[MS19087]

I am finalizing my power design. I have read lots of info (aeroConnections, etc). I'd appreciate any comments - my plane is intended as a VFR X-country flyer. I am considering 2 options: dual battery (680s) w/ single 60A alt OR dual alt (60A + SD8) and single 680. Besides the obvious price vs weight considerations - can anyone offer strong reasons to go one way or the other? Thanks!!

 

[scard]

The dual alternator route is super easy to build.

 

[LifeofReiley]

If you've been to one of Bob's Seminars, one alt is all you'll ever need. Build your system for the endurance that makes you comfortable. Everything else is a waste of time and money... all electric airplane or not.

 

[Walt]

Dual Alternators..

Battery failure is super rare so why back it up A back up alt like the SD8 will let you continue your trip with a failed main alt as usual if you just keep the load light. I fly a lot a CC and have dual EI and run the BC40 and SD8.

 

[johnp]

dual alts/batts

thought about this a lot. i plan ifr, so my requirements are slightly different. few thoughts --

which is worse, an alternator fail or a battery fail? -- depends on the failure mode. if the battery just won't hold a charge, it's only a problem at start time (once you get it running, you are probably o.k.) but if the battery fails "open", then the alternator gets unloaded, overvoltage happens, and you either fry a bunch of stuff, or your "ov-protection" kicks in and the alternator goes off-line anyway. so dual alternators do nothing to help you in the case of this type of battery failure.

if the alternator fails, then you are limited to the juice left in the batter(y/ies) to complete the flight, or at least get you somewhere that you can get on the ground. depending upon the load, that may be anywhere from 20 minutes or so to maybe double that (assuming good condition of the battery and timely recognition of the problem). dual batteries would give you roughly double the endurance (assuming same capacity batteries.) so dual batteries help in both the case of the primary battery failure or the alternator failure. in addition, depending upon how you wire the batteries, you might be able to bring them both online for "extra cranking capacity" in cold weather.

the above analysis assumes single-point failures only.

i opted for dual batteries. if i were vfr only, i probably wouldn't bother (unless i did a lot of night flight.)

john

 

[DGlaeser]

Why 2 for VFR?

Will you have an electrically dependent engine? If so, then dual power is warrranted (I went with dual batteries, one alternator). If not, why bother? The battery will probably power your instruments and radios longer than your fuel will last if the alternator quits . . . And it's the lightest, cheapest solution as well

 

[LifeofReiley]

thought about this a lot. i plan ifr, so my requirements are slightly different. few thoughts --

which is worse, an alternator fail or a battery fail? -- depends on the failure mode. if the battery just won't hold a charge, it's only a problem at start time (once you get it running, you are probably o.k.) but if the battery fails "open", then the alternator gets unloaded, overvoltage happens, and you either fry a bunch of stuff, or your "ov-protection" kicks in and the alternator goes off-line anyway. so dual alternators do nothing to help you in the case of this type of battery failure.

if the alternator fails, then you are limited to the juice left in the batter(y/ies) to complete the flight, or at least get you somewhere that you can get on the ground. depending upon the load, that may be anywhere from 20 minutes or so to maybe double that (assuming good condition of the battery and timely recognition of the problem). dual batteries would give you roughly double the endurance (assuming same capacity batteries.) so dual batteries help in both the case of the primary battery failure or the alternator failure. in addition, depending upon how you wire the batteries, you might be able to bring them both online for "extra cranking capacity" in cold weather.

the above analysis assumes single-point failures only.

i opted for dual batteries. if i were vfr only, i probably wouldn't bother (unless i did a lot of night flight.)

john

Good thoughts John... and you can build in an Endurance factor that will out last most bladders without a second alternator at a fraction of the cost. I need to come see your project sometime soon. Projected flying date?

 

[erich weaver]

If you've been to one of Bob's Seminars, one alt is all you'll ever need. Build your system for the endurance that makes you comfortable. Everything else is a waste of time and money... all electric airplane or not.

