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Old 12-25-2020, 11:22 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,806

Originally Posted by View Post
Thank you Carl... a new battery is first on my list of to do. Its small-ish AGM. Do folks use Lithiums? Just wondering.

EarthX is the lithium battery most use. I suggest however that for now, you just replace what you have with the equivalent Odyssey battery. After that spend some time reviewing the abundance of VAF posts on people using this battery.

As you gain knowledge on your plane you will be in a better position to decide which way to go.

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Old 12-25-2020, 11:31 AM's Avatar is offline
Join Date: Dec 2020
Location: Buena Vista
Posts: 11

Thanks, much appreciated Carl
2002 Columbia 300 (sold)
2018 Columbia 400 (sold)
1997 SeaRey (sold it buyer sank it!)
1978 Cessna 182 (sold)
1998 Cessna 182 (traded up)
1947 Aeronca Chief (sold)
1955 PA-22 (current)
2008 RV-7A (current)
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Old 12-25-2020, 11:46 AM
Bicyclops Bicyclops is offline
Join Date: Oct 2012
Location: LA, California
Posts: 357
Default Jump started battery and B-lead protection

Jump starting a dead battery will load the alternator pretty hard. The battery is saying "Gimme, gimme, gimme". The alternator will try and match the demand and will make more than rated amps. This will tend to overheat the alternator. Diodes are devices that do not like heat, for sure. Depending on how the B-lead is protected, when you up the load by turning on all the big guns such as pitot heat and lights, it might just blow a breaker. All the old Cessnas route the B-lead to a breaker on the panel that is rated at nominal alternator output. This is bound to pop in such an overload scenario. It happened to me one time when I already had my hands full with a partial engine power failure. A much better setup is an ANL current limiter on the firewall. Those will happily carry much more than rated load almost indefinitely, yet blow when shorted. I know that some RVs have been built with Cessna style B-lead breakers. That might be what happened to the OP. Once the alternator is offline and the battery is already dead... well things get dark right now.

Remember - we need to protect the alternator from the battery, not vice-versa.

Ed Holyoke
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Old 12-25-2020, 12:22 PM
Canadian_JOY Canadian_JOY is offline
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,369

With respect to the OP's question about battery backup for the GRT screens, the answer is an unequivocal YES!

GRT has provided each EFIS with three separate diode-isolated power inputs, power 1, power 2 and power 3. Normally power 1 is normal aircraft 12V from a fuse or circuit breaker on the main bus. Power 2 can be wired to any source of 12V.

In our aircraft I installed a simple 9ah server backup battery; it's small, cheap and readily available, plus it comes with 14" Fast-on terminals so it's easy to wire. This is what I call the Essential Bus Battery.

The Essential Buss Battery (EBB) gets its charge from a circuit breaker on the main bus through a low-loss Schottky diode. The EBB then powers the Essential Bus through a simple on-off switch (appropriately rated for the application). A circuit breaker for each GRT EFIS is located on the Essential Bus and power from each of these CB's is fed to Power 2 input on each EFIS and the primary power input on the EIS.

When wired in this manner their is very little pilot action required to make things work. Hop in the airplane, flip on the Essential Bus switch... the EFIS boxes and the EIS come alive. Go through your normal start routine - as soon as the Master switch is turned on the GRT gear is getting its power from the main bus via Power 1 input. Hit the start button and the main bus voltage might sag as a result of the starter current. No problem - the GRT gear has stable power available on Power 2 input so they don't even blink during the start. Once the engine is running in a stable fashion the alternator is recharging the Essential Bus Battery and the GRT gear is taking its power from the main bus on the Power 1 input.

Now when things get gnarly and the main bus poops out, the poor pilot doesn't have to do a thing but keep on flying. The GRT gear auto-magically takes its power from whichever power input has the higher voltage. Since the main bus has gone kaput, the Essential Bus has the higher voltage to the GRT gear takes its power from the Essential Bus Battery.

This really is a simple system and very worthwhile to have in the aircraft, especially as you've discovered the hard way!
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Old 12-25-2020, 12:40 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,650

The suddenness of the event needs to be explored. It did not sound like some of the alternator or battery issues we've read about on VAF.

