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Dual Battery or Alternators?

amaris

Well Known Member
As I'm diving into the electrical system planning, I've started seeing issues with reliability on both the Plane Power alternators (this may have been addressed since some of the threads were older) and the Odyssey batteries. I bought the FFW kit from Van's so I've got both of those items. (haven't bought the battery yet but mounted the tray already).

I'm a fairweather VFR day flyer and building my plane with that in mind, but will have a G3X, a G5 (or similar) back up w/ battery, VPX and dual Emags. I do plan to pilgrimage to Osh at least one year and possibly some other longer flights so the idea of getting stuck at some remote airport seems plausible.

I see it as a BU alt will keep me flying on reduced load if my primary craps out but if my battery goes offline, I'll be landing quickly.

What are the odds of the battery completely destructing to the point of effectively not enough current to power anything vs the PP going offline?

I'd love to hear some thoughts from the group. I'm just starting to get into electrical and have been reading up, but still unsure about the architecture that's best.
 
SNIP
What are the odds of the battery completely destructing to the point of effectively not enough current to power anything vs the PP going offline?
SNIP

A properly maintained, modern battery that has not been abused is the most reliable component you can put in your airplane.

But - the same cannot be said for the components to get power from that battery to where you need it. This drives the thoughtful, dual battery design for modern, glass IFR aircraft, and why I find dual battery designs more tolerant when stuff goes south over single battery, dual alternator schemes.

For VFR, assuming you have steam backup instruments, this is not as critical. Be careful on relying on backup batteries like you mention for your G5 and G3X. Do they have the capacity to keep the panel up to fuel exhaustion?

For me, two PC-625 batteries and no other backup batteries are used in the all three RVs I built (dual SkyView IFR installs).

PM me your email address and I’ll provide details.

Carl
 
One can debate the merits of battery and alternator schemes till the cows come home but the one that will get you home from lands faraway where repairs can be done without interrupting a trip and thats the dual alternator, dual battery setup.
 
Never say never... I guess its possible for a battery to go bad in flight, but a bad battery usually tells you it's bad before you get to the taxi way.
A Battery if treated well just sits there.
An Alternator can take a battery out if it over charges it. Can also take it out if it undercharges it. Belt, bearings, brushes, diodes, regulators, wiring, switches can cause failures in alternator systems. If you have dual alternators (both mechanically wearing out at same time & rate operating or not), all these failure points are still there , times 2, you just hope failures don't happen at the same time.
Reasonable instrumentation should tell you when you are having a failure event, protection like Hi & Lo voltage alarms & overvoltage crowbars would be recommended in even the most modern EFIS monitoring systems.

This subject rivals "primer" & "which RV model?" for the volumes of opinions postings.
 
I think I'm looking for the ability if something goes wrong to be able to fly 30 or 45 minutes to the next bigger airport where I have a chance to get something fixed or replaced instead of being forced into landing and the closest runway.
The idea of being able to fly on until I'm ready for a refuel is appealing or continue the mission, but I don't think I'd trade adding a lot more complexity and cost for that option if it doesn't make sense.

The smaller bu battery on the G5 and G3X would be an emergency all else has failed scenario and not relied on for anything other than to hopefully give me some guidance while I'm landing asap.
 
Batteries seem to die slowly but alternators just die instantly! I have dual batteries and dual alternators. I’ve lost an alternator (PlanePower) and not terminated the flight and I’ve lost a battery and not terminated the flight. Both alternators are different brand and both batteries are different brand! Call me cautious!
 
Makes sense. I was looking at the B&C BU and thinking an EarthX to counter the PP and Odyssey.
 