Hmmm. I dont have that impression at all. Bob's book and his posts on Aeroelectric list highly recommend the Z-13/8 architecture, which includes the SD-8 backup alternator. Failed alternators do seem to crop up in the discussions here on VAF, so they do occur. Given an inoperable main alternator, a true "Nuckollhead" would want to continue the flight so that endurance is limited only by fuel onboard, not the capacity of the battery, which may not be easily quantifiable in terms of distance or time left. The SD-8 backup will allow this, and is practically bulletproof. Piece of cake to install as well. Inflight battery failures seem to be almost unheard of.

erich

 

[tc1234c]

single 40A IR alt w/ dual 680

I built my 9A with single alternator and dual battery. My mission is cross country and so far I have had a few hours in IMC. My rationale is exactly the same as John P. Each of my 680s is controlled by a master relay. I always turn both on (Master and Aux) at start up. In case of alternator failure I have enough juice to land safely in an airport of my choosing.

 

[LifeofReiley]

Hmmm. I dont have that impression at all. Bob's book and his posts on Aeroelectric list highly recommend the Z-13/8 architecture, which includes the SD-8 backup alternator. Failed alternators do seem to crop up in the discussions here on VAF, so they do occur. Given an inoperable main alternator, a true "Nuckollhead" would want to continue the flight so that endurance is limited only by fuel onboard, not the capacity of the battery, which may not be easily quantifiable in terms of distance or time left. The SD-8 backup will allow this, and is practically bulletproof. Piece of cake to install as well. Inflight battery failures seem to be almost unheard of.

erich

I went to another of Bob's seminars just two weeks ago and the schematics in the book, which are many, are examples only. For a VFR plane, there is no reason at all for dual alternators. You build in an endurance factor (time on the endurance bus) that suits your needs... ie calculate and build to your endurance bus. This is the information we recieved in Bob's lecture. I tend to believe him.

I never said that there was not a place for dual alternators. How many RV'ers are flying hard IFR? I don't have the answer.

 

[erich weaver]

The battery will probably power your instruments and radios longer than your fuel will last if the alternator quits . . . And it's the lightest, cheapest solution as well

Bob Nuckols' ears have got to be burning on this one. I respectfully disagree on both statements. How many of us really have a good handle on how long their existing (used) battery will last without an alternator on a given flight? You cannot rely on the amp-hour rating of a battery, because the actual hours will vary depend on the amps - and its not always a linear relationship. Furthermore, the rating is for a band new battery - they certainly dont get better with use/age.

And a PC-680 battery is certainly heavier than an SD-8 backup alternator, no?

erich

 

[FlyerJumper]

Yet another thought...

We're no where near flying yet, but currently our thinking is the dual battery/single alternator route. We plan an electrically dependent aircraft, so we consider dual one-or-the-other a high priority. We decided against dual alternators because (assuming no severely life shortening defects) once one is at the point that its thinking about quiting, the other one is just as old and will be required to shoulder the load. May be no big deal, but we liked the idea of rotating one of the batteries out at each annual (neither battery older than 2 yrs). That way, if it ever came down to needing backups, we were depending on newer equipment rather than older.

 

[Frank N821BF]

Dual Battery

We have dual 680's in our 9A, we do alot of night flight. We have dual Lightspeed EI's, only one EI is connected to each 680. The chance of losing both 680's or the chance that the 680 that dies is connected to the only good EI is so small that I'll win the Lotto first. We did have an alternator failure over Pontiac one night going home to Lapeer. The warning came up on our GRT EFIS that the charging system had failed, we continued home(20 min.) watching both of the battery voltages. We did not turn off our LED nav lights or strobes, used our landing lights at Lapeer and still had 12.4vdc on both batteries.

Frank
Lapeer, MI
N821BF

 

[LifeofReiley]

We have dual 680's in our 9A, we do alot of night flight. We have dual Lightspeed EI's, only one EI is connected to each 680. The chance of losing both 680's or the chance that the 680 that dies is connected to the only good EI is so small that I'll win the Lotto first. We did have an alternator failure over Pontiac one night going home to Lapeer. The warning came up on our GRT EFIS that the charging system had failed, we continued home(20 min.) watching both of the battery voltages. We did not turn off our LED nav lights or strobes, used our landing lights at Lapeer and still had 12.4vdc on both batteries.

Frank
Lapeer, MI
N821BF

Exactly what I'm talking about. Endurance built in... Better than a cheezy SD8 alternator, can't keep up with feeding one dead battery and you can forget about it doing anything for two batteries.

