Busting the 20%-80% SOC myth for LiFePO4 batteries.
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- เผยแพร่เมื่อ 1 มิ.ย. 2022
- I'm reading many comments under my video where viewers state they only want to use their battery between 20-80% to prolong its life and reduce degradation. This widespread 'myth' may work well for Li-ion batteries but not for LiFePO4 cells. I explain and show you why it is (almost) impossible to use this SOC window with LFP batteries.
This is a bit of an introduction video about how far to charge and discharge LiFePO4. It is in preparation for a hole series of future videos about settings in solar charge controllers, inverters, BMSes and shunts.
As always, please leave your comments, explanations and additions below, so we can all learn and share our knowledge. Thank you if you have already.
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Because of your presentation style, my brain is absorbing the information without undue fracturing!
Thanks.
Looking forward to dive in to those settings. Your expertise make a lot of sense. Learning so much as always. Cheers my friend
Awesome analysis and comparison of the 2 chemistries Andy. Thanks for spending the time to bring a better understanding of the characteristic differences.
Thank you so much for your contributions, the timing could not have been better for me because I’m putting my 280ah system together now so I’m looking forward to your future videos .
Exactly the information I was looking for - that's kind a scary ;) Unravel all these weird hardware settings would be a real interesting project. Thank you Andy!
Merci pour tout ces judicieux conseils ANDY. Bonne continuation.👍
Another great video Andy.
Really looking forward to a more indepth look at the many unexplained parameters of bms's if that comes up as part if the new series.
Wow, l learned so darn much from this video. This was one of the most informative videos I have watched about charging LifePO4 batteries. And I watch a lot. THanks so much for your great videos. You have a fan and will continue watching.
I've seen li-ion based cells subdevided into 6 families. LiFePO4 is one of them, there are 3 types with mixes of Nickel, Manganese, Cobalt and Aluminium oxide s. These became popular for cars, power tools and 18650 cells. Most people think of these 3 types when mentioning li-ion. Would be better to refer to them as li-NMC , li-NCA to avoid confusion with LiFePO4.
Looking forward to this series.
Great stuff Andy, I look forward to the following experiments
Andy, thanks for this fantastic video. Incredibly well done.
Great topic, exactly what I need, can't wait to watch next episodes
Andy your research is so helpful
No matter how many times I watch your videos I always reference them time to time for help . Helped me get off the crooked grid People wish they could be as cool as us off-grid family ❕✌🏼
Thanks a ton buddy 👍🏼❗️❗️❗️🇺🇸🌞
You are an excellent scientist, and I very much appreciate your explanation of charge voltage at the atomic level!
Thanks. I really need this and the type of info that you plan on posting. I had thought that I would not use a smart shunt just to save money, but now, I see the need for one to monitor the state of charge. It is interesting that counting electrons in the form of coulombs is really the most important measure in relation to SOC. Will be looking forward to your next few videos.
Thanks Bill. You can us the 'smart shunt' of the BMS as well but, but, but... it's not as reliable as the real smart shunt.
Great video, and looking forward to your settings series.
Coming soon!
This is one of the most informative videos I've ever watched in regard to SOC on Li-Ion and LiFePO4 cells. Thank you!
Thanks a lot, glad it made sense and helped.
@@OffGridGarageAustralia look up carpen battery..70 yrs,,no charge..
@@OffGridGarageAustralia I been building off grid power systems for over ten years, I haven't ever kept up with lithium, I know lead acid, NiFe and nicad indepth, but I have a chance to win a 30kwh battery, and if I add 6 cells a 40kwh lithium battery for my self! This has helped a ton to get up to date, and an idea of what I need to design the build.
Going to be painful testing 24 individual cells! but worth it!, thanks to your videos I am selecting the JK BMS, I'll fabricate my own copper buss bars though!
@@Refertech101 Thanks for your feedback. All the best with your project. It will be great and very rewarding!
@@harrywalker968 da daaaa, vor sa distruga muzeul tehnic unde se afla...
Exactly the way I understood it after playing with LiFePo4 batteries for a few years. Most knowledgeable videos about these batteries.
12v LiFePo4 im using settings in my SCC LVD at 12.6v and charging voltage at 14.2v i like that setting compared to default (Li) 11.5v LVD and 14.4v charging using a SRNE 40A SCC.. your channel is very informative thank you
Verry clear explenation Andy, nice job as allways
Looking forward to see the results, i kind off winged it when i made my packs.
To make full use of the chargers capabilities i even went as far as to make 18S packs and charge them to 64V (max Victron voltage) this would be 3.55V per cell.
Dangerously close to 3.65 i guess but in a perfect world... i can never overcharge them.
