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I don't know that 12.3 volts indicates you have a problem. While charging the battery, the voltage should take a while to reach 14 volts like the red curve at this link:

https://wiki.xtronics.com/index.php/Sealed_Lead_Acid_Battery_Applications

Also, you might double check the bus voltage with a known good multimeter and compare it to what your EFIS reads. Mine is off by ~1.5 volts for some reason.

That being said, you should see some jump in voltage as the regulator starts charging the battery. Were you also reading 12.3 volts before starting the engine?

My voltage seems to take 20-30 minutes of flight to stabilize at a peak value. I don't know that I'd be able to draw many conclusions from running for a few minutes on the ground at 2000rpm.

On starting my Aerovee I will see 12.3 to 12.5 volts until I reach above 2500 rpm at take off and in cruise.I don't see the voltage come up for at least 20 min of flight. After an hour flight I see 13 to 13.5 volts so I know its fully recharged. I have never seen 14 volts on the MGL. It could be a calibration issue or just a quirk of the Aerovee. These alternators don't produce much energy at low rpm, really need to be above 2500 rpm to throw off much juice.

jwd3ca wrote:Installed new regulator. No joy. STILL seeing 12.3 @ 2000 rpm. Should be over 14 :( I have a dedicated case ground, so it's not a grounding issue. Guess I better re-measure AC from stator, but it was over 40VAC previously, not holding my breath on that. GRT EIS measures bus voltage, has no relevant settings that I am aware of...

I've never seen 14v on the ground. I only see 14 to 14.2 after being in cruise flight for a while. I can run the engine up on the ground to full throttle and I would never see anything even close to 14v, so I don't think measuring on the ground a low RPMs is telling you anything useful.

Encouraging words, guys. Maybe I'm expecting too much too soon :) Thanks for your input. I'll let you know as I prepare for the test flight.

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daleandee wrote:Hate to disagree with the others but you do have a problem. A fully charged 12 volt battery should read 12.6-12.8 volts before engine start. 12.3 volts shows the battery to be ~ 60% charged.

Yes, but you can get it back by putting it on the charger. The original question I thought, was whether there was something wrong if the voltage isn't showing 13.5-14.2V at 2,000 rpm, which it won't.

I went out flying this morning. On the ground it showed 13.1V before startup. Taxiing it was at 12.8. For the first 15 minutes flying it was 12.9. It wasn't until I'd been flying 30 minutes that it showed 13.9. Another 10 minutes before it showed 14.2. During decent and landing (lower RPM) it showed 13.2 down to 12.9. I turn off the secondary ignition (AeroVee) during taxi, and it shows 13.2. If I leave the secondary on it shows 12.7 to 12.9. This has been fairly typical for the past 2 years and 200 hours.