 

[Freightpilot27]

Dual Alternators, One Battery

In 9 years and 8700 Hours of FAR 135 (1/2 piston, 1/2 turbine) I have had ONE battery "runaway" failure and more than a dozen alternator/generator failures. the Battery failure caused an over heat condition but, for the most part, did not effect any aircraft systems in flight.

I am most definitely planning a dual alternator, single battery. Both alternators will have some load at all times and each will be able to power either main buss in the event of an alternator failure. Obviously i will have to load shed if the main 60A alternator fails and im left with only the secondary 20A. (I am planning this either with a single switch or automatically)
However, my mission profile is slightly different with dual EFIS, autopilot, Plasma III, everything except TKS. (Solid, redundant IFR)

I am not understanding why anyone would need dual batteries or dual alternators for day or night VFR? Or for that matter, even VFR, why someone would continue to rely on the battery only to continue a flight to destination (battery last longer then fuel)?

My 2 cents

 

[craigvince]

Dual batteries

So, those of you who have dual batteries, can you post some pics of your dual installation please? If no pics available, where did you mount them?

Thanks!

 

[rwtalbot]

Duel Alternators

Some may like to take a look at the diagram on aeroelectric.com which describes modifying the SD8 kit to allow it to operate in the event of a battery failure (http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z25L.pdf).

I intend to do this on my aircraft. This will virtually guarantee I can power the E bus in the event of even a double failure (either alternator and the battery). My engineis not electrically dependant but I do plan to fly night and IFR.

The SD8 is lighter than the extra battery and it will run indefinately while the engine is still turning. The battery will degrade over time and I would be quite concerned with only a battery after the main alternator failed in IMC.

I have already lost an alternator on a rented Piper in IMC. My engine kept running but anyone who thinks that the engine is the only issue is kidding themselves. The thought that my battery was still working did not make me feel a whole lot better. I am not having that problem again if I can help it.

Richard

 

[MCA]

Dual Batteries

So, those of you who have dual batteries, can you post some pics of your dual installation please? If no pics available, where did you mount them?

Thanks!

Both batteries are mounted on the firewall. There is a picture here: http://www.io-390.com/IO-390.com/Electrical.html

My CG is at the very forward limit, and I'm considering moving one or both to the back. Just need to do some CG calculations and testing first. For ideas, I looked at what the RV-10 guys are doing to mount their battery in the back.

 

[Walt]

Well for me personally...

it's not just a matter of "endurance" its a matter of "convenience". Yea sure I can make it to a safe landing with just the battery but it's more a matter of practicality than survival. If I'm 500 or a thousand miles from home and my main alt quits I don't have to find the nearest airport and AOG in a new alternator, find a place to stay and so on I'd rather just flip on the back up alt, turn off some stuff I don't really need and continue the trip!

 

[tc1234c]

One battery, two batteries, one alternator, two alternators, IR, ER, etc. have been debated extensively at many forums. I am not convinced there is a right answer to it. It all depends on the mission profile and personal priority (believe/bias).

If you shall decide to mount two 680s on the firewall, here is my example. The right side battery mount is per Van's instruction. The left side is shown in the picture. Since there is very little space to install/remove the battery (impossible to take the battery out from top), I stole the idea from Walter Tondu to use SS hinge to open the front part of the battery mount.

 

[LifeofReiley]

One battery, two batteries, one alternator, two alternators, IR, ER, etc. have been debated extensively at many forums. I am not convinced there is a right answer to it. It all depends on the mission profile and personal priority (believe/bias).

If you shall decide to mount two 680s on the firewall, here is my example. The right side battery mount is per Van's instruction. The left side is shown in the picture. Since there is very little space to install/remove the battery (impossible to take the battery out from top), I stole the idea from Walter Tondu to use SS hinge to open the front part of the battery mount.

Thanks Ted... I must borrow the same battery mounting idea.

 

[gmcjetpilot]

How about 1 + 1 = plenty good?

I do understand the IFR mission with all electronic flight instruments or an electrically dependant engine; you might need more electical redundancy with that mission. However I assume you are DAY/NIGHT VFR with a Lyc. ie, mechanical fuel pump, mechanical fuel system - carb / FI and at least one magneto. In this case one battery and one alternator is plenty.