Dual battery or alternator

Since you are only VFR you really don’t need a second battery or alternator since you do have a G5 with a backup battery. Your efis will alert you if your alternator fails and you are on battery power which will easily last you a half hour allowing you to land. You’ll know when your battery is failing when it becomes harder for it to turn over the engine. However it is real convenient to have a backup alternator if your main alternator fails allowing you to continue your flt to and/or from your destination. I would install a backup alternator before adding a second battery because the alternator is providing power while flying. Your battery is there for starting your engine and providing backup power if an alternator fails in flight. Plus your G5 has a backup battery so you easily have your six pack info to land other than loosing your radio if your battery fails before you have time to land for some extreme reason however you hopefully have a checklist to shed all nonessential power as soon as your alternator failed so you don’t find yourself in that predicament. Most likely you have an iPad for navigation as worse case. If you have a backup alternator the chances of having both alternators failing on the same flt would be very very rare. Scenario: you are 3 hrs from home late in the day on the weekend. Your alternator fails and you chose to have a dual battery instead of a backup alternator. You most likely won’t be making it home and might have to spend the night. With a backup alternator no problem. An additional cheap convenience is to carry the Earthx jump start battery to make sure you are able to start your engine if you are away from your home airport. Just my opinion
 
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I travel quite a bit and a fair amount of IFR, single bat with dual B&C alternators is what I run. Approximately 2000 hrs over 15 years with no issues and never needed the bu alt.
 
Firm believer in Dual Batteries

If I have dual alternators and one fails, I personally would head straight to the nearest airport to check things out. Look for the cause of problems like smoking wires, burnt belts, smoldering armatures etc, etc. I definitely would not intend to just press on feeling relief because I have more than one Alternator on board, NO NOT ME. But after I land and look things over it is most likely that second battery is going to be the most useful. Two or more Alternators will never start my engine, but that back up battery just may do it. If wired separately with it's own solenoid and secondary master switch its like having built in jumper cables with no loaner car in site. turn one battery on / turn other battery off. And now there are alternatives if concerned about weights (been there / done it on remote Little Tangier Island, Virginia). "Love Living on the Eastern Shore" Ed:D
 
Dual Alts etc

Spot on Walt!!
Post #3 also is more to the point for us down under - we don’t have FBO’s everywhere in ‘outback’ country so an Alternator or belt failure etc have real consequences when far from service centres. Not normal to carry spare Alt, belt & torque wrench just in case it’s needed.
Same applies when talking about fuel range, IF & when/where Avgas is available it can easily cost $14/us gal. That’s why I also talk about having extra fuel capacity (at least the plumbing in place) for many who wish to travel this wide brown land 😉
 
Dual Alts etc

Spot on Walt!! Applies to VFR here as well.
Post #3 also is more to the point for us down under.
We don’t have FBO’s everywhere in ‘outback’ country so an Alternator or belt failure etc have real consequences when far from service centres. Not normal to carry spare Alt, belt & torque wrench just in case it’s needed.
Same applies when talking about fuel range, IF & when/where Avgas is available it can easily cost $14/us gal. That’s why I also talk about having extra fuel capacity (at least the plumbing in place) for many who wish to travel this wide brown land 😉
 
Aeroelectric site, book, and mailing list

There are some great resources available here where this is discussed throughly.

http://www.aeroelectric.com

As others have said, batteries are very reliable, but keep in mind that issues affecting the battery can come from other places, like grounds, contactors, crimps, etc. These are discussed regularly and mitigations are suggested. As with many things in aviation, it comes down to good design, implementation, and maintenance. Electricity is magic, but keeping it flowing correctly in your RV is not! :)
 
My vote is for a backup alternator before a backup battery (a reservoir).

The backup alternator can supply a lot more power (over time) to complete a long cross country flight, while the battery is held in reserve for high draw things like lights and transponder. A battery always has a somewhat of an unknown condition and therefore an unknown and finite capacity, good for staring the engine, but not as good for indefinite supply of electrons.

Bevan
 
Keep in mind that likely 90% of us did our training in a bare bones Cessna 150. There are hundreds of champs and cubs that have NO electrical systems and use handheld radios when required. An iPad will give you nav capabilities that we could not have dreamed about a dozen years ago.
If your mission is as simple as you describe then save your money, WEIGHT and complexity and go with a simple system, one that can be repaired at any airport.
Carry a handheld radio and a basic tool kit and you will likely be able to solve most issues yourself.
If after flying for a while and you feel the need for more stuff it can be added. Make allowances in your panel for upgrades as required.
 
