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Bart

Well Known Member
I flew a G1000 equipped aircraft yesterday and think I realized why many builders have installed battery backup system but want to be sure. Apparently you cannot start with the PFD (Screen) energized without power from a source other than the starting battery. I assume now that the backup system is not necessarily a safety feature as I first thought but a real necessity to see what the engine is doing before the alternators come on line. I hate to sound like a complete moron but never thought through the whole ?glass cockpit? option to this detail and I?m just about ready to start seriously thinking about the avionics. Any thoughts on this would be helpful.
 
I have a back-up battery system but becomes a dual battery system at start-up. Between my EFIS/One, fuel pumps, EFI and all the extra electronics I need two batteries or there just won't be enough juice to get the thing started.
 
I wired my BMA Efis keep-alive to the backup battery, but the battery is there primarily to energize one of my Lightspeeds should the main system fail. My ADI also has a backup battery specifically designed for it. I'd say it was a safety issue. But if you don't need the backup for ignition, there are probably other ways to design it. One of the weaknesses of my setup is that if I lose the EFIS I have no backup engine instruments. I have been thinking of putting in a switch so I can run the EFIS wholly off the backup battery if necessary, but a better idea would be a backup monitor or gauges. Still, in the event of EFIS or main buss loss, my emergency procedure would be to land as quickly as practical and the odds are the engine would be alright during that time. But I'd feel better being able to see the numbers.

Anyway, if you're just keeping the EFIS alive, the backup doesn't have to be particularly big. But a more robust system will be more complicated and require more of the battery.
 
I've written about my Aux battery before, but basically, I didn't have it in the original design, and when I powered up the EFIS before star (on the main battery), then hit the starter, everything rebooted because the voltage got dragged down. Fortunately, the GRT EFIS has multiple power inputs, dioded inside the units, so I simply added a 4.5aH battery which feeds the third power channel, and charge it off the main battery bus through a resistor (to limit current) and diode (to prevent back-flow). As a bonus, it will power the EFIS for 30 minutes should both alternators and the main battery go bad!

Yes, if you want EFIS powered up before engine start, you'll probably need something like this.

Paul
 
I think the Dynon has a backup battery. I know my AFS-3500 has a optional B/U battery (I have the option). My intent is to power up the EFIS/engine monitor on the backup battery for startup. Main power to the AFS is thorugh the avionics bus. I installed a power switch on the panel for the EFIS. I mostly installed the switch to be able to reboot the unit without having to shutdown the avionics bus (only way to rebot the AFS is to kill power to it, then power backup.)
 
It depends

Bart said:
...Apparently you cannot start with the PFD (Screen) energized without power from a source other than the starting battery. I assume now that the backup system is not necessarily a safety feature as I first thought but a real necessity to see what the engine is doing before the alternators come on line...
Click to expand...
It depends on the EFIS. Dynon doesn't seem to care if thier units are powered up on startup or not.

In fact, they recommend the engine monitors, including the FlightDEK D180, are powered up during engine start.

With Dynons, battery backups are available for some units but not all. In my case, the D10 engine monitor does not have a battery backup and has continued to work just fine without any issues, even though I leave it on during startup.

BTW, my starting sequence is as follows:
1. Master on (both sides, including alternator)
2. Both P-mags on ship’s power
3. Strobes on
4. Fuel Pump on
5. Mixture rich, throttle full aft
6. “Clear prop”
7. Engage starter while moving throttle up
8. Check oil pressure on Dynon EMS D10 upon engine start (It powered up with the Master in step 1.)
9. Avionics master on
10. Switch Dynon EFIS D100 to split screen to display engine parameters
11. Continue with pre-flight items
 
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