In my installation you can clearly see that at 98%SOC the pack voltage is still only 60V (3.33V per cell) and after that it goes realy quickly, but to prevent cell runaway the batrium lowers the charging rate for the "top balalnce".
there are so many cool tools out there to manage your batteries, gonna be nice to see you play with them.
Batrium should send you a sample, they are "local" for you i guess...
Keep it up Andy, 40K subs soon!
Hi Andy, more great info as usual. As soon as the temperature in Melbourne rises over zero in Melbourne! I am going out to my van to reset my 200 amp LiFePO4 to use the full capacity (not just 80% to 20% ), THANK YOU!
Ok, secondly I am looking forward to the upcoming videos as mentioned, but one thing I would REALLY like you to explore/discuss is "Separate Port" BMS's.
There is a lot of poo pooing separate port BMS on the Net, this seems to stem from the lower charging rate available versus the output.
Now I agree that this can be a factor in a stationery system with lots of panels, which is why those systems should be a totally different discussion to RV systems.
Essentially you really do need a separate port BMS in an RV for obvious reasons, secondly the lower input is never likely to be an issue on an RV simply because you would be hard pushed to get enough solar on the roof to exceed the input valuation.
Personally I have a Daly 200 amp output by 50 amp input (dumb) BMS. I seems to be working fine for about two years, but I would really like to upgrade to a BMS that has Bluetooth and is fully configurable, but where to find such as beast?
I am aware that "hybrid" BMS's are apparently starting to appear, but I think it is still early has for them.
What I really want is something like the JK BMS with the internal balancing (nice), but with a separate charging port, any suggestions?
BTW, Daly has very bad communication skills, and don't make it clear you can order a BMS from them to order, that's how I got my 50 amp input model.
Also people should note, some distributors of Daly products (like Deligreen) are hopeless, they supplied me with an instruction set for connections for the BMS that was totally wrong and would have blow it up on connection.
P.S. They also lie through their teeth.
PPS,. currently everything is controlled by my Victron BMV712 networked to the Victron MPPT.
Great unboxing video!😀 Looking forward to the upcoming series on settings.
Coming soon!
One of your most valuable episode ever. Thank you so much for sharing your thoughts and knowledge. Very much appreciated! 🙏🙏
Thanks a lot for your ongoing support and donations, Lino.
@@OffGridGarageAustralia It’s the least I can do for you. Sometimes I am asking myself how much gear I would have destroyed (and money lost) if I would have generated all the knowledge you are sharing on my own. 😅
2nd time watched it . skipped all easy informations those years you gave and i still find new ones.... . thanks.
I never thought I’d tell a block I’m excited but hey there’s a first time for everything ! I’m excited to see your results and findings Andy Mate. Mate 👍
Great to got you excited, Paul Hardie 😃
There will be more for you soon here. And thank you for being here!
Extremely valid information Andy. So we can extend the life span of our, kind of expensive batteries! While utilizing as much of our investment as possible!
As always, Thank You!
Excellent and really knowledgeable video. Better than most others that really do not know much about lithium batteries.
Looking forward to this Andy.
Fantastic explanation Andy.
Thank you for the info and knowledge sharing! Keep it up!
Very interesting. I am looking for the next videos about this topic
another great video, very informative video with all of the key points I have been needing so far
Great, thank you!
Thanks as a lot of good information is always learned from your videos. Keep them coming!
Thanks, will do!
As usual a very interesting video, Andy. I am looking forward to all the settings. Still strubbling with my absorption and float specs from the Victron RS450(wich I set close together).
Hope to see/hear you soon.....
Very soon, Victor, it is pretty much in production...
Very interesting!
Great explanation.
This will be interesting. Looking forward to all the different opinions here and the facts as you present this.
Same, just started reading...
Can’t wait🧐 getting batteries sometime in June, so will be interested in the info. Love you too! (See I did watch to the end) 😊
This is my first experience with you, having only just found the solar garage. I’m extremely interested as I plan to be building an off grid system in the near future & things have changed drastically since I was last fully off the grid. Looking forward to more 👍
Thank you and welcome to the channel. It's all here...
@@OffGridGarageAustralia Wow, you truely are a nice man. Thankyou. Can’t wait until we build my new system……Victron all the way 👍
Love you and your work here
Wow and thank you. This has got me wondering now about a control use algorithm to compensate for the drifting of the SOC when controlling use based on Amp-Hour removed. I'm thinking about how alternating the control variable from voltage, to %, to amp-hours removed, and repeat, at a period that could be set or derived, could put into place an automatically compensating SOC
Oettinger! 😄👍🏻(I am wondering what it tells about me that this is the first topic I am commenting on on your channel, Andy. 🤣)
Seriously, I really enjoy the ride through your experiments and findings. Great stuff. Keep on going!