I think I'm looking for the ability if something goes wrong to be able to fly 30 or 45 minutes to the next bigger airport where I have a chance to get something fixed or replaced instead of being forced into landing and the closest runway.
The idea of being able to fly on until I'm ready for a refuel is appealing or continue the mission, but I don't think I'd trade adding a lot more complexity and cost for that option if it doesn't make sense.

The smaller bu battery on the G5 and G3X would be an emergency all else has failed scenario and not relied on for anything other than to hopefully give me some guidance while I'm landing asap.

Given your VFR only mission, I would argue that it should be relatively easy to land your plane with little or no DC power if you have a G5 with a BU batt, assuming your skills are sharp and you understand how RPM affects the Pmags power generating ability. If you take care of and test your battery and properly shed load in the event of an alt failure (assumes you have a volt gauge to determine this), you should have no issues getting 30 minutes of use from that battery.

Larry
 
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Backup alternator and EarthX "jump-pak" are

my choices -- I test the B/U alternator, periodically, by shutting down the primary (old original Suzuki?, external regulator). I carry a EarthX jump-pak (picked up at Sun n Fun) for the dead-battery issue. I have never had to use any of the backups on my plane, but the jump-pak has been used on several cars and other planes. Bought another jump-pak for the car -- wife has used it twice, on friends' cars.

Ron
 
I agree -- I test the B/U alternator, periodically, by shutting down the primary. I would rather replace the primary at home rather than traveling. I do have a G5 with it's small backup battery. The Garmin G3 system is also backed up by the TCW 6AH integrated backup IBBC. Main Battery is Earth-X 900.

Adding the a Earth-x Jump Start kit to the survival kit would be handy on remote trips with limited support.
 
I run a single oversized battery (EarthX 900 vented) with dual alternators here. I test the backup alternator on just about every flight, typically I'll cut off the primary and run on the secondary for at least half of every cross country, so they both get a fair bit of time.

An alternator is likely to fail in flight versus failing on the ground. A battery is likely to fail on the ground as versus in flight. I have had a few occasions where I turn on the master on an airplane and nothing happens - I have never yet had an occasion where I started the airplane and the alternator did not come online.
 
Well sure seems there are essentially 2 camps out there. Dual battery or dual alternators. All of your responses and logic make me think if I only read your response, you could convince me of going with your way.

Keep sending your thoughts, much appreciated!
 
Keep in mind that likely 90% of us did our training in a bare bones Cessna 150. There are hundreds of champs and cubs that have NO electrical systems and use handheld radios when required. An iPad will give you nav capabilities that we could not have dreamed about a dozen years ago.
If your mission is as simple as you describe then save your money, WEIGHT and complexity and go with a simple system, one that can be repaired at any airport.
Carry a handheld radio and a basic tool kit and you will likely be able to solve most issues yourself.
If after flying for a while and you feel the need for more stuff it can be added. Make allowances in your panel for upgrades as required.

Ditto. Since the original poster specifically indicated day VFR, my vote would be KISS, one battery and one alternator (so long as that one alternator is not a PlanePower :eek:) with iPad and handheld radio backup. Not much that you couldn't do that you would need to do with that combination, especially if you have a glass screen with a backup battery.
 
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I was going to upgrade my 7A to IFR a year ago but never did due to nearly at retirement age and didn't want to spend that much. During my extensive researching of the bat/alt subject I kept ending up with the extra battery as the best and safest route. I concluded that in IFR conditions with an alt or battery failure, a second battery ALREADY has everything I need to not loose control of this plane. No moving parts etc. The alt on the other hand has moving parts, is dependent on a the engine AND it has to make what a battery already has....
the electrical energy. I was also going to equip with the small stand alone G5 with it's own battery power. Then if you're the guy that's really ticked of the Gods of flying you have one last trick to save yourself.... that small G5's third battery.
 
There is no substitute for dual batts and dual alts on dual buses. That’s what I have been flying for 9 years and 1200 hours of mostly IFR cross country flights. It’s a belts and suspenders approach and it provides a very high level of confidence. (That’s a Z-14 in Aeroelectric parlance)

With that said, the sweet spot on the RV10 in my opinion is dual alternators and a single battery. That is certainly case for a VFR cruiser but I’d extend that to IFR cruisers.

