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  • Re: Backup battery switch?

    by » 4 years ago


    It is a new plane, and no electrical diagram available. ...

    We do have a shunt installed for the G3Xs. This is located in the cockpit, but I'm not aware (yet) how it is connected. I believe it is connected directly to the wire coming from the battery. It used the standard "crimp" connectors you use in a car. When I had to change the two wires (showed negative value when charging!), one "connector" did fall off. To my knowledge, if this connection breaks the engine will keep running, but if the ALT-A+B will fail, then I cannot switch to backup battery. It must run through the shunt too. I really need to solder them to the connector to make sure this will not fail.
    Do you agree? The shunt should be mounted on the wire from the battery, before or after the main switch?

    I think I have to start measuring around the plane and check if the installation is what Rotax recommends. I just need to find the way the charge current flows.


    A new plane should NOT need to be rewired!
    The Basic wiring diagram is part of every "Pilots Operating Handbook" POH that is required to be in every plane on every flight.

    The X3 connector...

    Pin #1 ... Backup Battery Power IN to the Engine. Emergency Backup Power. This switch should have a cover over it to prevent accidental operation except for Emergency use.
    Pin #2 ... Temporary Starting Power IN to the Engine. Used Only during Startup. Almost identical function to Pin #1.
    Pin #3 ... ALT-B Power OUT from the engine. Used to charge the battery and power the Instruments.

    With MASTER and BATTERY Switches ON, Engine OFF, you should see the 12v Battery voltage on X3 Pin #3 of the wiring harness with the connector removed from the Engine/Power X3 plug.
    This is where the Battery connects to the ALT-B.

    And Again, This is not your problem. It is a Manufacturing Fault. And a major one!!!
    Almost having an engine fail due to an electrical problem on the maiden flight is cause to ground the aircraft.
    If the manufacturer is not treating you like like it is a very big deal, It is time to get the (DTA) Danish Transport Authority involved.
    They should have never sold an aircraft that can't complete the first flight.
    If they are just going to ignore the problem, they should never sell another aircraft.

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


  • Re: Backup battery switch?

    by » 4 years ago


    Hi Bill,

    Most of the light aircraft MFG's made wiring errors when the 912is engine came out. Some have fixed those errors and others are painfully slow to change or help the customer. MFG's that thought they knew more than Rotax and bypassed or re-engineered instructions. Unfortunately the customer has had to fight some MFG's for help and somer MFG's have sparse service centers that can help.

    Either way the end user had to pay in problem solving.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: Backup battery switch?

    by » 4 years ago


    Hi Rodger,

    I can understand an amateur-built aircraft getting Snafu'd.
    But a Certificated, Production aircraft that is being built, sold and losing all power on the delivery flight is inexcusable.

    The work needed to re-engineer his problem is way beyond the capabilities of most owners, and in the US, under the LSA Rules, only permitted by the manufacturer.

    I understand the OP (Original Poster) is in Denmark. But Denmark is not some backwoods third world country.
    The DTA should have enough clout to prevent future imports of the aircraft if the manufacturer is unable to deliver a plane that is at least flyable without the owners having to rewire a brand new airframe.

    Most A&P's would have difficulty trying to sort this out.

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


  • Re: Backup battery switch?

    by » 4 years ago


    "But a Certificated, Production aircraft that is being built, sold and losing all power on the delivery flight is inexcusable."

    You got my vote. Now we just have to convince people they really don't know more than Rotax and there really is a reason things were done that way at the Rotax engineer level and Rotax MFG level. :)
    If the last 20 years has shown anything that means it's an uphill battle. :silly:

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: Backup battery switch?

    by » 4 years ago


    Hi all

    Thanks for the interest, and thank you for helping :)

    To be fair. If we did follow the checklists we would not have gotten into the problem on the way home. The checklist is at the top of this thread, and it do specify how the switch should be used (I know it is not correct). But we did not have the checklists except in a printed manual in the luggage, and the pilot (I cannot fly it yet) was sure the switch was not used at hand over training flight. I have been reading the manuals before delivery, and I have never found anything about this switch, so I did not know what it did.
    This combined with the fact, that when everything started to fail (first autopilot, then transponder, then G3Xs) I KNEW that we did charge because I had seen +13A before Garmin died. The second problem was that the shunt wires were swapped. It was actually -13A, but I could not know that.
    Looking back at it, the engine would have kept running. No faults on Lane A and B and ALT-A and B worked.

    That reminds me that the two Lane A and B indicators do light when they are off, so I need to mount the parallel resistors too ;)

    Good thing is, that I'm a electronic engineer, so normally I take things apart to see why they work. This time it makes even more sense B)

    I'm going to the plane tonight, and we will start working on figuring out if everything is okay except the reversed backup battery switch. But it is a really good idea with the lid on the switch. I will see if I can find one. I will also change the two Lane A/B LEDs. They are really not visible in sunlight. And while at it, I will add wires for Lane A/B to the Garmin G3X to show the warnings on the display.

    Have now had the plane for 14 days, and have still not started my flight training (coming from a motorglider) on it because of bad weather :angry:

    I will send an update tomorrow.

    Kind regards, Claus

    PS. When I'm done with the corrected checklists, I will send them to the supplier. The fact that we were told to switch off the engine using the main fuel pump also turned out to be wrong.

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