Thanks a lot for your first comment, Jürgen.
Perfect timing Andy, I'm finally setting up my own battery 2.0 and the Smart Shunt is part of that. So I'm keen for a deep dive into the settings.
Me too just in time. Perfect!
Next weekend i will install my first ☺️ 8x 280 with jk BMS and victron charger(800 watts panels)
@@camielkotte this is my exact setup. I have 2 pcs of 435w panels and 8pcs of 3.2v 280Ah Eve. I have a Victron MPPT 100/30 scc. Pls let me know how you go. I ask Andy whether the panels are enough to fill the battery for the day. I am planning to run fridge, freezer, washing machine and dryer for this setup.
@@noelbondad7423 hahaha. Funny. My pannels are 395. I have a 100-30 and a 75-15 SC. Panel lsc is 11. Thinking about a east-west setup and maybe more panels. But since we are only weekends and high summer at the cabin 2 panels should be enough. Only problem is a massive oak tree full of various kinds of birds right at the south ... So i oversized the battery.
What consumers i use will proof yhe choise of wh insyalled are enough. We want a microwave and a little oven for bread. Cant decide if it must be 24volt(thick cabling) or a 230volt (massive inverter).
The later Ovens use up to 3000watts during pre heat i believe where 24volts dont. Curious.
What kind is your sine inverter?
@@noelbondad7423 last weekend my brother helped install both pannels and i connected one. Today i replace the SC with the second panel inparalel. Must do some woodcrafting before placing the battery and tow the dead lead away.
Succes to you. Saw you channel, will look at it tonight.
@@camielkotte I have a 24v sine wave inverter of 2500 watts continuous and 5000 watts surge. At the moment my old setup is 24v system. 1 panel of 435w, Victron 100/30 Scc, 2pcs of 100Ah LIFEPO4 which I connected in series to make it to 24v. Now I want to UPGRADE my system with Eve 280Ah I mentioned above. I bought another 435w panel. These panels are Voc = 49.9volts. I am NOT SURE whether my Victron Scc can support it since its max is 100volt which is at the boundary of my 2 panels. Actually, my other issue is whether the 2pc- 435w panels can fill the battery for the day.
Your informations are really good, as I just got my new LiFePo4 Bat -Pack! It helps me a lot! I will make 16S4P 280Ah Eve-cells
Great video Andy, thanks very much. 🇬🇧
Thanks Andy
Great video. Very informative.
The danger with keeping a near100% full LiFePO4 on a float voltage is that the (poor quality) charger can have an AC ripple with short spikes above 4.2volt even though the DC voltmeter says it is at 3.6volt constant float. Multiply values depending on your battery; 4s, 8s or 16s.
Those voltage spikes can cause metalic lithium plating on the electrode, that is permanent damage.
I charge my battery untill the first cell reaches 3.65v and then stop for the first cycle of the day. BMS calibrates this event as 100%, after calibration charging is resumed at 92% and stopped at 95%.
At midnight the flag for "calibration done" is reset so that it will charge again to 3.65v to recalibrate the next day.
The article "Practical Characteristics of Lithium Iron Phosphate Battery Cells" at Nordkyn design discusses the memory effect of not charging the cells to full (3.65v) on a regular basis. It starts building up a hump on the curve which gradually shifts to lower SOC, this means charging to only to 3.4v may reduce the usable capacity over time bacause it reaches 3.4v at a lower SOC.
In a truly off grid setup the typical daily cycle would maybe be 70% to 100% (defined as 3.65v) . Where I live there are infrequent events of consecutive rainy days where SOC drops below 10%.
I found the article, was very interesting. Regarding memory effect: it seems to take a long time for this to occur, and is generally reversible. The author states in the comments: "Memory effects don’t become permanent, they just become more difficult to overcome. [...] Performing a full recharge once or twice a year would appear to be quite enough in most cases."
@@ed-ey1yb This is very interesting to know. I made a note beside my HWT - which I drain and flush twice a year, as a self reminder to ensure the same for the battery bank.
WOW cheap charlie chargers with ripple and spikes - may explain the quite common sort of fire from these e scooters left on over night charge
Outstanding discussion well backed up by theory and practice.
I just wish more folks subscribed to that formula for success.
Thanks a lot, appreciate you feedback!
Greetings from South Africa Andy. Cannot wait for this new series, Thank you!
Ps. Have you heard about cathodes being Yitterium dipped for preventing heat degredation?
Thanks Andy - hilarious beginning as usual.😁
Very good topic- BTW I’ve received both my JK BMSs from China, one for my van (12v) and one for home garage (48v) already.
I’m impressed with the speed of delivery, obviously air freight!
