Redundant Power Systems Architecture

[BoilermakerRV]

Would any of you using dual alternators or dual batteries be willing to share your system architecture? I'm laying out and analyzing a few different options and would appreciate the input of those who have gone before me. The questions I can think of right now are:

1) Is there such a thing as a dual alternator controller?
2) How do you detect a failure of one of the alternators\batteries?
3) What provisions, if any, do you have for power shedding in the event of a failure?

Thanks in advance!

[Bob Ellis]

1) Is there such a thing as a dual alternator controller?

For me SBY - OFF - PRI switch

2) How do you detect a failure of one of the alternators\batteries?

PRImary Alternator fail light

3) What provisions, if any, do you have for power shedding in the event of a failure?

Essential Bus that is powered by my Standby Alternator

My rationale/mission goals and system here if it helps

[crabandy]

I'm no expert, but I just went through the thought process myself. I decided to go with the Aeroelectrics Z13-8R

I am powering my EFII and G3X (Essentials to flight) off the EBus. I used a 2-10 switch for Master and Alt (down off, middle master, up master and alt) and a 2-10 for the next switch over for Ebus and Aux Alt (down off, middle Ebus, up Ebus and aux alt). Normal ops will be with the Ebus on (aux alt off) that way if a power failure to either the main bus or batt bus happens my Ebus will stay powered continuously.
Failure of the main Alt will be set by a low voltage alarm on the G3X, at which point I will switch my Aux Alt switch up to keep power to the Ebus and turn on the Aux Alt. If I want to load shed I just turn the master off.
I was originally going to go with the IBBS backup battery but at only 4 amp/hr it powers G3x for a little over 30 min. If I power my EFII as well its even less time. For about $300 more I can have 8 amps as long as my engine is running and I don't have to worry about battery maintence/service/replacement.

[roee]

Originally Posted by BoilermakerRV

Would any of you using dual alternators or dual batteries be willing to share your system architecture? I'm laying out and analyzing a few different options and would appreciate the input of those who have gone before me. The questions I can think of right now are:

Originally Posted by BoilermakerRV

1) Is there such a thing as a dual alternator controller?

You wouldn't want that. It would be a single point of failure that could take out both alternators, so it defeats much of the reliability benefit of having two alternators.

Originally Posted by BoilermakerRV

2) How do you detect a failure of one of the alternators\batteries?
3) What provisions, if any, do you have for power shedding in the event of a failure?

Thanks in advance!

If you're committed to having two batteries and two alternators, consider simply arranging them as two complete independent electrical systems, each having one battery and one alternator. Having the two systems independent and isolated from each other makes it astronomically unlikely that both will fail simultaneously.

Then, have a sufficient limp-home capability on each electrical system so that you could lose one entirely and still be ok.

And/or you could get more sophisticated and have a cross-connect between the two electrical systems that would be disabled in normal operation. You would only enable the cross-connect under certain very unlikely situations where you needed to power loads on one system from the other. The design and operational aspects of this configuration though do get pretty involved, so I wouldn't recommend it unless you're committed to putting in the work and substantially educating yourself on the subject. Done improperly, you can get yourself in all kinds of trouble in unexpected ways.

Anyway, I don't want to assume, but if you're asking about dual batteries or dual alternators, then it sounds to me like you have a lot more homework to do before working out the details of any type of architecture. Your architecture selection first and foremost should be driven by your operational requirements, so a more formal requirements analysis would be a good start.

[Mike S]

I have a dual alternator, dual battery setup in my 10.

The system is setup like this-----main battery Odyssey 925 charged by 60A alternator (and assorted switches, breakers, lights and regulator etc) and the aux battery is a Odyssey 680, charged by a SD8 (again with necessary stuff).

I have a Schottky diode that allows current to flow from the main buss to the aux buss. This is unswitched and automatically allows current to flow from the main to the aux anytime the master is on.

