Avionics Bus Max Voltage and Protection
Posted: Fri Aug 05, 2022 10:45 pm
For engineers and the technically inclined:
Has anyone tried to characterize how clean the electrical buses are (ie Main Bus or Avionics Bus) on the Lycoming DA40-180? I upgraded my cigarette lighter plug to supply up to 7.5A to drive an Inogen One G5 oxygen concentrator. My shop installed a new 10A plug with thicker wiring through a 7.5A breaker connected to the Avionics Bus. I was planning to use Inogen Aviator's DC/DC supply to convert 28VDC ship power to 12VDC to run the G5 with the manufacturer's 12VDC car plug. But that supply unavoidably creates switching noise, thus EMI that can interfere with radios/navigation.
From reading the specs online, I assumed Inogen's AC/DC standard brick also supplied 12V to the device. I was surprised when I received the Inogen G5 device today and found that the standard AC/DC supplies 24VDC @ 5A to the G5. That says to me that the G5 will run anywhere from 12V to 24V, probably just drawing twice the current at 12V.
While I wouldn't want to run a 24V device directly from ship's 28V power, I am thinking it might be good to construct a DC cable that plugs into the lighter plug, then cascades 6-8 10A diodes in series to bring the 28V (my G1000 usually indicates about 28.2VDC) down to 23-24V for the G5. That way I avoid the switching noise generated by Inogen Aviator's DC/DC power converter. The diodes would create some heat, but that should be manageable.
What I'm wondering is the following:
1. Which bus is the G1000 monitoring?
2. How well regulated is the Aviation Bus?
2a. What is the maximum voltage seen on the Aviation Bus?
2b. How much ripple is on the Main or Aviation Bus?
3. Is there already good over-voltage protection, ie to minimize load dump**, on the Aviation Bus?
Automotive power supplies usually need to accommodate load dump, which is a high energy transient (in simplistic terms - think big voltage spike). I'm thinking power on the Avionics Bus must already be protected from load dump to avoid frying a G1000 or electronic subsystems downstream.
**Description from one of my prior companies: In automotive systems, a load-dump transient occurs when an alternator is delivering current to a battery and the battery is abruptly removed. This can happen when a discharged battery loses connectivity while the alternator is generating charging current and other loads are connected to the alternator circuit.
Thanks for any thoughts on my questions and this approach.
Has anyone tried to characterize how clean the electrical buses are (ie Main Bus or Avionics Bus) on the Lycoming DA40-180? I upgraded my cigarette lighter plug to supply up to 7.5A to drive an Inogen One G5 oxygen concentrator. My shop installed a new 10A plug with thicker wiring through a 7.5A breaker connected to the Avionics Bus. I was planning to use Inogen Aviator's DC/DC supply to convert 28VDC ship power to 12VDC to run the G5 with the manufacturer's 12VDC car plug. But that supply unavoidably creates switching noise, thus EMI that can interfere with radios/navigation.
From reading the specs online, I assumed Inogen's AC/DC standard brick also supplied 12V to the device. I was surprised when I received the Inogen G5 device today and found that the standard AC/DC supplies 24VDC @ 5A to the G5. That says to me that the G5 will run anywhere from 12V to 24V, probably just drawing twice the current at 12V.
While I wouldn't want to run a 24V device directly from ship's 28V power, I am thinking it might be good to construct a DC cable that plugs into the lighter plug, then cascades 6-8 10A diodes in series to bring the 28V (my G1000 usually indicates about 28.2VDC) down to 23-24V for the G5. That way I avoid the switching noise generated by Inogen Aviator's DC/DC power converter. The diodes would create some heat, but that should be manageable.
What I'm wondering is the following:
1. Which bus is the G1000 monitoring?
2. How well regulated is the Aviation Bus?
2a. What is the maximum voltage seen on the Aviation Bus?
2b. How much ripple is on the Main or Aviation Bus?
3. Is there already good over-voltage protection, ie to minimize load dump**, on the Aviation Bus?
Automotive power supplies usually need to accommodate load dump, which is a high energy transient (in simplistic terms - think big voltage spike). I'm thinking power on the Avionics Bus must already be protected from load dump to avoid frying a G1000 or electronic subsystems downstream.
**Description from one of my prior companies: In automotive systems, a load-dump transient occurs when an alternator is delivering current to a battery and the battery is abruptly removed. This can happen when a discharged battery loses connectivity while the alternator is generating charging current and other loads are connected to the alternator circuit.
Thanks for any thoughts on my questions and this approach.