My 400Ah Winston LiFePO4 cells for our caravan are now 6.5 years old, and have been charged usually to 3.45 volts during daily use, and then maintenance charged during storage (we don’t usually use the van in Summer) with a small solar panel (just around 50w, and only late afternoon sun) to a lower state, typically only 3.3v just to avoid any chance of going too low. However I know from experience that :
1. The actual state of charge can be quite low, as the Victron shunt (Bmv 700) gets waaay out of calibration over time, ie: exactly as you said. The ONLY way to recalibrate it is to fully charge the battery. I’ve seen it say the battery is at 100% during storage periods when it’s actually at probably closer to about 35- 40%.
2. My degradation is still absolutely minimal. I have capacity tested them last Summer (Feb 2022) by running an aircon and found the capacity at something significantly over 380Ah- I wasn’t game to go any lower as I didn’t have a BMS on the van, (but will have one soon!) and this means I would have had to watch individual cell voltages personally, just not worth the hassle.
Cheers and thanks again.
Thanks for sharing, Dave.
Just be careful with charging the 12V batteries with such small voltage, it can overcharge them and you're reaching a high SOC at 3.3V already and the charge controller keeps charging. It might be better to charge them to ~60% and turn of all loads and the charger. With 3% self discharging there should be now need for a trickle charge for quite a few months.
The Winston cells seem to be far higher quality and also better matched.
I've got your email as wee and will reply soon. Cheers.
@@OffGridGarageAustralia Thanks again Andy.
I certainly hear and understand what you’re saying about the longish periods in storage with 3.3v, however should have added that I feel I’m very safe as I very regularly use light loads such as charging my garden tools from the van’s inverter, and often even other items as well such as lights and even sometimes aircon if I am doing things in the van. (I have a 2.5 kW Panasonic split system in the van.)
The maintenance solar panel only receives mid to late afternoon sun- net result being that my actual state of charge usually goes down hill over time even though the Victron usually says 90- 100%. (As you know, that % SOC figure is useless when the battery hasn’t been at top of charge for a sync for a long while.)
For example, the last time we pulled the van out of it’s carport into full sun for a charge before using, I needed 250Ah going in to the battery to hit the top of charge, so the real SOC was probably something like 35-40%.
Weather permitting, we hope to use the van perhaps from the end of this week. I’m guessing that I’ll need to pump something like another 200Ah or so in to fill the battery, wild (educated ??) guess. Cheers
Small correction: LiFePO4 is also a lithium-ion battery. They all are. It would be better to distinguish by chemistry: Lithium Iron vs Lithium Nickel/Cobalt batteries. LiFePO4 really doesn't mind being charged to 100%. Keeping them at higher voltage (3.65V per cell) is more problematic since you can actually overcharge. Similarly, keeping them at 0% (2.5V) is generally not good, but anything over 2.5V (say, 3V which is pretty much still 0% state of charge) is fine. In other words, stay away from the very extremes and you're fine.
Thank you!
my observation of multiple laptop battery packs and brands is that their 100% charge requires cells to be above 4.2V. This has lead to many packs failing with just one or two bad cells; suggesting to me that these cells were over stressed. I'm imagining that something similar might happen with LiFePO4 cells driven to 3.65 or higher.
@@zaneenaz4962 "In the old days" we also pushed LiFePO4 to 4V as well. I agree that even 3.65V is pushing it, especially since there isn't much energy between 3.5V and 3.6V in the first place - at least for solar. If you do fast charging at high C rates, the voltage will rise faster and you might need to go to 3.6V or something to get the most out of the cell.If you can absorb for longer periods of time, even 3.45V like what Andy does is enough.
@@upnorthandpersonal What's the real difference between absorption @ 3.45V for longer and float @ 3.375V until the sun goes down? For example, I absorb @ 3.5V for an hour and float @ 3.375V until the sun goes down (~6 hours this time of year). Would the batteries benefit from changing to a 4 hour absorption @ 3.45V and float for @ 3.375V for 3 hours? Or are we just splitting hairs at this point?
@@8b10b The key thing to know is that LiFePO4 wants to settle at a certain voltage, even after longer absorb stages. The important thing is to let it do so, which is why floating at high voltages is not a good idea, and 3.375 is often chosen below this settling value (in principle, you don't need float at all).
You can absorb for longer at 3.45 compared to 3.55 for example, but that's only valid if you have the time to let the battery absorb. If you want to charge faster because you don't have this luxury, you have to go to higher charge voltage.
In the end, for solar applications where we're talking low C rates and in principle can afford to charge slower, it doesn't matter. There is a lot of fine tuning one can do based on weather/seasons/etc. but one can easily go too far with this and spend way too much time tweaking parameters...
