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Two batteries on the firewall? Backup Battery

in 912iS Technical Questions 10 years ago
I'm wondering if it makes sense to run two batteries on the firewall as a safety measure. I read previous battery postings that stated that Rotax prefers lead acid but if a lithium battery is used it should have a battery management system.

We all know about the Odyssey batteries....two of them, would be the heaviest. Or perhaps I could have two Earthx lithium batteries, which have the management system.

Another alternative would be the standard Odyssey and a TCW Technologies Backup Battery System....:http://www.tcwtech.com/IBBS.htm

Thoughts?

  • Re: Two batteries on the firewall? Backup Battery

    by » 10 years ago

    I think two batteries is excessive and complicated for the pilot; you already have 3 redundancies: both alternators and the battery. if any one fails the other will take over.
    I do like the TCW for backing up the instruments.
      
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  • Re: Two batteries on the firewall? Backup Battery

    by » 10 years ago

    Rob, thanks for responding. With the 912is what happens if the battery fails? Does the engine continue to run? What about ECU's and fuel pump? I am not familiar with the failure modes of the engine yet. Thanks....
      
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  • Re: Two batteries on the firewall? Backup Battery

    by » 10 years ago

    Yes, the engine keeps running if the battery dies or the master is shut off. The ECU and fuel pumps are powered by one of the generators.
    if you lose Gen A then Gen B takes over. Some battery charging is available but the priority is to keep the engine running so you may have to shut down some equipment. Thats why "pullable" c/b's (circuit breakers) are so nice.
    If you lose Gen B then Gen A takes over. The battery will not be charging (but there is a workaround: turn on back-up switch, pull OFF all c/b's, then turn ON the most important c/b's while watching the ammeter for a discharge, re-pull the least essential c/b's until you get a positive charge.
    If you lose both gens; turn on the backup switch and the battery will keep the engine running until it goes below min volts (have to look that number up)
      
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  • Re: Two batteries on the firewall? Backup Battery

    by » 10 years ago

    My Kitfox SS7 came with a 12 cell Aerovoltz on the fire wall. With all the loads required before
    starting the engine I changed to the 16 cell Aerovoltz on the firewall. I mounted the 12 cell
    behind the pilots seat using a switchable circuit breaker and a double pole double throw "no center off" backup power switch.
    I can charge the 12 volt and then isolate it as a dedicated ECU backup power, or I can use it in parallel with the main battery, or as a substitute for the main battery. The Advanced 5600 EFIS has the capability of monitoring the charge condition of both batteries.
    The emergency power section of the aircraft checklist sets the procedures for operation depending
    on the condition of the A and B alt.
    In daily operation the 12 cell rarely needs to be charged as it will stay at +/- 13.2 volts for
    several weeks.
      
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  • Re: Two batteries on the firewall? Backup Battery

    by » 9 years ago

    Hi Guys, my name is Phill. Question Rob, how do we know if both Gens have failed? I assume a drop in voltage represented on the Dynon screen followed by by red color warning when dropped below the set value? Excuse my ignorance but this is the first electronic controlled engine i have flown with and i go cross eyed reading the manual over and over. Thanks
      
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