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Old 12-25-2020, 01:06 PM
BobTurner BobTurner is online now
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,165

Others have pretty well covered your questions.
Yes, you should set your GRT to alarm if buss voltage is less than 13.8 or so. Alternator is not working.
Yes, the GRT can display alternator output current. It uses a Hall effect sensor that they sell. Look for a green colored ring about 2” in diameter, with the heavy duty alternator output wire going thru it. Or perhaps the builder did not install it.
Others have described secondary power inputs for the efis. Or you may have a backup mini-efis with its own battery?
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Old 12-25-2020, 01:35 PM
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Tankerpilot75 Tankerpilot75 is offline
Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 586


We all make “mistakes” and if we’re lucky survive to add them to our bag of “experience.” Once you’ve discovered what caused you power failure and have addressed the issue, I strongly recommend you take some serious time to better learn your panel and EFIS system. Of course the best place to accomplish this is sitting on the ground with the engine off, few distractions, manuals in hand along with viewing a few UTube videos. GRT has some excellent videos on its website that will help.

As you’ve discovered understanding “buttonology” is an important skill and unfortunately takes time and practice - especially with the GRT EFIS system and it’s exceptional capabilities. Aircraft batteries don’t like this so I recommend you “invest” in a cheap external power supply.

I purchased mine on Amazon - a 110v to 12v, 25amp power supply for under $40 along with a power cord and wired alligator clips. I use it quite often to power up my avionics (EFIS, autopilot and Garmin 430s) for just this “learning purpose.”

I connect the external power supply (positive lead) to my panel’s main 70 amp circuit breaker (negative lead to aircraft ground terminal) using the alligator clip wires. This powers the panel without having to turn the battery on allowing me all the time I want to practice GRT and Trutrac Autopilot “buttonology” and improve my 430 data entry skills.

IMHO, having and using an external power supply to learn and practice your buttonology is critical to flying a safe IFR EFIS equipped aircraft.
Jim Harris, ATP, T38, EC/KC-135A/E/R, 2008 RV7A, 2nd owner, N523RM (2015)
Superior XPIO-360, Hartzel CS prop, Aerotronics panel with Dual GRT Horizon WS, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level, Electric trim, Tosten 6 button Military Grips, FlightBox wired to WS, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
Retired - Living the dream - going broke!
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Old 12-25-2020, 02:10 PM
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Roadjunkie1 Roadjunkie1 is offline
Join Date: Jun 2017
Location: Erie, Colorado
Posts: 84

Glad the outcome was a good one and a learning experience for you and all of us. That is one of the purposes of this group: learn from the mistakes of others; you don't have time to make them all yourself...! Yeah, time to stare at those glass screens for a while in a quiet hangar....

I've been over The Rocks to your airport. Can be an interesting ride even on a good day. Mountain flying is a different breed of animal, even in our capable aircraft. And in the dark (inside AND out)? Yikes! Are there ever anything but crosswinds at KAEJ?

Happy Holidays, All.....

1946 J-3 Cub (since I was 21...!) Batteries. Huh. I've heard of those......
1997 RV-4 SN 2860 (slow-built)
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Old 12-25-2020, 02:14 PM
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Roadjunkie1 Roadjunkie1 is offline
Join Date: Jun 2017
Location: Erie, Colorado
Posts: 84
Default Electronics: DYI as opposed to a "shop".

These are pictures from a previous thread from an RV-10 that was "professionally" wired at a shop. I agree that asking around and having someone help you who has done their own RV can be a much better option.....
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Old 12-25-2020, 03:06 PM
JDA_BTR JDA_BTR is offline
Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,215

Your battery was fully discharged but may be okay. Depending on the vendor there are battery conditioners that can bring it up to speed without getting a new one. Even if you get a new one make sure you have the charger that the battery specs call out as okay - it does matter.

I also disagree that bus voltage is an acceptable way to monitor alternator function. Seeing alternator current with an ammeter is tried and true. It is cheap and easy too. Most planes I have flown had some form of alternator failure light and/or an ammeter. Most didn't have a voltage readout.

The thought about the fuse-link blowing when you turned on a lot of load on low battery - possible. Most of them can take a lot of current though (60-80A). I wonder if you have a fuse-link when you don't have a shunt? Most people have the two together.

What is the switch "ADI Emergency Power" in the upper right of your panel?
What is the "Engine" light for?
Ser 140142, RV-14A flying - N1463
Ser 83825, RV-8 building - N8638?
USN Ret, Urologist, AME, Repeat Offender

Last edited by JDA_BTR : 12-25-2020 at 03:14 PM.
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