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Thread: 912iS HIC A. HIC B question

  1. #1

    Default 912iS HIC A. HIC B question

    Just about finished with the wiring behind my panel but have a question about the HIC connectors.
    On the Rotax info that I have it shows HIC A, pin 4 as a “display” CAN ground and HIC B, pin 6 as a “display” CAN ground.

    Do I ground these at my ground buss or to one of the EMS ground wires? Does it matter?

    Hoping one of the Team Kitfoxers can steer me in the right direction. Thanks in advance.
    Joe Gallagher
    Building SS7


    http://frontierfox.home.blog

  2. #2

    Join Date
    Apr 2012
    Location
    Oak Harbor,Wa
    Posts
    156

    Default Re: 912iS HIC A. HIC B question

    I have a kitfox SSS7 with a 9121S. The can buss output from the CPU is connected as follows: My display (Advanced 5600) has only one can buss input so can A and can B high are connected together on the high input of 5600 and can A and can B low are connected together at the low input of 5600. The can A and can B grounds are connected to a floating display ground on the 5600 chassis. As directed by Rotax the can A and can B maintenance outputs are connected to sub d 9 pin connectors for use with the BUDS program. The 5600 recognizes and separates the A and B signals as does the BUDS program. A separate Rotax diagram shows a connection method for the A and B maintenance signals to be combined for the BUDS program or connected for monitoring one channel a a time.

  3. #3

    Default Re: 912iS HIC A. HIC B question

    Sounds like I have the CAN high and low connected correctly however I’m not sure what you mean by a “floating ground” on the 5600 chassis. I don’t see anyplace to connect a ground on the chassis. Do you have a pic?

    My maintenance CAN’s for the BUDS system are good. Just not sure about the Display ground.
    Joe Gallagher
    Building SS7


    http://frontierfox.home.blog

  4. #4

    Join Date
    Apr 2012
    Location
    Oak Harbor,Wa
    Posts
    156

    Default Re: 912iS HIC A. HIC B question

    Floating ground: the chassis (the case which contains the electronic components of a device) is normally grounded to the airframe by the fasteners which hold it in place. However, in some cases the unit cannot tolerate the evil electronic current running around on/in the metal frame of the aircraft. So in that case the electronics ,or some of them, are mounted in the case so that they are insolated from the case. That unit may have a separate ground lug which is connected to an AVIONICS GROUND BUSS, which is usually mounted behind the instrument panel, and is also insulated from the aircraft frame and has a connection through the firewall to the main aircraft ground which is usually located on the engine mount or the engine its self.

    In the case of the Advances 5600, looking at the back of the unit one sees a sub chassis which is insulated from the rest of the unit and has a ground lug in the middle. That is where my can buss grounds are connected. All of the signal cable shields feeding into or out of the unit are also connected to this floating ground. This point has a wire connected to the Avionics ground buss and thus is connected to the main aircraft ground. , but not by using the aircraft frame.

    You mentioned connecting to the A lane grounds. I would not do that, as that ground point is for the ignition system of the engine and you would be supplying a continuous ground, which would over- ride the momentary ground supplied as a function of the start switch.

  5. #5

    Join Date
    Apr 2012
    Location
    Oak Harbor,Wa
    Posts
    156

    Default Re: 912iS HIC A. HIC B question

    More on floating grounds: The A regulator ground terminals, the starter solenoid, and the ignition coils are all part of a floating groung system. The start switch is required to connect the battery voltage to the engine start circuits until the alternators come to life and when released returns the ignition system, including at least the CPU part of the ignition system, to a floating condition. ( Do not know the internal working of the CPU as that information is proprietary to Rotax). That floating ground is why the starter solenoid has the white insolating disk to keep it away from aircraft ground at the fire wall mounting.

  6. #6

    Default Re: 912iS HIC A. HIC B question

    Thank you for the guidance Neville.
    I took a close look at the chassis and there is no stud of any kind to act as a floating ground. I think that possibly there is a difference between your chassis and mine. I had Advanced Flight Systems make up most of my harnesses and I bought my components from then including an ACM. This might be where the difference is. All of the component harnesses connect to the ACM for power and ground so I feel confident that grounding HIC A and B to the ground buss will be the best.

    My regulators are of course isolated from the chassis.

    I’m going to check everything over of course before I power the system up. Gotta keep the smoke inside.
    Joe Gallagher
    Building SS7


    http://frontierfox.home.blog

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