Question TCW IBBS (3AH) volts?

[Neal]

Everything has been working great, had an enjoyable golden hour flight tonight, OAT 60F, perfect conditions. I turned on IBBS and saw 12.7V wondering what the state of my IBBS battery is. That seems a bit low if it is in fact a LiFePO4 battery. Maybe it's because I haven't flown enough to get it charged? So I'm curious from others, when you turn on IBBS, realizing it's under load, what voltage are you seeing?

During flight I saw a max of 13.3 which seems odd as my other two LiFePO4 (EarthX) batteries show 14.1V at full charge. Maybe it's not charged yet? Maybe the battery has a bad cell? What are you seeing for a fully charged TCW IBBS battery?

 

[Cactus Charlie]

My FX-3 AFM supplement includes the following text -

"The normal IBBS charging cycle has IBBS volts gradually increasing to about 14.2 V then gradually dropping to about 13.3 V where the charging cycle starts again. IBBS will not be at maximum capacity until IBBS Volts has risen, at least once, to about 14.2 V after engine start."

and this graphic -

In flight the main battery and ignition battery display MAIN bus volts which is not a useful indication of battery condition. IBBS volts is the actual battery pack voltage not MAIN bus volts.

 

[Neal]

In flight the main battery and ignition battery display MAIN bus volts which is not a useful indication of battery condition

Not sure I fully agree. For example my backup ignition (EarthX ETX-104) doesn't just peg at 14.1V when on the main bus. The state of charge is not 100%. The voltage rises for example yesterday from 13.7 to 14.1. Granted, off charge the volts would show more like 13.0-13.3 and not 13.7. But there is still indication of a charge and then it peaks at 100% state of charge.

The IBBS is interesting. So what is your state of charge which is what I wish we would see instead of volts. This is how my RV (motorhome) is wired using a shunt to measure the current flow. Regardless of charging amps I see the actual state of charge of the battery. So with the IBBS I'm curious what the state of charge is and for those using it as a backup ignition battery this is important to know for what you can expect should you need to use it.