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Thread: Current shunt

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    Senior Member Andy's Avatar
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    Default Current shunt

    Does anyone have a circuit diagram (wiring schematic) showing the current sensing shunt that is mounted on the avionics tray? It's not shown on any of the drawings I have and I'd like to understand exactly what it is measuring.

    Thanks,
    Andy

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    Default Re: Current shunt

    This might help. This is a Dynon set up, but the principles remain the same.

    shunt.jpg

    shunt-1.jpg
    Dan Arnold
    KEUL

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    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    Does anyone have a circuit diagram (wiring schematic) showing the current sensing shunt that is mounted on the avionics tray? It's not shown on any of the drawings I have and I'd like to understand exactly what it is measuring.
    Never mind. I found it on the G3X schematics. It's between the master solenoid and Main Bus.

    p.s - thanks for the reply Dan
    Last edited by Andy; 01-09-2021 at 08:16 AM.

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    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    Never mind. I found it on the G3X schematics. It's between the master solenoid and Main Bus.
    I have just got around to this issue. As you said the shunt is between the master solenoid and main bus, so it is only measuring the current charging or discharging the battery. While it is useful information it is a waste of a good shunt that can be used for other purposes.

    Most modern glass panel aircraft display the bus voltage (which we have) and the load provided by the alternator (which we don't have). So there are two ways to go here.

    First, we could repurpose the shunt to be in line between the alternator output and the main bus. The engine configurator will allow this change. With this we will get annunciation anytime alternator output falls below a specified level. This is very useful since we have no annunciation for alternator failure in the G3X setup.

    The second option (which is the route I am taking) is to buy a second shut. They are available at Aircraft Spruce here. The GEA24 has room to take a second shunt. It requires running two wires from the shut to plug P243 pins 34 and 35. These pins are available. You can see holes in the image below near the top of the connector next to the two green wires. The two green wires run to the existing shunt in the G3X install.

    So with the second shunt installed you will be able to see the charge state of the battery and the alternator output with appropriate alarms set up in the engine configurator on the EIS page. In my last SS I had a Dynon HDX panel. I set up the alternator shunt output to alarm anytime alternator output fell below the base daytime load of my aircraft which was around 6 amps.

    Bob Anderson, CC11-00435, N94RA

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    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by turbopilot View Post
    I have just got around to this issue. As you said the shunt is between the master solenoid and main bus, so it is only measuring the current charging or discharging the battery. While it is useful information it is a waste of a good shunt that can be used for other purposes.

    I would like to be able to see/display the emergency ignition battery charge/discharge, the main battery charge/discharge, and the alternator load. That can be done with 2 shunt inputs but it would require 3 shunts and a shunt select switch.

    May be simpler to settle on 2 of the 3. Even simpler to leave it alone.

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    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    I would like to be able to see/display the emergency ignition battery charge/discharge, the main battery charge/discharge, and the alternator load. That can be done with 2 shunt inputs but it would require 3 shunts and a shunt select switch.

    May be simpler to settle on 2 of the 3. Even simpler to leave it alone.
    If I could only monitor one electrical parameter in an all electric airplane it would be alternator output. We have bus voltage displayed for all three batteries. Charge and discharge state of the batteries can be inferred by the voltage. For $39.50 we can have alternator output on the G3X. Not bad compared to spending $300 for CO levels.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member Andy's Avatar
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    Default Re: Current shunt

    I found out that we are not limited to the two shunt inputs. It's possible to customize GP inputs and I set up one for a hall effect current sensor to monitor pitot heat current. Still in the experimental stage and the sensor is not wired yet but looks like it should work.


    Pitot heater current varies with probe temperature so the gage will not only show that the heater is active it should also provide an indirect indication of probe temperature.
    Attached Images Attached Images

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    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Decided to install a second shunt to display alternator output. Set up CAS alerting to annunciate anytime alternator output falls below 5 amps. With current G3X installation in the Carbon Cub there is no annunciation if the alternator goes off line, unless you set a CAS alert for the battery going to discharge. First alert would be when battery voltage falls below alert level.

    Lots of room to mount second shunt right next to the battery shunt on the avionics shelf. Requires two wires from shunt to pins 34 & 35 on plug P-243 of the GEA24. Garmin shunt available from Aircraft Spruce here.





    Last edited by turbopilot; 03-11-2021 at 04:35 PM.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by turbopilot View Post
    Decided to install a second shunt to display alternator output.
    That looks like a useful mod. Where/how did you break into the alternator output?

  10. #10
    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    That looks like a useful mod. Where/how did you break into the alternator output?
    Input of alternator to the 50 amp alternator CB.
    Last edited by turbopilot; 03-11-2021 at 06:00 PM.
    Bob Anderson, CC11-00435, N94RA

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