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  #1  
Old 04-04-2018, 08:55 PM
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majuro15 majuro15 is offline
 
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Default Battery Failure - What happens?

With a lot of discussion about electrical system design, one of my big unanswered questions is what happens when a battery fails?

Now, I know you may get nothing, smoke, maybe flames, etc. with the battery itself, but what exactly does it do to the electrical system?

Without trying to dive down too many rabbit holes (let's keep it high level and generic), does an electrically dependent aircraft need a battery once the engine is running? Will the alternator(s) continue to power the system and will electronics still work? Or is that battery required as a capacitor / buffer?

Follow on question, what kind of actual battery failures have folks experienced? Massive explosion, meltdown aka Boeing 787, smoke / flames, reduced or zero voltage?

Thanks!
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  #2  
Old 04-05-2018, 12:49 AM
crabandy crabandy is offline
 
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Try it out, next oil change during the leak check/engine run unhook the - battery terminal and see what happens. It was/is very spooky for me working near the spinning prop, but a couple practice “non-live” runs maneuvering to and around the engine and prop help with my safety and comfort.
I’m EFIS only and dual electronic ignitions/alternators so I wanted to know what happens if the battery goes offline. Not sure how to test the smoking battery part though!
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  #3  
Old 04-05-2018, 06:08 AM
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rleffler rleffler is online now
 
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Quote:
Originally Posted by majuro15 View Post
With a lot of discussion about electrical system design, one of my big unanswered questions is what happens when a battery fails?

Now, I know you may get nothing, smoke, maybe flames, etc. with the battery itself, but what exactly does it do to the electrical system?

Without trying to dive down too many rabbit holes (let's keep it high level and generic), does an electrically dependent aircraft need a battery once the engine is running? Will the alternator(s) continue to power the system and will electronics still work? Or is that battery required as a capacitor / buffer?

Follow on question, what kind of actual battery failures have folks experienced? Massive explosion, meltdown aka Boeing 787, smoke / flames, reduced or zero voltage?

Thanks!
You'll need to ensure that you have a good battery to keep the alternator working by keeping the field energized.

I've got two PC680s in my RV-10, which has been flying for over five years. They are just starting to show their age and are slow to crank. I'm replacing both of them with EarthX batteries. Besides providing more capacity and cranking power, I lose 21lbs. This will help with aft cg issues.

I also have dual alternators to go with the dual batteries. I can isolate either battery from main bus or join them both in parallel. The ebus battery can be charged through a diode while it's isolated.
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  #4  
Old 04-05-2018, 06:16 AM
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A friend of mine had a master relay fail in flight. Fortunately he was not in IMC when it happened. In the process of diagnosing the problem he cycled the master, power didn't come back up. Alternate avionics bus feed switch to the rescue.

A few times over the years I've had car batteries fail dead short.
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  #5  
Old 04-05-2018, 06:42 AM
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dlloyd3 dlloyd3 is offline
 
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Too many variables for a simple answer.
Most battery failures due from abuse or old age at some point will not have enough energy to start an engine so the problem could be solved on the ground. Everyone that has a car, truck or airplane has experienced this, the most common failure.
A large radio shop put a 24 volt charger on my 12 volt Bo blowing the top off the battery, expanding the battery box like a beachball, bending the cowling door and latches. Doubt that could happen from power supplied by a runaway alternator even without a main breaker or overvoltage protection.
I have had an older battery fail open, something broke inside. Everything was powered from the alternator of a unknown period of time until the engine was shut down. Then nothing. 0 Volts. Borrowed a battery in Tuscaloosa.
Couple months back there was a lot of discussion here regarding lithium batteries shutting themselves down due to overvoltage and what would happen when the battery is effectively taken out of the circuit. Dan Horton did some testing. Search and read that.
I used to fly quite a bit on business, any weather flyable in a SE aircraft. Vacuum pumps failed 600 hours on the average. That was a concern. Alternators/regulators/wiring failed 600 hours on the average. That was an emergency. Airplane is going to the nearest suitable airport now. I changed batteries out every two years.
Now there is no vacuum pump, back up batteries on each EFIS electrical failure is less concern. The main battery will power radios gear for over 2 hours (tested). If my engine was electrically dependent however; that concern would ramp up quite a bit. Two alternators or two batteries would be part of the answer.
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  #6  
Old 04-05-2018, 08:57 AM
krw5927 krw5927 is offline
 
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In 2003 I had a 2-year-old lead-acid AC Delco car battery shed the positive terminal from the battery case. The entire terminal, including the attached wire to the car's electrical system, was just hanging free. Naturally, acid spilled all over the battery case and had run nearly everywhere in the engine compartment.

