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  • Re: Backup battery switch?

    by » 4 years ago


    I really liked this idea when I first thought about it and rushed to wire it in. After mulling this over a day or two, I'll likely replace the solenoid with a switch at the panel. As an engineer, I'm highly risk adverse and just broke one of my own rules. I'm going to take Rob's advice and stick with the KISS principle on this one.

  • Re: Backup battery switch?

    by » 2 years ago


    Confused!
    How do you restart an engine in the air becous the ALT A & B is dead?
    if..
    - Caution: Do not turn ON the Back-up switch during engine start as this will defeat some of the ECU self-checks.
    -

    If I like to restart the engine do I need to switch on "Start Power" or can I only switch on "Backup Switch" and restart the engine
    or
    Do I switch on "Start Power", start the engine and then go over to "Backup". Feels a little bit tricky.
    Hard to find in Rotax documentations about backup and operating procedures.

  • Re: Backup battery switch?

    by » 2 years ago


    In an emergency: just flip the "back-up" switch ON and hit the starter.

  • Re: Backup battery switch?

    by » 2 years ago


    I am wiring up a 912iS engine. The latest drawing from Rotax (jan 01 2019) 24_00-00 Page 33 shows both the start power switch and the stand by power switch with double poles connecting the battery to the fuse box AND, on the second pole connecting to earth. But the drawing does not show which EARTH. The battery has to connected to airframe earth. On the earlier drawing Page 31 it shows these switches connected to EMS ground. Thus there is not a complete circuit to the battery, unless somehow the fuse box connects. The drawing also shows the starter motor connected to airframe ground. But the engine and mount are insulated from the airframe. Thus to wire the engine as per drawing on page 31would result in linking airframe and ems ground. OR AM I TOTALLY MISREADING THE DRAWINGS!!

  • Re: Backup battery switch?

    by » 2 years ago


    On Page 33, The Triangle Ground that only appears inside the Regulator Board A is the EMS Ground.
    The 3 prong pitchfork Ground that appears everywhere else is the Airframe/Battery ground.

    As noted, The Engine Block is NOT grounded through the Engine Mount.
    The Engine Block will need to be connected to the battery ground with a Cable the same (Large) size as the 12v starter cable to complete the start circuit.

    As noted, One side the DPDT Start and Backup switches connect the EMS Ground to the Battery Ground during Start or when Backup Power is enabled.
    This places the EMS Power and Ground in parallel with the Battery Power and ground.
    Without the grounds connected together, the battery will not have a return path.
    The grounds (and Power) are isolated during normal engine operation and only connected together when the battery is being used as the primary power source.

    The EMS Ground only exists within the EMS Module, within the Fuse Box, within the Engine Wiring Harness, and on the A-Regulator Ground Plate which is the only place where it is externally accessible. Nowhere else!
    The Engine block is NOT part of the EMS ground.
    The engine block is electrically floating until you intentionally connect it to the Battery to make it a part of the Airframe ground.

    The drawings are correct and you are reading them correctly.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


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