Bob has a good book and his whole focus is on electical system. He has many advanced wiring architecture, schemes and philosophy, which are all good, but tend towards the complex and overkill in my opinion. The general wisdom that I subscribe to is:

Keep it light
Keep it simple
Stick to the Plans
One Bat + One Alt = good for most VFR RV's*
(*provided the engine does not need electrons to run, if you need redundant or independent power for the engine I prefer the dual bat + one alt, than dual alterantor.)

I would recommend a Plane Power internally regulated alternator for good QC, plus as a bonus you get the extra OV protection. Alternators do die. Batteries are very reliable and if you follow the preventive replacement of the battery, it should never let you down, unless you leave the master on after parking.

Look you are going to pay for all that redundancy with weight, for a very unlikely event. How much long cross country are you going to do? By long I mean +500 miles not 50 miles. DO YOU REALLY NEED THE REDUNDANCY? REALLY?

If your emergency electical load is down to a few amps, your battery should last longer than fuel range. You could fill up and fly a very long leg on battery only, conserving electical power. This is practical for day VFR. I know a guy with a RV-3 with no alternator. He flys on battery power and charges it up on the ground or with a solar charger.

Many have written about the heartache of losing their alternator on a far away cross country trip. Around the home field losing your Alternator is no big deal, land on battery power. However away from home, getting your alternator repaired can be a nightmare, especially if you have a custom alternator like a B&C. The PP and B&C alternators are reliable, but things do die. Preventative maintence like checking the brushes might save you grief on a trip.

A supplemental battery for handheld GPS is a good idea. A lot of guys have individual powered "GLASS", besides a handheld GPS or COM radi, Dynon Glass has an internal battery option. A GPS and held gives you you approx altitude, ground speed (approx airspeed), hdg and Nav. If you have all electronic ignition or FI that needs uninterrupted power, clearly a small second Aux battery might be useful and necessary for required redundancy.

In the old days with vac pump/pitot-static flight instruments, mechanical engine gauges, at least RPM and MP, you could fly all day with out an alternator. Turn the master off or the radios/lights and fly, as long as the airspace allows it. This is for day VFR of course.

I recommend you start with the idea on one good battery and one good alternator. The weight saving and simplicity will be a gift that keeps on giving. Most all cars I know of have one battery and one alternator and they go 100,000 miles with out an issue. If you do go with ONE + ONE, battery and alternator maintence is key to reliability.

 

[DGlaeser]

OK but ...

Bob Nuckols' ears have got to be burning on this one. I respectfully disagree on both statements. How many of us really have a good handle on how long their existing (used) battery will last without an alternator on a given flight? You cannot rely on the amp-hour rating of a battery, because the actual hours will vary depend on the amps - and its not always a linear relationship. Furthermore, the rating is for a band new battery - they certainly dont get better with use/age.
And a PC-680 battery is certainly heavier than an SD-8 backup alternator, no?
erich

If you follow Bob's philosophy, the whole idea of the E-Bus is to reduce loads enough that the battery will last as long as your fuel, and the battery is either replaced yearly, or capacity checked so you know if it is up to snuff. Why carry the weight of the second item (battery or alternator)?

 

[MS19087]

Thanks for all input . . .

Thanks for all of your input - inthe end, I agree that I need to be real honest with myself as to the type of flying I intend to do, etc. I fully endorse the KIS principle - I will likely stick with one + one, yet insure that Ihave made provisions to allow me to upgrade in the future should I decide I really need an additional power source.

 

[LifeofReiley]

If you follow Bob's philosophy, the whole idea of the E-Bus is to reduce loads enough that the battery will last as long as your fuel, and the battery is either replaced yearly, or capacity checked so you know if it is up to snuff. Why carry the weight of the second item (battery or alternator)?

Dennis,

You've hit the nail on the head! You've actually been to one of Bob's live seminars. And so it is...

 

[Pilottonny]

VFR, Night, IFR,......what about over water?

