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CAUTION! LiFePO4 Battery Capacity!
I've had a couple of different topics recently on the Aerovoltz/Ballistic LiFePO4 batteries and also on alternator wiring connectors overheating. I just got some information from EarthX that is very interesting.
What I've found out is this: While the 12-cell Aerovoltz/Ballistic (same battery - different brand names) is easily capable of starting my Jabiru 3300, it only has a capacity of maybe 3 amps. Therefore, the battery gets pulled down quickly by the starter, and the Jabiru does not produce charging current until it hits 1900 rpm. That means all the electrical systems during taxi, run-up, etc. are running on battery only. (The Jab has dual magnetos so it doesn't depend on the battery once started.) During take-off and revving the engine beyond 1900 rpm, there is a sudden in-rush of alternator current to replenish the battery. Lithium batteries naturally have low internal resistance and allow the in-rush of current. I've been told the "20 amp" alternator might actually be putting out as much as 32 amps!
Technical support at EarthX said my 12-cell Ballistic was seriously under-sized in terms of capacity. He said my previous Odyssey PC680 had about 12.8 amps capacity. An EarthX ETX36D has 12 amps of capacity and was what he recommended. It's roughly the same size as the PC680, so it'll fit my battery box, and only weighs 3.5 lbs - 1 lb more than the 12-cell Ballistic. He assured me this would work well in my application and eliminate the in-rush of current from the alternator.
An added plus is that the EarthX has an on-board battery management system to balance charge the cells, prevent over and under charge, and protect the battery from excessive charging current.
So ... lesson learned - consider the capacity of the battery when choosing one for your application!
BTW, EarthX has great customer service and technical support - they quickly got me information I needed!
(Looks like the Ballistic moves to my '84 Honda Nighthawk!)
John
N750A
Replies to This Discussion
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Permalink Reply by Ken Ryan on
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I was ready to write off EarthX as shameless huxters, but their response (that their batteries are very close in weight to other LiFe batteries) is a good one and puts me at ease. I do like the IDEA of the onboard battery management system. If it works as advertised (and doesn't lead to other unintended consequences) it seems like a good way to go as it provides for extra protection.
The way I see it, the real problem was not the capacity of the first battery, but the inferior quality of the connectors. In other words, I think you could put that other lithium battery back in (now that you have replaced the connectors and the breaker) and not have any problems, despite the battery's lower capacity.
Thanks John.
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Permalink Reply by John Austin on
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No, I don't think one can say there would be "no problems" with the smaller lithium battery. This is due to the Jab 3300's alternator - it doesn't charge until 1900 rpm or above. "Any" battery will start it (and it'll continue to run on the mags), but a smaller/lower capacity battery is pulled down some by cranking, and then it has to power everything on the panel until 1900 rpm is achieved. With the smaller Aerovoltz/Ballistic, I would occasionally get a low voltage warning during taxi and run-up, especially in the winter when it takes longer to warm up the engine. I could envision a scenario of cold weather, difficult start/lots of cranking, prolonged run-up and then having to shut down for some unforeseen reason and "maybe" not having the reserve to crank again. So far with the ETX36D, the worst I've seen is 0.1 or 0.2 volts drop with everything turned on until I take off and hit 1900 rpm - more peace-of-mind that there is a lot more useful battery there!
By the way, Kathy from EarthX clarified her error in another email:
I stand corrected and it was my mistake for not completing the sentence correctly and accurately. I do apologize! I said. “For example , the Aerovoltz has MAYBE 3 amps of capacity where as your PC680 has 12.8 and our ETX36 has 12 amps.”
What I should have said was each cell has 2.5ah of capacity and there is a total of 12 cells. 4 cells have to be in series in order to get the correct voltage and then you have 3 in parallel to get the capacity. Therefore, the 2.5ah cells X 3 =7.5ah of capacity. (I rounded slightly up as there is a possibility they use the 2.6ah cells but testing doesn’t confirm this so that would be 2.6ah x 3 = 7.8ah.)
There are 2 factors you should use to match up a battery for comparison, the CCA and the capacity. I also noticed I said the ETX12 series is comparable to the 12 cell.
Aerovoltz CCA claims 410 but will test at 120CCA. Capacity is 7.5 to 7.8ah.
ETX12 CCA is 135 and capacity of 4ah.
ETX18 CCA is 230 and capacity of 6ah.
ETX24 CCA is 270 and capacity of 8ah.
ETX36 CCA is 405 and capacity of 12ah.
In the airplane world, I think more is better. None of our batteries are an exact match up, with the ETX12 series you gain cranking amps but lose capacity.
In the ETX18 series, you gain lots of cranking amps, and lose a little capacity.
In the ETX24 series, you gain cranking and capacity. This is the winner in my book for a replacement.
In the ETX36 series, you gain much more cranking and capacity all around.
But this is comparing it to the Aerovoltz and not the recommended battery of the PC680 for your plane. That is closest to the ETX36 series.