My aux buss supplies power directly (through breakers) to the dual GRT EFIS screens, AHRS, magnetometers, and the radio stack. These are the things I consider as minimum equipment for safe flight.

The balance of the electrical load is hooked up to the main buss through the normal setup of breakers and switches.

I do have a battery cross tie contactor in case I run down the main batt, it parallels the two batteries to (hopefully) be able to start the engine. Of course if I have run down the main batt trying to start the engine, I suspect that the aux battery is not going to do the job either, until I correct the condition causing the non start.

I can turn on either the main, or aux battery switch, and the EFIS and radios are powered up. If both switches are on, I can turn off either and the EFIS/radio never misses a beat.

Starting procedure is to engage the Aux power until the EFIS comes online, and I have oil pressure and fuel pressure indicators working. Then I turn on the Main power, and start the engine. The starter load is isolated from the EFIS power, so the screens do not brown out.

I have an indicator light for a failure of either alternator, and can shut off either power feed as needed if there is an alternator fault.

If I had the magic Horton power, I would make up a nice drawing and post it, but sadly I do not

[rleffler]

I have dual alternators and batteries in my RV-10 as well, except I have a VPX/Pro which monitors everything. I can bring one battery online (either one) and I have a switch that ensures online that one alternator is online at a time. One circuit is the primary electrical system and the other functions as an e-buss. The vp/x gives you plenty of options on how to address redundancy and how you power shed.

[terry.mortimore]

Hi Michael.

I'm using the Z14 version of the dual alternator/dual battery set ups. I downloaded my copy from the B&C website.

http://www.bandc.biz/pdfs/001507Z14RevB.pdf

You'll see the z12 and z13 drawings there as well. I believe AeroElectric Connection is the source for these. If you have not seen Bob Nuckolls book on the subject it is worth tracking down a copy.

Cheers Terry

[jjconstant]

I started out by educating myself with Bob Knuckoll's AeroElectric Connection. It took me several times through it to start getting it, but I was a complete newbie. I gravitated towards the single alternator, dual matching battery architecture, but I always resisted the E Bus concept. Every time I tried to decide what would be on the bus, I would think up scenarios and the EBus would change. It got frustrating because every time I scrapped one set of things on the EBus I would say to myself "why not just turn off the non-essential loads with switches, based on the need at the time, like I was taught?" I talked it through with Stein at Stein Air -- he spent A LOT of time holding my hand talking through the various scenarios and when I came to the conclusion of just using the switches, he was more than fine with that. (Thank you again Stein!)

The concept I wound up with was to make it much like what I trained in, but with redundancy. Single alternator, single battery concept but with two identical batteries, two battery masters and two switches. I fly with one battery in the off position so I fly and operate like the simple systems I learned on. I alternate which battery I use. I will alwas have one battery with a full charge even if I somehow miss the big red light that tells me the alternator is off line and I have eaten into the reserves on the first battery.

[John Clark]

Originally Posted by roee

And/or you could get more sophisticated and have a cross-connect between the two electrical systems that would be disabled in normal operation. You would only enable the cross-connect under certain very unlikely situations where you needed to power loads on one system from the other. The design and operational aspects of this configuration though do get pretty involved, so I wouldn't recommend it unless you're committed to putting in the work and substantially educating yourself on the subject. Done improperly, you can get yourself in all kinds of trouble in unexpected ways.

"Unexpected ways" is what causes a lot of grief. I have flown several multi buss, multi alternator airliners that, we learned in training, had "gotchas," the ability to trash the part that was still working by throwing a few switches. The big issue is knowing what failed before applying a fix. Even in my Beech Baron it was easy to wipe out both alternators after some types of failure. Use care desigining the system and learn where the traps are.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

[BoilermakerRV]

So here is a first cut of a functional block diagram for a proposed dual alternator, single battery electrical system.

https://docs.google.com/file/d/0B1Z5...it?usp=sharing

Thoughts are appreciated.