Hey George,

what about if you are going over a long stretch of water in your double electronic ignition, all electric instruments, plane? That may not be every bodies flying mission, but from where I live, a lot of destinations go across a lot of water (UK, Scotland, al the Scandinavian countries, Channel islands, Mediterranean, etc.). I have no idea how much ?electrons? are consumed by the two Electronic Ignitions?? But if the alternator quits and you know there is no way to land for the next couple of hours, your heartbeat is bound to go up! I guess you could switch one ignition off, to save battery power? (you obviously switched off all other stuff and are now flying on your Whiskey compass), but still, how long will the battery last? Did you notice the problem on time? Or has the battery already been drained 50% before you figure out what the problem is? Hey,?. the battery may already be down to 50% due to ?old age?.

Anyway, I was also thinking of some redundancy for my all electric plane (engine and instruments!) I am just not sure yet what it is going to be, but a back-up alternator, maybe even with a small battery of its own, is what I was thinking about. There are some more advantages to this setup than redundancy alone! You could use the back-up battery to program your GPS, set-up the instruments, chat with the tower, etc. without the engine running and not have to worry about your cranking power!

Anyway, I have not decided yet
.
Great thread!

Regards, PilotTonny

 

[Freightpilot27]

Keep one Mag

I think keeping one mag would be a great way to have redundancy with your engine. Loose your alternator and the engine will keep running even after your battery goes kaput.

 

[erich weaver]

If you follow Bob's philosophy, the whole idea of the E-Bus is to reduce loads enough that the battery will last as long as your fuel, and the battery is either replaced yearly, or capacity checked so you know if it is up to snuff. Why carry the weight of the second item (battery or alternator)?

Probably shouldnt waste any more of peoples time arguing about what Bob Nuckolls does or does not recommend, but this article from his web site speaks for itself:

http://www.aeroelectric.com/articles/allelect.pdf

The point here is that with the SD-8 and the e-bus, flight can continue indefinitely when the main alternator goes bad. If you do have the all-electric plane and truly change out your battery every year thats great. I doubt many really do that and Im even more confident that most of us would be only guessing about how long their existing battery will hold out given a main alternator failure. The Z-13/8 system makes the whole event a, well, non-event for a very modest weight gain.

And oh yeah - the SD-8 is NOT cheezy. So there.

kindest regards,

erich

 

[fmarino1976]

Dual Alternators...

I believe that the best advise is to keep it simple and light, so a single alt + single battery would be sufficient for most folks. But for IFR, and flights over water, and electrically dependant engines do require some degree of redundancy. I personally think that a dual alternator setup is the way to go. Batteries seldom fail, in fact, as a mechanic I have never seen a total failure of a battery, except for one on my truck that failed opened after it got a good hit on one if the terminal lugs. Batteries loose their ability to hold charge, and sometimes cell get shorted, but they don't typically cause the electrical system to fail completely. Alternators on the other hand do fail, they either quit charging altogether, their rectifiers burn out or get shorted (producing all kinds of electrical noise), or their regulators fail and could cause an overvoltage situation. Personally I would feel more confident running on my backup alternator rather than watching the battery voltage drop if I were to loose the main (or only) alternator in IMC. Also, twin engine aircraft designed for heavy IFR have 2 alternators/generators and a single battery.
There are talented people arguing in favor of the dual battery + 1 alternator setup, and I'm not trying to prove anything right or wrong, this is just my somewhat educated opinion, YMMV

 

[macrafic]

If you've been to one of Bob's Seminars, one alt is all you'll ever need. Build your system for the endurance that makes you comfortable. Everything else is a waste of time and money... all electric airplane or not.

Darrell, I attended one of Bob's workshops at Oshkosh this year and heard something quite different, ESPECIALLY for an all electric aircraft. I heard him say something that he had written me in an email; if he were to build an all electric plane today, the dual alternator and single battery would be the way he would go.

 

[LifeofReiley]

Darrell, I attended one of Bob's workshops at Oshkosh this year and heard something quite different, ESPECIALLY for an all electric aircraft. I heard him say something that he had written me in an email; if he were to build an all electric plane today, the dual alternator and single battery would be the way he would go.