Sorry for my mistake….not an engineer and I remembered the 2.5ah cells but forgot they were in parallel. L I hope you can forgive my error.
Sincerely,
Kathy Nicoson
EarthX Lithium Batteries
John
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So EarthX says, "Aerovoltz CCA claims 410 but will test at 120 CCA." That is quite an indictment of Aerovoltz, basically calling them great big liars. I have to ask, from whence cometh the data?
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Well, I tried contacting Aerovoltz to give them a chance to respond. I was unable to get any response at all. On the other hand, I had additional questions for EarthX and my questions were answered quickly and thoroughly.
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Permalink Reply by David J. Beaulieu on
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So Ken...what battery have you decided on?
Dave
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Update: I finally got a response from Aerovoltz:
Ken, sorry for the delay, my website and servers were hacked and I had to change companies as it kept happening. So we are finally back on line and running.
I will never throw my competition under the bus or make up data while I am at. Our cranking power is a burst measurement that is taken during peak draw on our test engine. Our amp hour ratings are based on a 10 amp hour draw and are very accurate as we have many racers and vehicles in various forms of movement that run without a charging system so that amp hour rating is very critical to them and we have tested and tested for the last seven years in the motorsports industry under extreme conditions.
Testing batteries is like testing an engine on a dyno, you can get them to read just about anything you want with some input. I can tell you that we have several companies that are using our products as the OEM in their aircraft with great success.
Pipistrel, Kitfox, Just Aircraft, Back Country Supercubs, are some of the OEM customers in addition to all the aerobatic and racing pilots that we work with around the world.
You can watch our AV016 battery starting the EAA’s Zenith CH750 project on the EAA blog site and also on our Facebook that has a host of start video’s and flying to validate our success in the market.
We are into aviation, we live it and breath it. I am an EAA member, AOPA member, and local chapter 1114 member here in NC so we here for GA and its wellbeing, not just looking to tap another market with our product and bashing our competitors while we are at it.
Please let me know what engine you are looking to start with a battery and I can make a recommendation for you. Here is a great unbiased article that was in Kitplanes that gives you all the raw data you can ask for.
Fly safe and I hope we can help you in the future.
Kind regards
Steve Johnson
Everything Aero LLC
Aerovoltz
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kitplanes-article.pdf, 963 KB
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Hi Thomas,
I've had zero issues with the ETX36D. I doubt yours will need charging before the first start - as I recall, they are shipped fully charged and lose very little charge sitting on the shelf. Of course, I installed and used mine right away, but I would think even after 6 months to a year it would easily crank your engine ... and there is no downside as there is no "memory effect" such as NiCad batteries have.
While it is true that you need a 14+v charging voltage to fully charge a LiFePO4 battery and conventional "smart" chargers won't work (they are set up for conventional batteries and will quit charging before 14v or read the battery as "dead" and refuse to charge it), I wouldn't purchase a special charger - your charging system on the airplane will take care of that. If you accidentally deplete the battery, the onboard BMS will turn the battery "off" to prevent permanently damaging the battery. To "wake up" the battery, you simply apply +12V from a conventional battery with jumpers or a "dumb" constant-voltage charger, start your engine, and you're good to go.
BTW, EarthX sells a "jump pak" which only weighs about 1 lb so is practical to carry on flights. It has a short jumper cable and a USB outlet for charging cell phones and laptops and an integral LED flashlight. As opposed to some similar jump paks, this one uses the safer LiFePO4 cells rather than lithium cobalt (think Boeing battery fire!). One would need to have direct cables to the battery accessible without removing the cowl if one wanted to jump the plane safely. I bought one from them on an AirVenture special primarily for my car, but I may fix the cables and carry it in the plane, too.
John
(not affiliated with EarthX)
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I played "musical batteries" with all of mine. Originally had an Odyssey PC680 in the 750 and tried the 12-cell Aerovoltz/Ballistic for useful load increase (nothing wrong with the Ballistic, just too small!) Then, replaced the Ballistic with the ETX36D. So, the sealed PC680 went into my restored '82 Porsche 911SC (the only corrosion that had ever been found and repaired on the car was from the lead acid battery!) and the Ballistic went into my restored '84 Honda Nighthawk bike. So far, all three vehicles are very happy! :>)
John
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Anybody interested in building their own lithium battery (complete with BMS)? Here's how:
http://www.ebikeschool.com/how-to-build-a-diy-electric-bicycle-lith...
Keep in mind, this is not a starting battery, so some design modifications might be necessary.
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Permalink Reply by Joe Spencer on
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wow!
I installed an Earthx this afternoon. rolled it out and started it up...thought it was gonna spin outa the mount. impressive.
I've been at it a while and I've never seen a battery spin a starter like that. I've had a lotta kickback problems...I don't see that happening anymore unless it shears the starter shaft or something. I don't think it'll over power the battery thats for sure.
got 16# of old batt and wires etc out from behind the seat. put 4# of batt and wires in front of the copilot rudder pedals on the floor. Now It's nose heavy...but I got a plan. Will send some pics
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