I was going to have 2 EarthX batteries but changed to a Lead Acid for primary and Earth X as secondary, all FWF. You should look at Mike Bullocks runaway alternator issue to see additional considerations. If you take the battery out of the circuit by shutting off the master you will get a load dump into your panel. A lead acid battery makes a good load to help absorb a runaway alternator. You still need to provide a clamping circuit to hold the voltage down. But both provide a belt and suspenders for a runaway alternator. A lead acid battery will handle the runaway better than a Lithium battery.
Do not depend on a Lithium battery to act as an absorber for this. Over charging is one of the ways you can put your Lithium battery into thermal runaway. It can happen spontaneouslly too but that should be rare, most happen because of excessive charge or discharge.
I plan to monitor the temperature of my Lithium battery using a thermalcouple dedicated to it. Lithium batteries don't like to be charged when they are hot so I want to understand what temperatures it is seeing in the engine compartment. Especially when being charged.
Something else to consider. There are concerns about mixing battery technologies. Hopefully they can coexist if hooked together for short periods or primarily in the prescense of a good alternator voltage, where both can remain fully charged.
In my case if I see a high voltage on the bus, I'll take the Lithium battery out of the circuit first. Also I can switch either out of the circuit if the alternator goes to 0v. That way only one battery at a time is providing source to the panel if a loss of alternator occurs but I have access to both. I should have more battery to power the panel than I have fuel to fly.
Just some things to consider. I'm not a battery expert so take this as things to think about. I have been looking into this and this is where I'm at right now.
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Last edited by rgodsy : 10-19-2017 at 01:30 PM.