Thank for the eye opening information in this video. I was very interested in being shown the mechanism that causes degradation on charging. Does it work the same way on high discharge? I often see comments advising a max discharge of .2C for maximum battery life. Is that strictly true?
Hi Andy, new to your channel and building battery banks. I find your content so helpful to me as I'm learning, and how well you explain every little detail. I am in need of new cells, are you able to share the details of where you source your cells from.
Thank you for the detailed information you provide on your channel.
Regards Des
Hi Andy great video keep up the good work
Awesome explanation
I made a 100ah 12v lifepo4. I added cheap voltmeter-usb combo to the pack. Digital voltmeter reads 14.9v. I recently bought a smart sensor which reads 13.65v at rest. Been running battery for two seasons no snd.they are amazing.
Neat video Andy, One thing to highlight is that the EV world 20-80% rule is purely about reducing the time it takes to charge not just degradation risk.
Thank you Andy, just in time my first 16 280Ah cells arrived this week. 🙂
Hey great!
Nice work !
ANDY, everything you just said makes perfect sense. LIfPO's were designed to be fully charged and fully discharged for a certain number of times before degradation sets in. But we all hope in the long run a little less heat when charging will lengthen the serviceable life of the pack. So for me, ill keep it down to 3.55 volts max charge voltage per cell, with a 4 hour float at 3.45 volts. Beer is on me!
A 4 hour float could overcharge them. These are not car batteries. having your BMS get every cell to 3.45 and balance would be better. he showed us where the curves are for these cells. 3.5 could even work but would stress the battery a bit more.
Only when you need speed charging (boat, RV, less sun hours) it is necessary to go above 3.45. Ones mileage will vary indeed.
For stationary and fair sun hours there is less need for higher voltages when charging...
So Andy told...
Thanks a lot for the SPAT 🍺, Bruce. Lower your float a bit and I'm happy with your settings. Thanks again for your support!
Thanks Andy. Looking forward to the research study and testing. Have you or anyone found any real world research testing on the actual effects of over and under charging with LFP cells? I'll include references to some research papers, which suggest that it's thermal effects that largely contribute to substrate damage, and more a function of charging rate than absorption charge voltage, and that overcharge damage typically occurred at voltages above 3.6v. I could not find one study that suggested did several hundred charge cycles to 3.2v vs 3.6V that I seem to recall found no appreciable degradation until charged to over 4.2V to 4.8V. but if I do I'll add it to this post.
Here's some articles that are bit of a dive but give some insights into what is going on at the chemical level:
LFP overdischarge conflicting voltage limits - Thread starter Hans Kroeger Start date Jan 21, 2021
DIY Solar Power Forum - Nature Article number: 30248 (2016)
'The Degradation Behavior of LiFePO4/C Batteries during Long-Term Calendar Aging March 2021' -
Energies 2021, 14, 1732
"Because the 20% capacity fade and/or 100% internal resistance increase are considered
to be the EOL criterion which are widely accepted, almost all of the tests performed in
the aforementioned literature are carried out within this battery life span. There are few
studies on aging behavior outside this range. Thus, this paper conducted an accelerated
calendar aging test on a commercial lithium iron phosphate (LiFePO4) battery over at
least 27 months. By considering the storage temperature and SOC level as the stress
factors, an aging test matrix was designed such that the tested batteries were subjected to
the aging test under five different conditions. Based on the aging results, the impact of
storage temperature and SOC level on the long-term performance degradation behavior of
fifteen LiFePO4 battery cells was analyzed."
'Failure Investigation of LiFePO4Cells under Overcharge Conditions - 159(5):A678 - researchgate'
"The correlation of the changes of
cell skin temperature and voltage with cycle number suggest that an
internal shorting of the cell was developing with overcharging, which
eventually led to the failure. Taking a close look at the temperature
curve of each cycle (in the 10th cycle shown in Fig. 2c), the cell-skin
temperature slowly increased with time but began a sharp increase
at the end of the charge, indicating that the overcharge caused detri-
mental damage to the cell components. The same pattern repeated
with cycle number for each cycle, and the temperature continued to
increase until failure. The temperature increased with charging, then
reached the highest temperature at the end of the overcharge process
(33◦C at 5.28 V, peak 1), then decreased with discharging; however,
after the discharge plateau, the temperature increased again to another
peak at the end of the discharge (26◦C at 2.8 V peak 2). As for the tem-
perature at peak 1, the temperature increased with the cycle number at
a rate of 1.36◦C/cycle, reaching 45.8◦C when the battery failed. It was
also noted that in the last five cycles, the temperature increased with a
much higher rate, 2.54◦C/cycle than that of the first five cycles (only
0.02◦C/cycle). Compared with the temperature change at peak
Jack, did your text get cut off. Seems to end adruptly.
