C.B. to Bus.
Being skeptical of coincidental dual (L & R) failures, I'm at a loss regarding what the problem is or what the next step should be.
Thoughts or ideas? Suggestions? Thanks
Interesting that while he was setting the 28.5 volts at the VR I was reading 29.5 volts on the JPI EDM 960. Used a different voltmeter to confirm the 28.5 at the VR. Confirmed. Cockpit instrument continued to show 29.5.
Did a short test flight. The JPI said 29.6 volts with both halves of the Master ON (29.6 left only and 29.5 right only). Downloaded the EDM and it confirmed the 29.6.Put the plane away connected to the BatteryMinder. In the morning the Minder was in the float mode. Disconnected the Minder AND the battery. Came back 6 hours later and the OCV was 26.0. Connected the battery and the voltage on the JPI showed 25.1. Turned off one half of the master switch (Alt field) and volts increased to 25.25. Switch back on and turned off the other half - same 25.25v.
Connected a third voltmeter directly to the bus at the JPI Display C.B. location and to airframe ground: 25.1 volts.
From the above I conclude that [a] the JPI reading is accurate; I'm getting 29.5 volts on the bus even though the VR's are set to 28.5; [c] the combination of the Master Solenoid / EDM Display / one EDM DAU causes a 1 volt drop on the bus compared to the disconnected battery (OCV).
Connections go Bus to VR C.B. to Master switch(s) to Alternator switches (I think ~ mechanical connection? - PF3 and PF4 respectively) to Overvolt relay to VR to Alternator to Shunt to Alternator C.B. to Bus.
Being skeptical of coincidental dual (L & R) failures, I'm at a loss regarding what the problem is or what the next step should be.
Thoughts or ideas? Suggestions? Thanks
