Thanks MTV. I'm sure you remember a while back when you and several others convinced me that I should go with glass. It makes sense even though it isn't want is planed on putting in my "forever" plane. Sometimes functionality is more important than appearance.

Whee, a redundant battery can be completely isolated for everything but charging, and switched on only when needed. Even with only one alternator.

CamTom12 wrote:Whee, a redundant battery can be completely isolated for everything but charging.

So it's not really completely isolated, right. [emoji3] The charging portion is what I'm most concerned about.

For Experimental aircraft builders/maintainers, you may want to become familiar with this publication which is downloadable here, if you don't already have a copy:

http://www.aeroelectric.com/Book/AEC_R12A.pdf

There are many good examples of aircraft wiring options depending on the degree of redundancy sought. You can jump right in by scrolling to the end and reviewing Appendix Z Power Distribution Diagrams for most typical configurations.

In my relatively low amount of flight hours, only about 2,000, half behind steam gauges and half behind glass, I've found glass to be much more reliable.

Looking back on in-flight equipment failures, I'd rank them in order of frequency as:

1. Vacuum pumps,
2. Electric driven gyros, and
3. Alternators/generators.

In 1,000 hours using an EFIS system, I've had no loss of instrumentation, but did have to replace an encoder knob once. The GRT EFIS was just sent back for a processor and synthetic vision upgrade. They emailed me yesterday to say the memory chips had failed, but there was no indication of that in flight so I wasn't aware of that until they told me. However, the full logbook didn't get downloaded before shipping so I've lost that info from March on due to the memory issue.

This summer headed to Yellowpine for the harmonica festival, the brushes wore out in the alternator. The EIS alarm signaled the voltage dropping right after takeoff; I decided to keep flying. Switching to the Endurance Buss (detailed in the above Aeroelectric Connection Z-11 diagram) allowed me to continue the 2-hour flight to Johnson Creek. The E-Buss reduced current draw so the battery could power the EFIS and EIS the entire time and the radio, transponder, and lights on-demand for the duration of the flight. The current draw of the EFIS and EIS is only about 1.5 amps combined so the 17 amp-hour PC680 Odyssey battery had plenty of charge for the flight and a even a restart once on the ground.

Before returning home, I charged the battery from an external source, started the engine, and flew home using the E-Buss again without issue.

I mention this, because I've had several alternator/generator failures with steam gauges and with much higher pucker factors. Two of those were at night; I didn't notice the voltage drop in time so couldn't activate PCL at the destinations. Winnemucca Nevada is a lonely place to be on a very black night without a radio and not enough fuel to reach Reno. Some kind soul on the ground must have heard me circling overhead and eventually activated the lights, I'm forever grateful for that act of compassion. The freeway was the alternate and I wasn't too sure about descending between the street lights to accomplish that.

The second time was another lonely place, a grass strip in Whitehall Montana. Fortunately, I could make out the grass just well enough to land, while praying the deer weren't feeding on the runway.

Neither night failures are experiences I want to repeat. The EFIS/EIS combination plus the ability to minimize current draw to just the essentials and run on the battery for extended periods is a great advantage when the charging system fails. I only fly in VMC and at night on occasion so I'm not as concerned with redundancy as I would be in IMC. YMMV, of course.

Blackrock

whee wrote:

CamTom12 wrote:Whee, a redundant battery can be completely isolated for everything but charging.

So it's not really completely isolated, right. [emoji3] The charging portion is what I'm most concerned about.

That's fair! [emoji3]

But if you have an alternator failure the main and aux batteries' purpose is to get you on the ground safely. They'll last a while if unnecessary things are shut down (like Mike's story shows). The same as you'd do with steam gauges and an alternator failure.

whee wrote:

CamTom12 wrote:Whee, a redundant battery can be completely isolated for everything but charging.

So it's not really completely isolated, right. [emoji3] The charging portion is what I'm most concerned about.

Whee look into a split battery isolator, have used these on quite a few vehicles. Planning on using the same thing in my Glastar, for the exact same thing.

Cole Hersee 48120 Battery Isolator

There are many different ones on the market, have one on my 1956 Caddy motor home, was on there before I got it and still works fine.
Have another one on my plow truck, and my service truck, you can keep the battery's up on the compressor and the welder with out having to start them.
Essentially a couple of diodes to keep the juice from coming back. Run your + wire to the center and to each battery buss from the other 2 posts.

Whee,

you actually need a battery isolator / automatic charging relay, otherwise you slowly destroy/ shorten the lifespan of your batteries as they are trying to equalize the charge back and forth in a dual battery setup without isolation.

As for safety, the new EarthX aviation batteries have an internal circuit which will detect a battery fault. You can connect a LED to this circuit and have it in the panel or connect it to your EFIS.
Also, your EFIS will detect an alternator failure and you can setup most EFIS to give you a warning when this happens. Even if your aircraft would be equipped with a modern engine with electronic fuel injection and ignition the Lithium lightweight, high AH batteries allow you to have a running engine and EFIS for at least 30 minutes or more depending on AH draw of your electronic consumers. If you run a standard old tech aircraft engine with carb and magnetos you can continue for hours if you desire so, although a system like this would be overkill. A smaller backup battery would be sufficient in this case (powering EFIS) as far as I am concerned.

In normal operations both batteries (dual setup) are isolated and in case of an alternator failure you are able to combine both batteries and potentially can double the AH available to power the essential electrical consumers.

Bagarre wrote:For the serious DYIer, here's something I've been building.

https://github.com/Bagarre/Pi2D2

Interesting. I'll have to take a peek at your code when I get a chance.