Why is that the sweet spot? Alternators, their controllers and mechanicals, will fail. Having a second one, even a little one, will not just give you backup but will get you to your original destination and back if desired. Batteries don’t suddenly fail. They definitely go bad over time and can go bad ahead of time if abused and improperly managed, but otherwise they are pretty much bullet proof and easily managed for high reliability.

The great benefit of dual everything is that one can ‘experiment’ with battery abuse and poor management without effecting one’s dispatch reliability. In other words, I’ve screwed up managing 3-4 Odyssey batteries before I learned to just read the owners manual and follow its direction. I now have total confidence in Odyssey AGM batteries and would not hesitate to run with only one well managed and maintained battery.

Battery management and maintenance: Old style lead acid, AGM, and Lithium batteries are all different and what is good for one can be deadly to another. Pick your technology, your brand and then follow the manufacturers direction to the letter. For Odyssey AGM it means:

Keeping it fully charged when not in use which in my case meant not connecting it to an EFIS with a clock that required a few milliamps to run 24/7. That minor, slow discharge meant that one of my batteries was always being slowly drawn down when not flying. Even for a plane flown 3+ times a month, this would slowly kill the battery (which I would then swap with the good battery and ruin that one). It doesn’t mean it requires a trickle charger unless not used for an extended period (many months-year) as specified in the manual.

Make sure your charging system charges the battery at 14.1 to 14.7 volts - not 13.9 which is fine for old style batteries. I had one controller set at 13.9 and the other at 14.5 for a variety of dumb reasons. The 13.9 charged battery would last for 2 years, the 14.5 for at least 4 years. It took a long time to figure that one out since I was swapping the good and bad batteries for other dumb reasons.

If you have to use a charger, use a charger designed for the battery chemistry or better yet, a charger specified in the battery owners manual. In particular, old trickle chargers will kill an Odyssey AGM pretty quickly.

You don’t need a battery load tester or other exotic equipment to check the status of an AGM battery. A simple volt meter will do the trick. First, charge the battery on a proper charger, let it sit off charger for 24 hours, then check the voltage with no load. If memory serves me, 12.8 volts means 100% okay, 12.5 means 75% and it’s time to change it out.. There is a chart in the owners manual with various voltages and battery capacity. There is also data on temperature adjustments to the voltage. But that voltage check, specifically on AGM batteries, is a reliable check on battery condition. I’m getting 4 years plus out of my small (790?) Odyssey batteries and I can run them down to 75% . A single battery might be best swapped out at 80 to 90% capacity
There’s a good case to be made for minimizing or eliminating backup batteries for specific avionic units. To be reliable, they need to be properly maintained. At best, just another maintenance item. At worse a maintenance item easy to ignore until after it fails. I’ve eliminated all of my backup batteries and rely on my main batteries. I would not hesitate to do the same with a single battery.
 
I've had car batteries suddenly go bad.

It's always been a cell that decided to short.


Just saying...............
 
In my lifetime I've had at least 3 batteries suddenly fail on various vehicles (so far not my RV). It's always an internal cell connector. You can measure the voltage across the terminals (open circuit) and read normal 12.7-ish and with any load it reads zero.
Two of those were Delco flooded batteries and one was a Wesco AGM.
 
Well sure seems there are essentially 2 camps out there. Dual battery or dual alternators.

Three actually -- the third being single battery, single alternator. That's the camp I'm in, for VFR anyway. More alternators / batteries / relays / wiring just makes for more cost, more weight, more complexity, more things that might fail. Batteries do fail but usually they give plenty of warning. Alternators do fail but if you have a good quality one it's pretty rare. Either way if you have magnetos and / or self-powered EI such as P-mag, the engine will keep running just fine without a functioning electrical system. If you have a handheld radio, a handheld GPS or old paper map and can manage to keep your head about you, an electrical failure (assuming no smoke) in VFR should be a non-event. Yes there is some "risk" of having to deal with a breakdown at an unfamiliar airport but we're talking about something that's pretty rare, plus that sort of thing can be an adventure all on its own!

