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Is this battery overkill?

SinCityJets

SinCityJets

Active Member
On my post “Is electronic fuel injection “there,” the one point that stands out is the redundant need for electrons.

With that in mind, would this be too much?

Earth X for the engine electronics, with a back-up battery (maybe a smaller Earth X, I’m not really sure why you would run a TCW over another Earth X)

And then another Earth X and back-up battery for all other components. Basically you would carve out all of the engine electronics and it would have its own Main Engine Bus.

With the Earth X batteries being so much lighter, I don’t think you are really adding dead weight here??

Two separate systems, fed by a main and back-up alternator.

Appreciate your thoughts and input. Also appreciate your thoughts on why you would use a TCW over just another battery.

Chad
 
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There is a pretty sound argument for using a different brand of backup for an EFIS or other critical system. For the same reasons, I'd think about different battery chemistry for the backup if you use LiFePO for the primary. Maybe (for example) a big EarthX for the main battery, and a smaller Odyssey for the backup. It might help to reduce the chance that a particular failure mode would affect both systems at the same time.

Lithium batteries could be more prone to failures than SLA, or maybe less. Doesn't matter as much as the fact that their failure rates and modes would be different.
 
So Brett, you would have to flip a switch to activate this battery? Would the engine have already shut down by this point? Would this be an in-air re-start?

Chad
 
SinCityJets said:
So Brett, you would have to flip a switch to activate this battery? Would the engine have already shut down by this point? Would this be an in-air re-start?

Chad
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This is a HD high quality 40 amp switch that connects this backup battery to the two isolated fuse bus feeds, each one has its own ECM, coil, fuel pump, and also ties into the avionics fuse bus that has its own switch if I need to load shed. The plan in case of alt failure.... is to run on the main battery, 900 Earth X for 30 minutes, (if I haven't landed yet) then back up battery on, field off, master off, start timer, every aircraft is wired different, so this is only how I am doing it, not saying it is the best solution but it works with redundancy for my setup. :rolleyes:
 
bret said:
The plan in case of alt failure.... is to run on the main battery, 900 Earth X for 30 minutes, (if I haven't landed yet) then back up battery on, field off, master off, start timer, every aircraft is wired different, so this is only how I am doing it, not saying it is the best solution but it works with redundancy for my setup. :rolleyes:
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I suggest that if your alternator fails, load shed right away including the master relay as this hog of electrons is not a good use of the remaining power.

The battery is only a "reservoir" of unknown quantity of useable electrons. A better plan would be to have a small backup alternator to help keep that reservoir full, and an easy load shed plan (checklist) should the main alternator fail. The backup alternator can produce a lot of power given a bunch of time, or it can just make what you need up to it's maximum capacity.

Bevan
 
My aircraft is electrically dependent both for nav and for power. What I did was a 60-amp primary alternator and a 20-amp standby alternator, and a single battery. The 20-amp backup alternator will easily supply all flight loads with external lighting OFF, so I have two valid independent sources of power. The battery recently got changed from a PC680 to an EarthX 900-VNT for a couple reasons, I wanted better cranking voltage in a partial discharge situation but I also wanted a better reserve of power in the far-fetched scenario of both alternators going offline. My nav (Dynon) has its own backup battery that's good for 45 minutes nominally (maybe more) and in the event of a dual alternator failure I can dump all my panel power and use the ships battery to power my fuel pumps only - that gives me 2 hours of fuel pressure under a new, fully charged battery scenario. I have one EI and one mag, so I still have spark without power.

The only reason I even went this far with the redundancy (how likely are you to lose both alternators in a single flight?) was because of my intention for long over-water legs with limited options.
 
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airguy said:
My aircraft is electrically dependent both for nav and for power. What I did was a 60-amp primary alternator and a 20-amp standby alternator, and a single battery. The 20-amp backup alternator will easily supply all flight loads with external lighting OFF, so I have two valid independent sources of power. The battery recently got changed from a PC680 to an EarthX 900-VNT for a couple reasons, I wanted better cranking voltage in a partial discharge situation but I also wanted a better reserve of power in the far-fetched scenario of both alternators going offline. My nav (Dynon) has its own backup battery that's good for 45 minutes nominally (maybe more) and in the event of a dual alternator failure I can dump all my panel power and use the ships battery to power my fuel pumps only - that gives me 2 hours of fuel pressure under a new, fully charged battery scenario. I have one EI and one mag, so I still have spark without power.

The only reason I even went this far with the redundancy (how likely are you to lose both alternators in a single flight?) was because of my intention for long over-water legs with limited options.
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I just need to point out that for an electric power dependent airplane like yours, having two alternators mitigates the loss of alternator casualty, nothing else. There have been incidents of twin engine planes (two alternators) losing all electrical power from a single buss fault. It is essentially impossible to avoid such single point failure risks on any single battery design.

As I have posted before, I offer that for electrical dependent aircraft (IFR and/or engine), a thoughtful two battery power distribution design mitigates more casualty scenarios that a single battery, two alternator scheme. I would always choose two batteries and single alternator over single battery, two alternator designs. Considering such designs eliminate the need for panel or engine backup batteries, weight is a wash.

PM me your email address if interested on how I do this.
Carl
 
Carl Froehlich said:
I just need to point out that for an electric power dependent airplane like yours, having two alternators mitigates the loss of alternator casualty, nothing else. There have been incidents of twin engine planes (two alternators) losing all electrical power from a single buss fault. It is essentially impossible to avoid such single point failure risks on any single battery design.

As I have posted before, I offer that for electrical dependent aircraft (IFR and/or engine), a thoughtful two battery power distribution design mitigates more casualty scenarios that a single battery, two alternator scheme. I would always choose two batteries and single alternator over single battery, two alternator designs. Considering such designs eliminate the need for panel or engine backup batteries, weight is a wash.

PM me your email address if interested on how I do this.
Carl
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I have had multiple alternators fail in my lifetime, but I've never had a battery fail catastrophically during use. I've had them go dead and not crank when I wanted them to, sure, that's happened to us all - but I've never had one die during usage. I choose to use the evidence of MTBF in my design, your mileage may vary.

And as you pointed out, there is no way to make a completely failure proof aircraft. Even a modern jetliner can be taken out by a single cause. https://en.wikipedia.org/wiki/Gimli_Glider As long as we are flying single-engine aircraft we are susceptible to single-point failure.
 
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airguy said:
. . .And as you pointed out, there is no way to make a completely failure proof aircraft. Even a modern jetliner can be taken out by a single cause. https://en.wikipedia.org/wiki/Gimli_Glider As long as we are flying single-engine aircraft we are susceptible to single-point failure.
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I might add to this thought -- Even a multi-engine aircraft is still susceptible to a potential single-point failure. As long as humans are included as part of the process of aircraft flight there is the potential for a human as the point of failure! Even having multiple humans involved in the aircraft processes is no guarantee of elimination of such failure points.

https://www.bing.com/search?q=Air+france+flight+447&qs=n&form=QBRE&sp=-1&ghc=1&pq=air+france+flight+447&sc=9-21&sk=&cvid=BD579FCFE0BE4FAF931D45935BD5BBA4
 
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