slightly high voltage on last flight

[JimmyV]

In my 90 hr FX2 with 363i FP, while flying yesterday got borderline high voltage on battery 2 ( ignition backup ) up to 15.0 to 15.1 volts in flight setting of yellow alarm which must be set at 14.9. The Earth X house battery was reading slightly higher than usual in the 14.6-14.7 volt range, but still in the green. When reviewing earlier engine data, and from my recollection both battery 1 and battery 2 tend to be solidly in the 14.1-14.2 volt range when in flight. Any thoughts on this? I looked at connections to the alternator, wondering if ground could be loose, but all seems secure. Ive done no multimeter investigations. Prior Carbon Cubs i've had all run consistently in the low 14 volt range. Are these slightly higher readings any cause for concern? Thanks.

[Andy]

"Are these slightly higher readings any cause for concern?"

15.1 V at the emergency ignition battery is not "slightly higher" than the normal approx 14.2 V value. I would consider it to be a serious over voltage condition that demands immediate attention.

About the only thing that can cause the battery voltages to be higher than normal is a failing alternator voltage regulator. The regulator is built into the Denso alternator. If I had this problem I'd test and/or change the alternator before anything else is damaged.

[Andy]

This regulator is listed as applicable to the Denso 021080-0760 alternator:

https://tinyurl.com/zedbsa5r

I'd call to verify before ordering.

[JimmyV]

This regulator is listed as applicable to the Denso 021080-0760 alternator:

https://tinyurl.com/zedbsa5r

I'd call to verify before ordering.

Thanks Andy! appreciate it.

[JimmyV]

took the alternator off and had it tested. The alternator shop felt the alternator functioning normally? Hmm.
Pete Dougherty is trouble shooting.

[Andy]

took the alternator off and had it tested. The alternator shop felt the alternator functioning normally? Hmm.
Pete Dougherty is trouble shooting.

Did they provide a test report? If so, what were the loaded and unloaded output voltages?

I have data logs from several different FX-3 and 14.1-14.3 seems typical for MAIN bus Volts. However, the regulator I linked earlier shows a set point of 14.5 V. It may not be a genuine Denso part.

With 15.1 V on the emergency ignition battery it will likely be charging with excessive current and its useful life may be reduced. The EarthX internal battery management system will probably protect it.

Do your data logs show a slow, or sudden, increase from the 14.1-14.2 V that had been normal for your aircraft?

[JimmyV]

Did they provide a test report? If so, what were the loaded and unloaded output voltages?

I have data logs from several different FX-3 and 14.1-14.3 seems typical for MAIN bus Volts. However, the regulator I linked earlier shows a set point of 14.5 V. It may not be a genuine Denso part.

With 15.1 V on the emergency ignition battery it will likely be charging with excessive current and its useful life may be reduced. The EarthX internal battery management system will probably protect it.

Do your data logs show a slow, or sudden, increase from the 14.1-14.2 V that had been normal for your aircraft?

No report on alternator test. Going back to mid October, looks like both voltages had been creeping upward, prior all at 14.1-14.2. Mid October 14.5 or so, seems more like a gradual increase over past several weeks until now.

[Andy]

It's possible this is an instrumention error. It seems strange that the ignition battery voltage is higher than main bus voltage. It should be a few tenths lower when charging because of the isolation diode voltage drop. However, I doubt the indicated voltages are more accurate than +/- 0.5 V with everything working correctly.

May be time for independent measurements with your multimeter.

[JimmyV]

ok, bit the bullet and just replaced the alternator with OEM brand new replacement, thinking the only source of high voltage had to be coming from an errant voltage regulator/alternator and at first today when going for short test flight, voltages stayed 14.2-14.3 range, then about 10-15 minutes into flight the voltages began to climb, 14.6 to 14.7 range ( again battery2 voltage ended up surpassing battery1 voltage by .1 volts, which ive never seen before until this issue began acting up). Im wondering if it could be an alternator grounding problem. I dont fully understand the alternator noise suppression, but the ground to the alternator is attached there and on to the block if i recall correctly. Any thoughts on doing a ground bypass leaving out the noise suppressor. Multimeter testing while the engine is running would be difficult at best. I have compared main bus voltage on the ground, not running, to the cigarette socket wired directly to the house battery, and they are spot on, so at least with engine not running they are the same. As expected the weather has been perfect!

[Andy]

It still sounds like an instrumentation error. I think you need to measure the voltage at the 12 V Aux outlet when the high indicated voltage condition is present. For flight safety that may require making up a 12 V plug test lead.

Poor ground connections can skew GEA 24 readings but the challenge may be to find where this one is.

Alternator noise suppression is typically by a large value capacitor between the alternator output and ground. The alternator ground path is typically from the frame of the alternator, though the alternator mounting bracket, to the motor crankcase. Often there is a ground strap directly from one of the alternator mounting bolt directly to the crankcase. The suppression capacitor should have no influence on the DC grounding of the alternator.