Mind you I'm not advocating just blithely flying on with a failure, I'm just trying to make the point that there's redundancy already built-in for the things that really matter. You may or may not want backups for the critical instruments -- yeah I have 'em but it's my personal grumpy old-school opinion that if you don't feel like you can comfortably fly / land your plane without a GPS or even an ASI, more instruction is a better investment than more backups.
 
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Three actually -- the third being single battery, single alternator. That's the camp I'm in, for VFR anyway. More alternators / batteries / relays / wiring just makes for more cost, more weight, more complexity, more things that might fail. Batteries do fail but usually they give plenty of warning. Alternators do fail but if you have a good quality one it's pretty rare. Either way if you have magnetos and / or self-powered EI such as P-mag, the engine will keep running just fine without a functioning electrical system. If you have a handheld radio, a handheld GPS or old paper map and can manage to keep your head about you, an electrical failure (assuming no smoke) in VFR should be a non-event. Yes there is some "risk" of having to deal with a breakdown at an unfamiliar airport but we're talking about something that's pretty rare, plus that sort of thing can be an adventure all on its own!

Mind you I'm not advocating just blithely flying on with a failure, I'm just trying to make the point that there's redundancy already built-in for the things that really matter. You may or may not want backups for the critical instruments -- yeah I have 'em but it's my personal grumpy old-school opinion that if you don't feel like you can comfortably fly / land your plane without a GPS or even an ASI, more instruction is a better investment than more backups.

Yes, I’m of the same camp. The big thing is to make sure that a single failure won’t be catastrophic. If you’re running on a single alternator, you need to ensure that if it fails, you have enough battery capacity to get somewhere where you can safely land. Problems are much easier to deal with at zero knots ground speed!
 
4 camps

dual alternators and dual batteries


Although you could go with less capacity (weight) in each.
 
Week ago a neighbor asked me to help him diagnose an electrical problem on his Starduster. He heard a loud pop while cranking and as it turned out, one of the battery cells shorted. They do fail instantaneously.
 
Yes, I’m of the same camp. The big thing is to make sure that a single failure won’t be catastrophic. If you’re running on a single alternator, you need to ensure that if it fails, you have enough battery capacity to get somewhere where you can safely land.

Assuming you have some combination of magnetos and self-powered EI, a working battery is not essential to the safe completion of a flight either. I believe it's important to cultivate that attitude so that if it happens it doesn't unnecessarily become a panic situation.
 
Assuming you have some combination of magnetos and self-powered EI, a working battery is not essential to the safe completion of a flight either. I believe it's important to cultivate that attitude so that if it happens it doesn't unnecessarily become a panic situation.

Perhaps VFR, but not IFR.

Carl
 
Keep in mind that likely 90% of us did our training in a bare bones Cessna 150. There are hundreds of champs and cubs that have NO electrical systems and use handheld radios when required. An iPad will give you nav capabilities that we could not have dreamed about a dozen years ago.

^^^This

All my time is in various pre 1981 172s. Steam gauges, VOR, LORAN-C (you know you remember that one :cool)... And our current 172 is snazzy for its breed with dual G5 and GFC500 autopilot. And all on 1 alternator/ 1 battery.

I’m strongly leaning 2 alt/ 1 battery for the 14 were building, but a guy in a 8 stopped by the FBO recently and made a really strong case for a 1 alt/2 battery setup.

Either way you go, you will most likely be equal to or greater in capacity and flexibility than what you were trained in. Ok, maybe not you military guys and gals, but us civilians will have the best setup we’ve ever had.
 
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Things to also consider:

How many amps are you consuming after losing your only alternator? In the RV-10, I calculated about 5 amps with minimum instruments required. With a 22 amp hour main battery, 6 amp hour IBBS battery, and the backup G5 (with its own 4 hour BU battery), I'll most likely run out of fuel before running out of complete battery power. Agreed that this is not including lights, flaps, pitot heat, fuel pump etc...

IMHO, losing a main electrical system whether a battery or alternator in flight would require a landing at the nearest suitable airport no matter your setup.