Danke für das sehr informative Video. Du inspirierst mich meine "Balkonanlage" umzubauen. Victron Laderegler ist schon hier, Hankzor JK ist bestellt.
Wenn die Akkupreise wieder gegen Normal gehen werden auch neue (280ah) Akkus bestellt.
WENN die Preise wieder runtergehen, kaufe ich gleich so viele, das die gleich wieder steigen. Darauf warten wohl viele. Die Nachfrage ist einfach viel zu gross...
Actually Andy, you are so spot on that I’ve got nothing else to say but…..thanks!
And... thank you, Karl!
very good, you got a new subscriber here in QLD 👍🏽
Hi from Sweden, I love your videos! 😀
the bench is clean and free - looks like new project on the horizon
but that was just at the beginning of the video before you unpacked that lot of stuff.
Ur the best for all of us newbyes in lithium battery world. Fantasik videos
Thank you very much!
Andy, please explain calendar aging? Thumbs up and still subscribed!
Another great vid, I have often had similar thoughts with all ur testing video experiments, (hours and hours of them), why push the curves? Look forward to ur new coulomb counting methods and trickery. Cheers
Yes, it is far easier to stay withing the knees and use the rising/falling voltage as a trigger to stop charging/discharging.
Spot on.
My car audio batteries get half-ish discharged and recharged several times a day. From 3.2 average to 3.6. The high amperage demand is what I think will kill them before anything else. When I enter in competitions the batteries get abused. My amp-clamp (dmm) has shown over 300 amps on one out of the four 1/0 cables feeding the amps. My home system goes from 2.85-3.48 and NEVER see over 120 amps. Itll outlast the car audio batteries BY FAAR. Excellent video Andy
Thanks for sharing. I always wondered why you guys don't use supercaps for this sort of usage. Or at least LTO cells...?
This video was very emotional for me, so many tears Andy. Do you think you'll make a video reviewing your settings in your Charge Controller and Inverter? Would love to see that.
The video is coming soon, stay tuned... wipe of your tears first!
Thanks!
Richtig gutes Zeug.
Reasons for the coulomb counting being off:
- It does not count balancing losses (minor)
- It does not count self discharge (minor)
- Most importantly: It integrates (adds up) systematic measurement errors (offset, gain, linearity) over long or even extremely long timespans. Even an offset of just 100mA can accumulate to big deviations when no recalibration is done regularly.
SoC estimators for NMC, NCA and LTO usually can use the OCV curve to recalibrate to when the cell is known to be outside of the nonlinear ranges at top and bottom. For LFP it is a different story: Your best point for calibration is when the cell starts to become nonlinear at the top end. This is easily recognisable for a BMS observing the rate of voltage change. This is also the reason why e.g. Tesla recommends charging to 100% when you have a MIC LFP model.
With respect to ageing: You said it at the end, high voltages themselves will also accelerate degeneration. This is due to high voltages providing activation energy for unwanted side reactions of active material and electrolyte.
The c-rate sensitivity also depends on the cell construction. For high power types, high c-rates are not that critical (except for the temperature raise they naturally entail). For high energy types, this congestion and cracking issue is much more relevant. The reaction speed (or for Li chemistries, the intercalation speed) is limited and pushing beyond it increases the energy available to deteriorating processes again (mech., chem.).
Also all of the shunts I've used don't detect less than 0.5a flowing, so small current draw such as your charge controller overnight, phone charging, or LED lights may not be counted.
@@BradCagle Yes, thats true. There are chips that do some fancy chopping to be offset-free, but if a more simple variant is used, manufacturers usually just suppress the noise and offset around 0 because that is so visible to the customer when he has nothing attached but there is still something bobbing around ;).
Great video again good insight into SOC. Have you looked at or tried a Batrium BMS its an Australian company and from my limited research they look great but the price tag is a little high but they do everything you need bar getting another beer from the fridge. Keep up the good work.
Thanks a lot Keith.
I'm in contact with Batrium but felt it's a bit too much. I rather wanted exploring 'normal' BMSes and their flaws, helping more people out and sharing my experience.
I'm sure the Batrium will just work fine without problems. But it's like making videos about Tesla's Supercharging: it just works and is boring to watch.
I appreciate the graphs showing the difference between Lion and LiPO4.
Unfortunately, my Bluetti solar generator was not charging its LiPO4 batteries properly. They overheated at 100%, because they bulk charged to almost 99%. Its 30C here, but no excuse to not being able to function properly when I have a BIG fan blowing on it!
