Lane voltages higher than battery viltages

Andrew,
It’s easy to get confused between Alternators A and B and Lanes A and B.  In normal operation the alternators are fully isolated, including the grounding systems. Once the startup sequence is complete, alternator A powers engine functions and alternator B provides power for the airframe systems. A detailed description of the system operation is available in section of 24-00-00 of the 912iS installation manual, page 10 of this section is particularly relevant.  

I suspect that when you are referring to Lane A and B voltage, you are actually looking at Alternator A and B voltages.  On many aircraft two voltage readings are displayed, one for the ECU power bus, and one for the Airframe power bus.  This is essentially the display of Alternators A and B (which are isolated from each other) but this is not the same as voltages for Lanes A and B.  Your readings of 13.8 and 14 volts make sense in this context and are completely normal.  This would assume the battery voltage of 13.1 you referenced was measured with the engine off. 13.1 volts is a reasonable resting voltage for a Lithium battery, but would be considered low with the engine/alternator running. 

Back when computer programs had instructions, there was an expression, RTFM, which was something about reading the manual!

geoff klestadt wrote:

operators manual section 7-4

Back when…

Jeff Blakeslee wrote:

Andrew,
It’s easy to get confused between Alternators A and B and Lanes A and B.  In normal operation the alternators are fully isolated, including the grounding systems. Once the startup sequence is complete, alternator A powers engine functions and alternator B provides power for the airframe systems. A detailed description of the system operation is available in section of 24-00-00 of the 912iS installation manual, page 10 of this section is particularly relevant.  

I suspect that when you are referring to Lane A and B voltage, you are actually looking at Alternator A and B voltages.  On many aircraft two voltage readings are displayed, one for the ECU power bus, and one for the Airframe power bus.  This is essentially the display of Alternators A and B (which are isolated from each other) but this is not the same as voltages for Lanes A and B.  Your readings of 13.8 and 14 volts make sense in this context and are completely normal.  This would assume the battery voltage of 13.1 you referenced was measured with the engine off. 13.1 volts is a reasonable resting voltage for a Lithium battery, but would be considered low with the engine/alternator running. 

I really need to read the manual. 

Bill Hertzel wrote:

Andrew Asked,

So does that mean that the alternator powers the lanes and not the battery?
YES!

Does that mean that the alternator always produces maximum voltage even if there is not much of a load?
YES!

Does that mean the battery never discharges under normal operation?
YES!

Does it not even act as a sort of capacitor for fluctuations in load or voltage? 
Only for the Panel Loads, Not the Engine.
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It sounds like you understand it all pretty well.
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To determine what is causing the Intermittent Lane Fault, Connect your BUDS Software and interrogate the Fault Log.

Thank you for your replies. One thing I am *really* curious about though, will the buds give me more info than the Dynon screen? Could the Dynon be misleading? It just said “ignition coil 4”. I really appreciate your time everybody!