You left out one part... Bob talks about cost of ownership a lot. If you have $500.00 to throw at a silly 8 amp alternator and want to justify this then do it. He also suggests buying a $38.00 battery once a year and tossing the old. There are still people paying over $100.00 for an PC680. Again, if you can justify this then do it. FYI, If you didn't catch on, Bob does assist in marketing products for many companies and he's good at it too. Nothing wrong with that!

I'm done...

 

[rracer10]

1 Battery + 1 Alternator + ????

Food for thought:
Similar to many of the posts here, but with a twist is Greg Richter's (from Blue Mountain Avionics) take on it. He says the KEY is going with a 24 volt system. If you haven't started you electrical system yet, this is definitely a good read. (ex. "Cars are twelve (12) volts, airplanes are twenty-four (24). There you go, easy enough.") He covers topics like "How many Batteries", "How many Alternators", "How many Busses", etc.

Link: http://www.bluemountainavionics.com/pdf/aircraft_wiring_04december2004.pdf

If anyone is familiar with Greg's approach and reasoning, could you share your experience.

 

[N787R]

Dual battery + dual alternator

Back up battery drives also internal lights. (I keep leaving them on sometimes and this way if the battery is drained, I can still start engine with the main battery).

Back up alternator. Because it is not always about emergency. It is about being able to continue flying (day vfr in this case) untill you get replacement.

Ben

 

[Sticky1]

Battery vrs Alt

I really do not understand what all the hub-bub is about.

All certified aircraft have a battery and an alt. Thats a good start......

If I am IFR and my batt goes bad, I would wish to have a second battery.

If I am IFR and my alt goes bad, I would wish to have a second battery.

I have a second battery that I can switch onto the buss anytime I want. I can also switch off the primary battery anytime I want. I can also charge both of them at the same time or have them on the buss at the same time.

In planes of this size I dont belive 24vdc systems are any better than 12 volt systems, in fact they are more of a pain in the *** when you need to jump it to get it started....

The cold hard facts are; If you are flying IFR (Worst Case) the rules say to land in emergencys....loosing an alt is an emergency. A 2nd battery will get you down with a full load because usally there is an airport within 20 miles. At least where I fly.....

 

[rv6ejguy]

Hey George,

what about if you are going over a long stretch of water in your double electronic ignition, all electric instruments, plane? That may not be every bodies flying mission, but from where I live, a lot of destinations go across a lot of water (UK, Scotland, al the Scandinavian countries, Channel islands, Mediterranean, etc.). I have no idea how much ?electrons? are consumed by the two Electronic Ignitions?? But if the alternator quits and you know there is no way to land for the next couple of hours, your heartbeat is bound to go up! I guess you could switch one ignition off, to save battery power? (you obviously switched off all other stuff and are now flying on your Whiskey compass), but still, how long will the battery last? Did you notice the problem on time? Or has the battery already been drained 50% before you figure out what the problem is? Hey,?. the battery may already be down to 50% due to ?old age?.

Regards, PilotTonny

You bring up many valid points. Old batteries, failing to notice the failure immediately etc. If you are flying over water with an electrically dependent airplane two alternators and two batteries will go far in keeping you dry. Alternately, consider one mag and a carb!

My RV10 has two alternators and two batteries. A bit more weight but hopefully I'll be able to complete all the missions as far as electricity goes.

 

[rracer10]

If I am IFR and my batt goes bad, I would wish to have a second battery.

If I am IFR and my alt goes bad, I would wish to have a second battery.

I have a second battery that I can switch onto the buss anytime I want. I can also switch off the primary battery anytime I want. I can also charge both of them at the same time or have them on the buss at the same time.

In planes of this size I don't believe 24vdc systems are any better than 12 volt systems, in fact they are more of a pain in the *** when you need to jump it to get it started....

What Greg says (see my previous post), is that if you have a 24 volt system you don't need a backup battery because you have more that twice the reserve. If you go with a 12 volt system, then you do need a second backup battery. This type of setup would work fine in an RV type airframe. Quote: "The bottom line is the HIGHER THE SUPPLY VOLTAGE, the better off we?re going to be up to a point where it starts to get dangerous."

So basically, a 24 volt system is much better than a 12 volt system in aircraft. The margins of reserve energy are much higher. You only need 1 alternator + 1 battery + 2 busses. Much lighter, more efficient, and SAFER in the long run.

