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matronics(at)rtist.nl
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 Posted: Wed Jul 15, 2020 6:49 am Post subject: LiFePO4 friendly electrical system, was: Re: Premature Eart |
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Just as another data point. I run an AeroAkku LFP450D which I bought in Germany. It's in my Rans S-6S with a Jabiru 3300 engine. The AeroAkku replaced an Odyssey PC680 and with mounting hardware combined I shaved about 14lbs off the weight of the plane, which equates to 40 minutes of fuel capacity. The LFP450D has integrated balancer and protection circuitry, nothing external needed. It costs about 3x the PC680.
The charge circuit required no changes, the cheap Kubota regulator and the 25A PMA work just fine with this setup. I do keep a LiFePO4 specific charger on the battery when not flying, but other than that it's maintenance free and it spins my Jabiru like there's no tomorrow. Even when cold, after 'waking up' the chemistry by running a couple of loads.
I should really replace the battery due to age, I installed it in 2013.. After 7 years still going strong every time.
Rob
On 7/15/2020 4:00 PM, Charlie England wrote:
| Quote: |
On Tue, Jul 14, 2020 at 10:52 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | P.S.
> Such a system would not necessarily be unfriendly
> to SVLA.
I've got a new AeroVolts product on the test
bench right now running the traps on energy
vs. charge discharge profiles. I've got an
EarthX device waiting to run the same
tests. Already have lots of SLVA data.
I've been thinking a lot about the
LiFePO4 friendly electrical system
with a goal of reducing parts count
and cost-of-ownership. The weight
reduction may not produce observable
benefits but at least it shouldn't
cost so much or impact reliability.
Bob . . .
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Add my vote for an architecture that allows 'bare' LiFePO4 batteries to be used. While I have no desire to pay an almost 10X premium to save 10 lbs, I do think that the brand X crowd is deceiving themselves if they think the battery is a functional drop-in replacement for SLA. There are failure modes (and even 'normal' operating modes) that can take the battery off line, without any control by the operator (pilot). I suspect that many early adopters haven't done an adequate 'FMEA' on all the potential ramifications of inserting a fully automatic, non-user-controllable BMS in the loop.
Some things do benefit from automation, but others don't. For instance, most of us won't accept an engine controller that automatically shuts the engine down due to low oil pressure. We want to be notified, and make the call on shutdown based on immediate circumstances. Automatic dropping the battery off line could in some circumstances be just as hazardous.
Charlie
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matronics(at)rtist.nl
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| Posted: Sat Jul 18, 2020 6:43 am Post subject: LiFePO4 friendly electrical system, was: Re: Premature Eart |
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Hi Rob, | Quote: |
I'd never seen that brand before, so I looked them up.
https://www.aeroakku.com/LIGHT-SPORT-AIRCRAFT/-AEROAKKU-LiFePO4:::6_139.html?language=en&MODsid=3024acbfbb1e3575f16a62b009d3bb51
1st thing I noticed is that it costs 299 Euros, or $341 US dollars. I pay around $40 for the SLA batteries I use.
2nd thing I noticed is that it's a 7AH battery. No doubt it's fine for starting, but it's about 1/3 the energy capacity of the SLAs that I use. That means that if you're running electronic fuel injection, it'll be good for about 15 minutes after the alternator dies.
What I *didn't* see (at least on that website) was any info whatsoever on the BMS. Since that company also sells the more common brands of batteries, it leads me to believe that they are rebranding someone else's battery, but there's no documentation. Which brings me back to what I wrote, above. With the addition of, 'we don't know what we don't know'. 
Charlie
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Hi Charlie,
They are selling in Europe only, and have been doing so since 2012 or so. I think that's even earlier than EarthX? The AeroAkku brand is their own development, and they started selling a couple of other brands as well over time. The AeroAkku BMS is embedded in the battery, no external circuitry required. The Oddyssey it replaced costs about €100 over here, so 3x for LiFePO4 and 14lbs saved.
Indeed 7Ah doesn't sound like much, but it all depends on your power budget. On my Rans S-6S with Jabiru 3300 using a gravity-fed carburator, my power draw is very low. I just tested with everything I have switched on (Funkwerk radio + xpdr, Stratux receiver, AvMAP UltraEFIS, LED strobes (own design, modified Kunzlemans), LED landing light, an MGL FF-4 and an Insight G2 engine monitor. Also powering a Samsung tablet and a phone. All this draws just 5A steady.
I started with main bus measuring 13.1V. After 40 minutes at 12.8V and after 50 minutes this had dropped to 12.6V, everything still operating fine. It then took another 10 minutes to drop below 12V, after that things went pretty quick. But even after an hour I still had juice to operate my electric flaps. And this is on a battery that enters it's 8th year.
So for my mission, this battery is perfect. For yours not so much.
Rob
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