Dual Battery or Alternators?

[rv6n6r]

Originally Posted by Papa

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.

[Carl Froehlich]

Originally Posted by rv6n6r

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

[Papa]

Originally Posted by Carl Froehlich

Perhaps VFR, but not IFR.

Carl

Exactly, I’d like my gyros (AHAHRS), navigation, and radios to keep working long enough for me to put it on the ground at a minimum. But that is very doable without getting overly complex or heavy.

[sloengineer]

Originally Posted by Tom Martin

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.

[rv6n6r]

Originally Posted by Carl Froehlich

Perhaps VFR, but not IFR.

Carl

Absolutely! I should have said that but thought it was implied since the OP is talking VFR.

[Cptnmat]

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.

[RandyAB]

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.

[Carl Froehlich]

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

[RandyAB]

Originally Posted by Carl Froehlich

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.

[amaris]

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.