Mike S said:Get a copy of The Aeroelectric Connection.
It has a few different E-buss designs depending on how many alternators and batteries you are using.
This is what I'm using, mild variation on Nuckolls.
1. If the main bus feed is moved to the downstream side of the ANL-60 fuse, then if the alternator shorts out and blows that fuse, the main bus will lose all power.
Bob Nuckolls does not fuse the main bus feeder on his electrical drawings.
#4. There is a 25 amp fuse protecting the E-Bus circuit.
A few comments. If it seems critical, I beg your pardon in advance. You've already installed yours, but others are looking.
Numbered diagram below.
1. Move the main bus feed to the alternator end of the 60 amp ANL. The ANL is there to protect against a short fed by battery discharge, the huge amp source, not alternator output. Yes, the pilot can open the main contactor manually in the vent of a short under the panel, but that takes time, the cabin is already filling with smoke, and the melting stuff damages other stuff. Better to immediately pop a big fuse. If you really want an ANL dedicated to the alternator line, fine, just install another ANL on the bus feed.
2. A pair of Schottkys? Diode drop is additive, so what voltage shows on the Mini, with the alternator online, and off?
3. Lot of stuff connected here, if this is really an endurance bus. If something is really needed, doesn't it belong on an essential bus? If we put all the stuff not really needed on the main bus, we can eliminate the endurance bus and one feed diode, which means the essential battery gets a higher state of charge. One can always fire up the main bus later in the flight, if desired.
4. Simple "short or open" what-if analysis goes a long way. For example, short either of these two wires to ground, and what happens? The diode burns open, and the panel goes dark. So you flip the E-Bus Alternate Feed switch...which feeds the short, and there is no fuse on that feed.
5. Odd duck here. The P-mags don't need battery support in flight, so why connect them to the last chance bus? All connections carry some risk. They belong on the main bus, for starting and ground idle.
6. As you noted, the best everyday use for an aux battery is to prevent EFIS brownout during start. Less recognized is that it would also prevent main EFIS reboot if main power is interrupted in flight, like when opening the main before closing the aux. It would not be flight critical, just disconcerting (here the GRT Mini would still be live), but it can be eliminated.
BTW, best if this feed wire is physically separated from the rest of the harness.
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1. If the main bus feed is moved to the downstream side of the ANL-60 fuse, then if the alternator shorts out and blows that fuse, the main bus will lose all power. Bob Nuckolls does not fuse the main bus feeder on his electrical drawings.
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#2. I agree with Dan. Two diodes should not be in series.
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#3. Just call it the "E" bus.
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#4. There is a 25 amp fuse protecting the E-Bus circuit.
#6. The aux battery could be used for brownout protection of the E-Bus.
#7. There is one too many buses. Simpler is better.
2. Only time Aux Batt bus is getting juice through both diodes in series is when the Main is live and the E Bus is not. There is no flight regime/failure mode where that is planned.....they all get thrown on at startup and off at shut down unless something goes sideways.
Dan asked why Bob Nuckolls does not protect the main bus feeder with a fuse.
His reasoning can be found at the end of this thread:
https://vansairforce.net/community/showthread.php?p=335866
1. ANL is to protect the battery in the event of an alternator short.
end quote
If the alternator shorts, all the current available in the battery will flow through the B-lead to the short. The ANL is to protect that wire not the battery or, for that matter the alternator which has just failed anyway.
If the alternator runs away and produces too high a voltage, the ANL won't do a thing to stop it. That's what the crowbar is for. It shorts the alternator field to ground taking the alternator offline. Without the crowbar the avionics and, sooner or later, the battery would also be damaged.
Ed Holyoke
1. ANL is to protect the battery in the event of an alternator short.
<snip>
The ANL is to protect that wire not the battery or, for that matter the alternator which has just failed anyway.
</snip>