Electrical issue - thoughts?

[Michael Fadden]

My rarely flown Pegasus had its last annual 1 year ago and sat unused for nearly two years until this June. During the annual in 2023 I noticed the Trig transponder wasn't working or, at least, not displaying.  I don't recall if i turned  on the vario or the Becker AR 3201 radio at that time. I intended to pull the transponder and send it out for service but never go around to it.   The 2 hour drive to the airport and my almost total lack of flying the glider made me lazy.  Fellow club members said "Label it "Inop" and go fly".

Back in June a good soaring day came along and I rigged to do just that. The transponder was still not working properly and I turned on the radio to set a channel in memory. The vario (Borgelt B700) came to life and I shut everything down as it was going to be a while before I launched. An hour later as i was getting ready to go I noticed the radio display was not correct, showing a single vertical LCD in the bottom right of the screen. Picture the bottom right section of an 8. The radio did this once before a few years ago and I (as it turns out, incorrectly) attributed it to a low battery. The issue didn't arise on the next flight and I forgot all about it. This time there was no sound from the radio. Fortunately, I had a handheld that worked fine. After I launched i noticed that, while the vario was functioning correctly, there was no audio. The radio and vario share the same speaker. The flight went just fine with plenty of strong lift, although not having audio was a pain.

I'm going to be taking the glider into the local repair shop to have someone, who is better versed than I in electronics, troubleshoot. Going through the manuals I'll be taking, I saw the the vario manual said to not use 14 volt batteries as, when fully charged, they can output more than that.  I just checked the voltage on my on my 12 volt LiFePO4  battery and it read 16 volts. What?  I've used this battery and charger for a few years. I checked the charger output and the label said 15 volts. The label also said for 14.7(I think) volt batteries. The battery has no bulges or other sign of distress. I don't know how I missed that when I bought the charger but I did. I'm pretty sure it was the or, at least, a recommended charger but can't swear to that. 

So, what is the likelihood that I've fried instruments? Why would that happen after operating normally for 4-5 years? Any other ideas? I guess critters might be behind some of it but I didn't see any of the normal signs of mice etc. A closer inspection is in order. 

The trailer had some water intrusion near the nose of the ship. Maybe dripping water found its way behind the panel? I think it unlikely but who knows? 

BTW, the Becker rep said he's never heard of that display. It flashes when the battery is getting low. 

Thanks in advance. 

[Moshe Braner]

Was it 16V after disconnecting from the charger, and some time passed, and even made some use of the battery?  Strange.  Try another voltmeter to confirm?  Try another battery and see if the instruments come back to life?

LFP batteries are supposed to have a BMS within that prevents overcharging above about 14.6V, regardless of what the charger attempts.  But if that BMS failed, and your charger was designed for 7-cell lead-acid batteries, who knows?

[George Haeh]

I would recommend a careful perusal of the manuals. As I recall 14V or even a few more is unlikely to damage nominally 12V avionics. 

The Trig manual describes how to see the supplied voltage. Rodents may have compromised one or more wires which may have caused a voltage drop. 

A few V below 12 hurts performance more than a few V above.