 

[w1curtis]

What Greg says (see my previous post), is that if you have a 24 volt system you don't need a backup battery because you have more that twice the reserve. If you go with a 12 volt system, then you do need a second backup battery. This type of setup would work fine in an RV type airframe. Quote: "The bottom line is the HIGHER THE SUPPLY VOLTAGE, the better off we?re going to be up to a point where it starts to get dangerous."

Voltage is just motive force. It means nothing if there is no current for it to move. In a 12 volt system you get to about 10 volts before the **** hits the fan. In a 24 volt system you may be at 18 volts but if there are no amps to push, you are still SOL. The misconception here is that voltage will also drop to 10 before the system dies--not so.

So basically, a 24 volt system is much better than a 12 volt system in aircraft. The margins of reserve energy are much higher. You only need 1 alternator + 1 battery + 2 busses. Much lighter, more efficient, and SAFER in the long run.

Lighter? No not in our sized planes when you consider the required ancillaries.
More efficient? Maybe if you need to generate a LOT of power-more power than we need in our sized planes.
SAFER? Don't see how.

A 24 volt battery is two 12 volt batteries wired in series so yeah, you already have dual batteries. If you have to run hundreds of miles of wire, then yes, the smaller wire that is required in a 24 volt system would add up. Even in the biggest 4 place GA aircraft the weight savings from the wire is easily overridden by the bigger battery and the gadgets needed so you can still run your 12 volt devices. But then you are still hampered by the much more expensive 24 volt accessories (alternator, lighting, servos, etc). Two 12 volt batteries wired in parallel gives you the same reserves as two wired in series (24 volt).

I have a 1975 C177RG with a 12 volt system and my buddy has a 1978 C177RG with a 24 volt system. Every time he has to find an accessory, he nearly pulls his hair out. Light bulbs, starters, alternators, batteries are always a challenge to buy are and are ALWAYS more expensive than my equivalent. Then he has to carry a 3 pound 24 to 12 volt converter so that he can use 12 volt device via the cigarette lighter.

He just bought a new battery for his aircraft; 27 pounds @ $265, mine was 21 pounds @ $126. The benefit he gets for his 24 volt system; --his gear goes up twice as fast as mine. He wishes he had a 12 volt system.

 

[Sticky1]

Voltage is just motive force. It means nothing if there is no current for it to move. In a 12 volt system you get to about 10 volts before the **** hits the fan. In a 24 volt system you may be at 18 volts but if there are no amps to push, you are still SOL. The misconception here is that voltage will also drop to 10 before the system dies--not so.

Lighter? No not in our sized planes when you consider the required ancillaries.
More efficient? Maybe if you need to generate a LOT of power-more power than we need in our sized planes.
SAFER? Don't see how.

A 24 volt battery is two 12 volt batteries wired in series so yeah, you already have dual batteries. If you have to run hundreds of miles of wire, then yes, the smaller wire that is required in a 24 volt system would add up. Even in the biggest 4 place GA aircraft the weight savings from the wire is easily overridden by the bigger battery and the gadgets needed so you can still run your 12 volt devices. But then you are still hampered by the much more expensive 24 volt accessories (alternator, lighting, servos, etc). Two 12 volt batteries wired in parallel gives you the same reserves as two wired in series (24 volt).

I have a 1975 C177RG with a 12 volt system and my buddy has a 1978 C177RG with a 24 volt system. Every time he has to find an accessory, he nearly pulls his hair out. Light bulbs, starters, alternators, batteries are always a challenge to buy are and are ALWAYS more expensive than my equivalent. Then he has to carry a 3 pound 24 to 12 volt converter so that he can use 12 volt device via the cigarette lighter.

He just bought a new battery for his aircraft; 27 pounds @ $265, mine was 21 pounds @ $126. The benefit he gets for his 24 volt system; --his gear goes up twice as fast as mine. He wishes he had a 12 volt system.

I rest my case...........

 

[Sticky1]

things

* Amps Push Volts Thru Ohms

* Hometrons blow fuses

 

[rracer10]

Thanks for the post William. Electrical is not my forte. Since I haven't started my build, I'm in the research phase and Greg's article seemed to make sense. But there's nothing that can replace practical experience! Very good points you make.