If you designed your electrical system similar to one of Nuckolls' diagrams, most likely your battery can be removed from the system by shutting off the master contactor, while your alternator is on the same side of the master contactor as all your avionics etc. Once during phase 1, I turned off the master contactor and e-bus relay in flight to see if the alternator would continue to power loads as they were switched on and off (I have magnetos and mechanical fuel pump so there was no risk of engine shut-down). Aside from some hum in the headset indicating less-than-ideal filtering of the rectified AC power, I found I could turn any loads on or off one by one and the alternator kept making power.

These results are only for my aircraft, as yours is likely designed differently. The point is, it's possible that things will continue to work. It's also possible that your alternator will quit all together. You only know by testing.
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Last edited by krw5927 : 04-05-2018 at 08:59 AM.
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  #7  
Old 04-05-2018, 09:16 AM
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Quote:
Originally Posted by krw5927 View Post
In 2003 I had a 2-year-old lead-acid AC Delco car battery shed the positive terminal from the battery case. The entire terminal, including the attached wire to the car's electrical system, was just hanging free. Naturally, acid spilled all over the battery case and had run nearly everywhere in the engine compartment.

If you designed your electrical system similar to one of Nuckolls' diagrams, most likely your battery can be removed from the system by shutting off the master contactor, while your alternator is on the same side of the master contactor as all your avionics etc. Once during phase 1, I turned off the master contactor and e-bus relay in flight to see if the alternator would continue to power loads as they were switched on and off (I have magnetos and mechanical fuel pump so there was no risk of engine shut-down). Aside from some hum in the headset indicating less-than-ideal filtering of the rectified AC power, I found I could turn any loads on or off one by one and the alternator kept making power.

These results are only for my aircraft, as yours is likely designed differently. The point is, it's possible that things will continue to work. It's also possible that your alternator will quit all together. You only know by testing.
I performed this test in my aircraft once purely by accident - bumped the master switch off during turbulence when I was reaching for my cowl flap switch. It took me about 20 seconds to realize what I had done and correct it, but for those 20 seconds the alternator handled the load just fine. No problem indication on any instrumentation and no voltage alarms from Dynon Skyview. I have not tested it further but it's not a bad idea...
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  #8  
Old 04-05-2018, 10:07 AM
rv7charlie rv7charlie is offline
 
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With the exception of Lithium technology batteries, your experiences with automotive batteries is the best way to evaluate how a/c batteries will fail. Anything is possible, and if you ask around long enough, you'll find an example (like that terminal falling off). But the overwhelming majority of failures are simple loss of capacity. (Capacity being the amount of energy the battery can store.)

If the plane isn't electrically dependent, capacity loss isn't a big deal and there may be significant loss by the time it won't start the engine. A battery can be down to 50-60% of its original capacity (or worse) and still start the engine reliably. It only takes a few percentage points of a battery's capacity to crank the engine.

It's apparently a little-understood fact that power and energy are not the same thing. A tank of gas is a lot of energy. A 500 HP car is a lot of power. A 500 HP car with a half pint of gas will accelerate very quickly for a very short time (and distance). A 50 Hp car with 20 gallons of gas will accelerate very slowly, but will go a looong way.

If the a/c is electrically dependent, you need to know the battery's capacity, because if the alternator fails, capacity vs load determines how long the a/c can stay 'awake'.

With even certified a/c becoming more electrically dependent, that's probably why the FAA added a requirement a few years ago to check battery capacity at each annual.
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  #9  
Old 04-05-2018, 02:08 PM
rapid_ascent rapid_ascent is offline
 
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I would suspect for a non Lithium battery the "failure" would be over an extended time period. Loss of capacity as others have mentioned being the main attribute. I doubt the voltage would suddenly drop but the charging current might go up as the alternator tries to maintain the battery.

For a Lithium battery its completely different since there are normally protection circuits that are included within the battery. Lithium batteries can be over discharged so they must cutout the load to protect the battery. Over charging meaning putting too much current into the battery may also be protected.
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  #10  
Old 04-05-2018, 03:06 PM
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majuro15 majuro15 is offline
 
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Thanks for the replies and information.

So looks like an electrical system will continue to function (assuming a functional alternator is part of the system) but of course is not ideal. Taking a battery out of the system could result in voltage spikes both up and down.

Good point on the alternator field wire being energized, otherwise the alternator won't generate any electricity and the system goes kaput.

Yes, lots of stories of failure modes out there. The terminal falling off is a surprising one!
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