I told customer service, but no one understood my technical question to update the firmware. I now know where their charge rate was improper. Returned my EB3A, since it could never achieve proper life expectancy!
Bulk charging to 99% is not a bad thing with LiFePO4 and usually works well. Once the voltage rises to over 3.45V, the cells are 99%+ charged anyway.
Morning Andy, I see you have nice weather up there today, no rain. I was thinking want you are saying, would voltage aka pressure be the problem in this case? Wouldn't the crystals form under pressure?
The flat charging/discharging curve of the LFP is addictive. Voltage sag was a mayor pain in the arsch with AGM, especially in freezing temps.
Voltagesag with AGMs suck but charging LFPs in freezing temps suck even more...
@@windsolarupnorth7084 Yep, built LFP batterybox with heating.
I saw your eyes sparkle when you looked at those beer plaques! 👍 🍻
It's fun to learn together.
We love you to Andy!
Be safe all
Thanks 👍
In their product specifications, EVE themselves recommends the SOC window to be 10% - 90% for the LF304 and the LF280K. I always wondered how to do that with such a flat curve. Victron's charge defaults for LiFePo4 are 56.8v (3.55v) for absorption for an hour and 54v (3.375v) for float. Based on your recommendations I dropped the absorption voltage to 56v (3.5v) and left the float at 54v for my two LF304 based batteries. My batteries never drop below 50% SOC so I've never worried about the low end. I charge to 100% (56v) every day.
I found the Victron standard settings a bit too high. That may work for batteries which are many years old but not for new ones. If you can charge to 100% anyway every day, I probably would only go to 3.4V/cell as absorption and then set a time for that to like 4h or so... That is even softer and still fully charges them.
@@OffGridGarageAustralia if you have the capacity, go for de less degradation posible thanks Andy and Up North and Personal exelent information
Hey Andy - A test idea for you: Variable discharge rate curves.
Many times we have seen you show us the flat voltage curve of LiFePO4 when discharging (or charging) between 90% and 10% state of charge and with the knees at each end of the SOC.
Most of these show the curve when tested with a constant discharge rate.
I was wondering however what the discharge voltage curve looked like if you programmed a variable rate of discharge, say cycling between 0.1C and 1C for 5-minutes at a time, or some other variable load profile. How much "wobble" would the voltage display when a battery is being discharge with variable rates? You have a battery tester which can be programmed to run such a test I believe.
It seems to me that variable rate of discharge would be a more realistic test of the demands placed on many batteries.
Thanks and keep up the good work.
Thanks Alex. I have tried that in some experiment already and the result was... there was no difference. The think is the Peukert factor for lithium cells is almost 1 so it does no matter with which current we charge or discharge the cells. The curves will look almost identical.
I can do the test with my tester and show you in a future video, no problem.
Thanks for your suggestion.
Seems to me if cells are not perfectly ballanced, Smart Shunt is not enough. It won't protect single cells to go in "unhealth" voltage teritory.
Each cell should be measured and BMS should send commands to charger to lower the charging current. All three of them. Maybe use some kind of BMS system with master and slave shunts capability. Or just rely on three batteryes. If one BMS disconects its battery, the other two are still running, and the system stays on. But if you have just one battery, BMS must comunicate with charger. Only the charger should finish charging, not the BMS (by disconnecting the battery). Can't wait, what is further going to develop in this project. Top work Andy. Respect!
Well my new off-grid hunt camp power system goes active tomorrow. 520 watts of solar panels powering a 40 amp SCC to a 12v 200ah DIY Lifepo4 battery. I've been watching all of your videos along with Will's DIY solar forum and I'm still confused on what parameter settings I should use. You say charge to 3.4 (13.6) but what voltage should I use to start top balancing my battery? Guess I should rewatch some videos to see what I probably missed the first time. Really enjoy your videos and the time you spend finding and suggesting new or better possibilities for this battery chemistry. 🇺🇸☀️🍺
Hey, great setup and design. This should work well. For a rough start:
- 3.45V Absorption, Bulk or Boost voltage in your solar charge controller (different names for the same thing)
- 3.35V for Float (when the battery gets full)
- 3.45V Balancing start voltage (depends a bit on your BMS)
More details coming soon.
Thak You!!!!!
And this has been shop talk with Andy !
excellent as always ... smiles .. beerwah swamp is appearing again above the water line .. the grass has grown deep and the sun is once again shining upon us ... lol..
I agree with Paul, perfect timing.
Just finishing the SFK V3 kits, charging them and in the meantime hanging the new inverter and getting ready to commission Solar V2.0
It's all very exiting Andy and I'm looking forward to the next videos.
BTW, should I be allowing some room in the system for a bilge Pump or is that a Queensland thing?
