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avionics and E-bus

iowaflyer

Active Member
I know the pros and cons of an avionics bus/switch so not looking for advice about that. And, I've done a search and can't seem to find an answer.

I'd like to put my com radio on an Endurance bus but still have an avionics switch controlling it and the remainder of the avionics not on a the E-bus. I can't wrap my head around a possible way to do this. Thoughts? Maybe I just put it on the E-bus with EFIS #1 have it on during engine start
 
I think you are going to have to make a decision. I don't think you can do what you want to do. The Avionics and the Endurance busses have separate power sources normally. The Avionics Bus is normally powered through a switch/relay from the Main Bus.

I don't think this does what you really want, but it sort of sounds like what you are asking for. Use a double pole switch for your avionics switch. One side is used for your COM1 and the other for your relay for the other avionics devices. The COM1 side is powered from the Endurance Bus to COM1. The problem with this is you will lose your COM1 if you turn off the avionics switch. This might be the normal failure condition on switching to the Endurance Bus.

In my system I moved my COM1 to the Endurance Bus. I can do an engine start without Avionics or the Endurance Bus turned on. Then I can switch them both on. I'm not sure if that was what you were thinking about or not. Yes I know that some folks say the avionics is robust enough these days to not have to do this.

I don't want to have to mess around with doing a bunch of switch operations. I can turn things off if needed in an emergency by turning off my avionics switch or master even if need be. No switch over to Endurance Bus required since it is already switched on I just need to turn off other devices.
 
So if I understand correctly, you want to have multiple boxes controlled by a single avionics master, but fed by different busses?

If that's the case, seems like a double pole switch would do that if you ran from the E-buss through one side of the switch to power comm 1 and the other side powered from the main buss to your other stuff.
 
Thank you guys very much. Yes, that is exactly what I want to do. E-bus feeding com and avionics bus feeding everything else. I didn't even think about running power to the com through the avionics switch AFTER it leaves the E-bus.
 
One follow up thought though- I know this was my suggestion, but now that I think about it, I can see a downside.

Even though you have two buses that switch now becomes the single point of failure for all your radios. Seems like there ought to be a way to do it though with some diodes and whatnot though. would just need to ponder it a bit more...
 
I used to have the eBus fed through a diode from the main bus and alternatively through a switch powered from the battery bus. (Aeroelectrics diagrams).

In a couple of weeks, I will redo the electrical system on GERZ. I plan on the aux battery to feed the radio, EFIS ans engine instruments directly. Both main bus and aux bat would feed those through Schottky diodes. The Aix battery will be a LiFePo4 maintained by a Dc-DC adjustable voltage and current converter.
 
I think you should think about the case where you would want to use the Endurance Bus. I think in that case you would be turning off the avionics switch. With your method you will be turning off COM1. You might as well just put it on the Main Bus.

I thought of an extension of using a separate pole for COM1 Idea. Wire the main bus up to on position. For the off position connect the Endurance Bus power and COM1 power to the common. Then when the Avionics switch is off the COM1 radio will get when the Endurance Bus is switched on. When it is on power will come from the Main Bus.
 
Schottky diodes are your friend. I used them to provide many power paths to my essential items without me having to do a thing. The Avionics Switch is to isolate things during a start. If I get down to my E-buss, the avionics switch will still stay on, I will use individual power switches to shed loads if needed. As it turns out, the E-batt can power everything for 30 minutes plus (limited comm transmissions), which ought to be enough to get my plane on deck in IFR conditions. I confirm that performance every year before my condition inspection, and then replace the E-batt with a new one as part of my inspection.

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