Battery failure in flight:

turn off the battery and run off alternator power, land at nearest suitable airport

Alternator Failure in flight:

Turn off alternator, monitor voltage, if extended time required, turn off battery or avionics depending on wiring diagram (running off of IBBS), turn battery back on for approach and landing for flaps, fuel pump, etc..., land at nearest suitable airport.

Back to the OP, KISS method, one alternator, one battery, and one IBBS for critical systems. Especially VFR...

By all means, I'm no expert and would like to hear everyone's thoughts.
 
Arguing dual batteries vs dual alternators seems to me to be a pedantic exercise when you can have both options with minimal weight increase. An alternator weighs 6 lbs as does an EarthX battery. Artful and careful planning of such a system will give you redundancy that is robust. I’m not sure it’s necessary for a VFR aircraft but an IFR aircraft with electronic ignitions and fuels systems lends a certain degree of necessity for electrons to keep flowing. No system will be 100% foolproof as others have said before.
 
Not to beat a dead horse, but the issue is not just two batteries, it is system design.

If you are using backup batteries, IBBS or whatever and a single ship battery you could just eliminate all those with two identical ship batteries and a thoughtful design (two batteries in parallel or common connection points violates this rule).

Design objective: “no battery is just along for the ride”.

Carl
 
Not to beat a dead horse, but the issue is not just two batteries, it is system design.

If you are using backup batteries, IBBS or whatever and a single ship battery you could just eliminate all those with two identical ship batteries and a thoughtful design (two batteries in parallel or common connection points violates this rule).

Design objective: “no battery is just along for the ride”.

Carl

Yup...the system design is important. I never meant to say it wasn’t. Nuckolls seemed to think it was a viable option in his Z14.
 
As the OP on this thread, I thought I'd follow up. After consultation with trusted pilots & builders, my decision is this; I've returned my PP alternator since that seems to be a real point of concern about the reliability at the moment. I've gone with a new IR auto alternator available at any auto parts store and will run a single ship battery. My G3X will have it's own BU battery and my G5 will also have it's own BU battery. Since I'm really a fair-weather VFR pilot and have no plans of IFR, I'm comfortable with the risk factors in this setup in that if I have an issue, I'll be landing at the nearest airport anyway. And hopefully, there's an auto parts store within a decent drive so I can replace my alternator.

Everyone seems to have a different take on this, so I appreciate understanding where I've landed. One guy's minimum may be dual battery/dual alts and another single alt, single battery, no backup.
 
Design your system.

Then keep tweaking it by adding all your possible bells and whistles (dual everything).


Then back off to what you need now. Leave some aspects of the full design installed (i.e. the spot where the 2nd battery will go, some holes for wire runs, spots for added switches, etc.)


Then you are in a position to add all the bells and whistles later without a redesign..............
 
Design your system.

Then keep tweaking it by adding all your possible bells and whistles (dual everything).


Then back off to what you need now. Leave some aspects of the full design installed (i.e. the spot where the 2nd battery will go, some holes for wire runs, spots for added switches, etc.)


Then you are in a position to add all the bells and whistles later without a redesign..............

Thanks, Ed. Good advice.
 
Everyone seems to have a different take on this, so I appreciate understanding where I've landed. One guy's minimum may be dual battery/dual alts and another single alt, single battery, no backup.


Yes, different people's intended use for their planes, different models, different levels of comfort witt failure scenarios. It's definitely not a one size fits all question. The beauty of this is that each of us gets to decide what's the best combination for ourselves and build it that way.

One consideration that hasn't been talked about much is WEIGHT. In a -10 that might not be so much of a factor but in a -7 the ounces add up and a battery adds a fair bit. A heavy -7 will still fly well but it limits your useful load and you will notice it if you do aerobatics. Personally I love my O-360 / CS powered RV-6 but I've also flown an O-320 / fixed pitch and the difference in how nimble it is is striking (albeit with a less-favorable CG envelope). That backup alternator adds less weight so if I were considering one or the other in anything other than a -10, it would push me towards that over an extra battery. On the other hand with that O-320 / fixed pitch, one might want a few extra lbs up font.

Anyway it sounds like you've taken the info provided and made your choice so good on you. I just wanted to add this bit as food for thought for others who might come along and read this thread.
 
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