In a deep cycle application such as providing backup power to systems after a charging system failure, A good LiFePO4 battery will provide much longer service at a steady voltage than any lead-acid chemistry and at about of the 50% weight per AH and for about quadruple the discharge cycles. There is a YouTube channel run by a guy named Will Prowse who does some great testing on batteries including testing them and tearing them apart to see what actual BMS the manufacturer is using. These batteries have taken over in a big way in the off-grid world for solar systems, yachts, and remote data stations and are very safe. They have very low risk of thermal runaway and have great steady voltage down to about 10% state-of-charge whereas an AGM or wet cell lead acid will drop to 10.5V at about 50% SOC. They also have significantly greater charge efficiency and basically no absorption stage so they essentially bulk charge until float voltage. This is great and superior to lead-acid batteries in all respects except three:
1. BMS is there to protect the cells and will disconnect charging, output, or both if parameters are exceeded. For airplane use one should ONLY use a battery with a quality BMS which does not disconnect discharge except in the case of a dead short which should be protected by a battery fuse, fusible link, or breaker anyway. EarthX airplane batteries are designed this way. Amazon Chinese possibly not so much. 2. The low resistance of the cells does not give the battery the simple self-regulation of charge current that at lead-acid does (resistance increases with SOC) so it can and will take all the currrent a charging unit can give at greater efficiency resulting in a faster charge rate than lead-acid. This is great if using a unit like the John Deere PMA on the Corvair conversion which always outputs max power full-time and the external regulator shunts the extra as heat. However a conventional automotive type alternator can be easily driven to the point it melts down and fails unless externally regulated to a profile that keeps the alternator temp in limits and provides proper voltage to the battery 14.4 charge, 13.1-13.3 float. 3. LiFePO4 cells can be damaged by charging at temps below 25F, so many BMSs disconnect charging if the battery is colder than that. Discharge is fine, but you can’t replace what you use until the battery warms up. On Fri, Jun 14, 2024 at 8:30 AM Matt Naiva via KRnet <krnet@list.krnet.org> wrote: > Jeff thank you this has long been my position. The steady state delivery > after a dynamo goes down also biases me to SLA... > https://youtu.be/FPBaAil4dNg?feature=shared > > > On Thu, Jun 13, 2024, 4:53 PM Jeff York via KRnet <krnet@list.krnet.org> > wrote: > >> I spent years as an engineer in Industrial Lithium Ion technology. Mostly >> BMS like Lithium system charging design and such. I actually even own an EV >> and its really cool but its just not prime time and I never see it go >> there. >> >> As loud as I can type it, I would never ever fly using a LIthium Ion >> battery as an engine starting battery and I would only fly behind AGM. The >> very thing that makes Lithium Ion so called great for propulsion batteries >> is the same thing that makes them extremely dangerous. That benefit is low >> resistance. Let me explain. >> >> In an AGM or any wet cell battery, when it goes bad it in 99.9999 % of >> the time it creates an open within its cell banks. So, instead of having 12 >> VDC you have 10 VDC or 8 VDC or 6 VDC. All fine. >> >> In a LIthium Ion cell that great low resistance will end up as a dead >> short within the cell array. Now typically what will happen first is >> probably what you are experiencing. The dead short is causing a logic >> voltage ( VCC or TTL) where your logic voltage is typically 5 VDC which is >> a portion of the 12 VDC of the battery by way of a voltage regulator >> circuit of 12 VDC. Since a Lithium Ion battery has such a low resistance, >> the effect will cause the 5 VDC VCC to vary to say 3.5 VDC. This will >> cause very strange effects in the logic circuits and you end up with very >> strange things happening. >> >> Now, the worst thing that happens is if you get enough Lithium Ion cells >> that go bad and short to ground, you get heat and a fire. This is why >> Chevrolet recalled all of its Bolt EV's and why when I was working the >> industry I saw so many odd things happen with the logic of a system or so >> many fried BMS 's or DC power systems. >> >> Don't get me started on the myth that there is so much new tech in >> Lithium Ion. Bunk...it's the same as it was 40 years ago. The changes are >> in the BMS systems. The pipe dream magic LIthium cells are far too >> expensive to produce at a cost effective means. >> >> The battery in my EV had to be replaced at a cost of $ 32,000. Thankfully >> it was under warranty. Its not under warranty anymore. Would you like to >> buy a very well cared for EV? >> >> W. Jeff York >> >> >> On Wed, Jun 12, 2024 at 9:13 AM mark jones via KRnet < >> krnet@list.krnet.org> wrote: >> >>> Yesterday I was doing a taxi test and had the following happen more than >>> once. This scares me enough that I am now very hesitant to use a Lipo with >>> BMS. >>> After about five minutes of taxi, my engine shut off as if the ignition >>> switch had been shut off. There was absolutely no power at the ignition >>> switch. The BMS took over and shut the system down. After about 10 minutes, >>> The battery came back to life and she started right up. Only to again shut >>> down after a few minutes of running. Why is this happening? Is it due to >>> the Dynamo? Why wouldn't my engine keep running just off the Dynamo. Does >>> the BMS somehow disable the entire system? I am feeling like Larry Flesner >>> said. I think I too will only fly with AGM batteries. Seems this BMS in >>> Lipo batteries is a source of failure we do not need. >>> >>> Mark Jones (N771MJ) >>> Oldsmar, FL >>> >>> flyk...@gmail.com >>> www.flykr2s.com >>> -- >>> KRnet mailing list >>> KRnet@list.krnet.org >>> https://list.krnet.org/mailman/listinfo/krnet >>> >> -- >> KRnet mailing list >> KRnet@list.krnet.org >> https://list.krnet.org/mailman/listinfo/krnet >> > -- > KRnet mailing list > KRnet@list.krnet.org > https://list.krnet.org/mailman/listinfo/krnet >
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