Something to consider rather than a two battery system is a two alternator system. Of course that depends on the engine and drive pads available on the engine. The difference is that with a two battery system, if the alternator fails, the second battery gives you time to get on the ground, but is definitely going to ruin your day if you are traveling any distance. With a backup alternator, if the primary alternator fails, you switch to the backup alternator and shed loads if necessary to match the output of secondary alternator, and continue your trip.
I helped a fellow builder design a redundant alternator system for his aircraft a few years ago when he switched to a solid state ignition system to replace his magnetos. This spring while enroute from New Mexico to Ohio, his primary alternator failed. He simply toggled over to the back up alternator and finished the trip to Ohio and the return trip back to New Mexico before he pulled the cowl to diagnose the primary alternator issue. Regarding the Lithium Iron battery technology, EarthX is making a nice battery designed for aviation use with redundant battery management systems. It has an on battery LED as well as a wire from the battery that can be connected to your EFIS or a panel LED that will flash if the primary battery management module has a problem so you can replace the battery before the backup battery management system fails. The EarthX battery management system will disconnect the battery from the system if the voltage drops below 9 volts or is driven above 16 volts. The battery can be re-enabled by applying a 12V source to the battery. The EarthX batteries aren't cheap, but they are reliable and pack a lot of power into a very light weight package. I switched to an EarthX to provide twice the cold cranking amps as my previous battery in a much more compact package that weighs 4#, instead of the 14# battery I removed. -Jeff Scott Los Alamos, NM ---------------------------- Cc: svd <osprey...@yahoo.com> Subject: KR> Two Battery System My son’s plane has a compufire dual ignition system (though I’m still thinking of a distributor less system). I’m planning to have two small-ish LiFePO4 batteries. Can someone point us to a few good circuit diagrams for aircraft electrical system involving backup power (two batteries)? Should I just have a battery selector like on a boat (off, #1, #2, All)? Cheers, Owen _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
