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  • Re: Backup battery switch?

    by » 4 years ago


    Not that it changes your argument, but note that that diagram is from a old version of the Installation Manual. And the green LED has been added by your OEM, it is not in the Rotax drawing.
    Your aircraft POH is wrong: The Back-up switch must be off for starting and for the entire flight. it is for emergency and ground maintenance use only.
    Is the confusion due to Rotax showing the master switch instead of a master relay/switch combination? Maybe this was done as some OEMs use a large mechanical switch instead of the standard constant duty relay? I don't know but the drawing is correct; the starter motor should be after the master (you should not be able to power the starter with the master off)
    The back-up switch wiring is correct in the drawing you provided, I am not sure why you say pin 2 and 3 are swapped?.
    The back-up switch is poorly named: it is not for a separate battery, it's function is too bypass the fusebox relays and provide battery power to the fuel pumps and ECU (for redundancy) and also provides a means of powering the fuel pumps and ECU for ground maintenance (such as fuel pressure tests and ECU downloading)

  • Re: Backup battery switch?

    by » 4 years ago


    Hi Rob

    The whole discussion is regarding pin 2 and 3 in the X3 connector. On ALL diagrams it is pin 3 that powers the airplane and charge the battery. In this old diagram (feb 2012), pin 2 and 3 are swapped.
    If I can trust what we discussed in this thread, the ALT-B is on pin 3. That is the OUPUT pin that supplies the power to the plane and battery. Otherwise it is ALT-A supplying the airplane. And that is then either on pin 1 or pin 2. For me that is still unclear.

    According to the supplier, the backup battery switch need to be on to "charge" the battery. If that is the case, then it is pin 1 supplying the plane.
    I called Rotax. The guy that took the phone said "we are on vacation" and then hung up!

    This old rev 0 diagram is from feb 2012. Rev 1 is from jul 2012. The certification of the supplier is oct 2012. Why would Rotax certify the supplier based on a obsolete diagram?

  • Re: Backup battery switch?

    by » 4 years ago


    Hi Claus,
    The factory is shut down for holidays, you probably reached the security guard who is tired of answering a 100 calls every hour :lol:

    Must be Monday, I missed the X3 reference.

    Yes, that is an error in that old drawing. The OEM should not be using that drawing for a new aircraft.

  • Re: Backup battery switch?

    by » 4 years ago


    Hi Rob

    But how can Rotax certify a supplier on that diagram?
    And how can a supplier deliver airplanes for 4 years using a wrong diagram?

    and where is the charge coming from? I only thought it was on pin 3, and 1 and 2 are inputs. So how can this wrong diagram supply the plane?

    Kind regards, Claus

  • Re: Backup battery switch?

    by » 4 years ago


    Hi Claus,
    Rotax does not certify any installations, as with any aircraft it is up to the OEM to certify their aircraft and only use the most up to date instructions.

    The power is coming from pin 3 for normal operation.
    Pin 2 is for starting only
    Pin 1 is emergency and ground maintenance only.

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