How was you experience with the Sun Fun Kits? They are really fun, aren't they? The manual is really good and answers all the questions.
The pump... yeah, we have more rain but it's really for the pool actually 😂
@@OffGridGarageAustralia
Can't begin to tell you how much fun it was assembling these batteries.
Everything fitted perfectly, so neat and tidy, so much thought has gone into the design and layout of the components and cables.
Each pack has it's own BMS and they're easy to setup and monitor with the app.
Originally I had planned to put the 16 batteries in series like but after seeing your SFK V3 video this is is the perfect solution for me.
My ageing SLA battery bank is nearly 10 years old, they're doing fine, not their fault we've had no input in the last 5 weeks but when their time is up I'll have no hesitation doing the SFK thing again.
If you think these are heavy, my SLA's weigh 83 kg each, the SFK packs fully assembled are a piece of cake to move around.
Hi according to you what is the best charging voltage of 16pcs connected in series livepo4 ? 😊
Hi, if i had a general lifepo4 charger that charges at a FIXED 3.65v per cell, and it was turned off at a theoretical 70-80%, would this result in significantly less degradation than if it were charged at 3.65v per cell untill 100% charged? Or would the degredation be of a roughly equal amount?
Thank you for all the information 👍👍
Andy, my interest is in a system for my boat and since I don't sail during winter I would like to know if I have to change settings when minimal battery drain ? Come for a sail when it gets warmer. André in Sydney
Hey mate enjoyed your vid and it has given me more confidence to do a full discharge teat on my 280ah lithium nattery bwfore i install it into my 4wd.
I was quite concerned about draining it too low because i might damage it so cheers for that!
Forgove my ingnorance but i guess for a 12v battery i would just multiply the 3.4v x 4 =13.6v as the upper limit and then 3.1v x 4 = 12.4v for the lower limit . . . To keep it within the right range . . . ?
Another thing to consider might be the swelling that occurs while charging and discharging. I don't know how much this physical movement of the cells contributes to degradation, but the swelling on my cells tends to occur more at above 3.35V/cell (26.8/8 cells).
I also consider how long my battery will play my stereo at full volume and whether or not it's long enough to make me happy. Will my hearing be degraded before I need to replace my battery? Time will tell the result of that experiment. You might want to consider/research adding closed captioning to your videos in the long term😁
Thanks for your input. I have enjoyed your videos 👍
The swelling is minimal and often cannot be measured. I'm using my cells uncompressed with some minimal space in between and had some swelling after 1.5 years of using them like this, so the cells actually touched in certain areas.
So you either compress with recommended 300kgf, leave some space between the cells or use flexible busbars, so cells can move without putting force on the terminals.
I like you stereo experiment. That is really outstanding😂
Heya. you made it very clear the why and remember lifipo4 don't have a "memory"
Excellent information Andy, much appreciated. Can’t wait for video series! Are you still experimenting with the GTIL2 grid tie inverter?
Thank, I'm working on these videos now!
Very valuable information Andy. I am glued to your presentations. I have a question. If you have 3 150A batteries (in parallel) charging at 0.2C, would you set the Charge Controller at 30A or 90A ?
Three 150 amp-HOUR batteries, not three 150 amp ones.
Think of it like this (simplified);
In parallel, you have three lanes. Whatever the charger outputs, it gets split up over those lanes. To send 30 amps through each battery, you thus need 90 amps.
In a series connection, you only have one lane going through all the batteries which requires only 30 amps.
Great visionary teacher please compare lithium batteries and Kilowatt labs Super capicitor module. 👍 Thanks 💕💕💕💕
Hi Andy. Great Idea! Please include in to the scope also solar charge controller setings. E.g. where to set a voltage of 3,4? Is this in SCC or BMS etc. Another topic is why not to read state of charge from BMS using CANBUS vs using SmartShunt? Maybe this is clear when you are at battery version 2 or 3, but for those who are at version 1.2 there are a more questions than answers
Yeah, we will go through all the settings soon...
I'm not a fan of communication between BMS and solar charger of inverter. It brings no benefits in my experience and only ads further complexity. It's not necessary.
because of the flat charging and discharging curve (and of course because of your videos about it hehe) at lifepo4, i managed to get from 3.00V to 3,4V (Pack UV is set at 12V and OV at 13,61V) and leave the setting for almost 3 months now and iam good with this. because the new cells always have a higher Ah Capaticy as always (if you buy 105Ah cells the have like 5% +Ah always - i got Grade B BYD 125Ah Cells and measured 135Ah which is more like 5%) - and maybe the battery is keeping longer between these states the charge, so actual i get my full capaticity even when i not fully use the cells. and if they degrade slower because of my treatment, i will longer have these cells before i must replace some of them...