scsmith
Well Known Member
I guess the best way to tell this, and ask questions about it, is to start from the beginning.
I replaced the Odyssey PC-680 battery about two weeks ago. Was fine for several flights.
I had an avionics shop do a 91.413 transponder check, which involved having the avionics powered up by the battery for, oh, probably 10 minutes.
Just after that, I started the engine with the alternator field switch off, as I always do, it cranked fine and started right up. I did not happen to notice the buss voltage. Then I turned on the field switch and the avionics master, as I always do, and a bunch of strange things happened all at once.
The Dynon EMS-120 display blinked out for a second, then came back showing, just for an instant, a buss voltage of 8.5V, then 15.1V, where it stayed. But the display showed -3 amps, meaning that the battery was discharging to power the avionics. Three amps is about the right load that I normally see, but it should be +3A.
I turned the field switch off, and the buss voltage dropped to 10.9V, and the current remained -3A. I turned the field switch back on, and the voltage again went up to 15.1V, but the current remained -3A.
How can it be that the alternator is putting 15V into the buss, but no current, so that the battery is still discharging? And why was the battery suddenly down to 10.9V?
I have a feeling that two separate failures occurred, perhaps one causing the other.
It seems that the Plane Power voltage regulator has failed and the alternator output is being held at 15.1V by the crowbar? It seems possible that this could be from a high-resistance connection at the field wire plug (that has happened before, although it caused a moderately high output, 14.8V, not 15.1V) or else the regulator just failed.
It also seems like the new PC-680 battery now has a shorted cell. I put it on a charger, and it charges at 13.2V and as soon as the charger is disconnected it drops again to 10.9V.
Did the high voltage cause a failure in the battery? Did a shorted cell in the battery cause the failure of the voltage regulator?
But why and how could the alternator be putting out 15V into the buss and yet not supply any current?
As a final detail because it is necessary to make sense of all this, the ammeter shunt is located between the battery contactor and the power buss, and the alternator output feeds the power buss. So the ammeter indicates current in and out of the battery. + current means battery is charging. - current means battery is discharging.
Looking forward to explanations. Thanks.
I replaced the Odyssey PC-680 battery about two weeks ago. Was fine for several flights.
I had an avionics shop do a 91.413 transponder check, which involved having the avionics powered up by the battery for, oh, probably 10 minutes.
Just after that, I started the engine with the alternator field switch off, as I always do, it cranked fine and started right up. I did not happen to notice the buss voltage. Then I turned on the field switch and the avionics master, as I always do, and a bunch of strange things happened all at once.
The Dynon EMS-120 display blinked out for a second, then came back showing, just for an instant, a buss voltage of 8.5V, then 15.1V, where it stayed. But the display showed -3 amps, meaning that the battery was discharging to power the avionics. Three amps is about the right load that I normally see, but it should be +3A.
I turned the field switch off, and the buss voltage dropped to 10.9V, and the current remained -3A. I turned the field switch back on, and the voltage again went up to 15.1V, but the current remained -3A.
How can it be that the alternator is putting 15V into the buss, but no current, so that the battery is still discharging? And why was the battery suddenly down to 10.9V?
I have a feeling that two separate failures occurred, perhaps one causing the other.
It seems that the Plane Power voltage regulator has failed and the alternator output is being held at 15.1V by the crowbar? It seems possible that this could be from a high-resistance connection at the field wire plug (that has happened before, although it caused a moderately high output, 14.8V, not 15.1V) or else the regulator just failed.
It also seems like the new PC-680 battery now has a shorted cell. I put it on a charger, and it charges at 13.2V and as soon as the charger is disconnected it drops again to 10.9V.
Did the high voltage cause a failure in the battery? Did a shorted cell in the battery cause the failure of the voltage regulator?
But why and how could the alternator be putting out 15V into the buss and yet not supply any current?
As a final detail because it is necessary to make sense of all this, the ammeter shunt is located between the battery contactor and the power buss, and the alternator output feeds the power buss. So the ammeter indicates current in and out of the battery. + current means battery is charging. - current means battery is discharging.
Looking forward to explanations. Thanks.