I am sure there are many who have already done the calculations and some experiments, I am not one of those, but I have been doing the same as you, reading other information and watching videos Here is what I think I have learned and where I am leaning to go: 1) Your 12.8 to 13.3 charge/discharge range seems in line with others 2) Adding a 12 volt, lead-acid battery into the bank via an isolator that regulates that charge/discharge between the LFP and Lead-acid 3) Trying to find the correct ratio of Lead-acid to LFP for best efficiency Hope that helps jump start a conversation for all of us to learn, keep up the good work!

@TheCrazyRomanian

7 ай бұрын

Dude that's crazy, I'm going to pin this one because I know it's wrong but I'm sure the people will love to read and give their opinion on it I hope you're ready 😁

@toyeeb

7 ай бұрын

I read somewhere that Lifepo4 and Lead acid in parallel works because the lead acid will keep trying to bring down the voltage of the Lifepo4 to close to 12.8v which is the resting voltage of Lead Acid. They have to be around the same SOC(100% full charge using same charger) when you initially connect the two different battery chemistries in parallel. It is advised that a smart charger that doesn't have equalization feature be used so the mixed battery bank stopped charging at a specific voltage(like 14.4v).

@Tumbleweed5150

6 ай бұрын

From all my studies, I personally would NEVER use lead-acid with my LiFePO4 batteries! The only time this is useable is if one gets a DC to DC charger that allows one charge the LiFePO4 battery bank from an alternator.

Voltage of LiFePO4 batteries cannot be used to calculate SOC. It is impossible. Once the voltage in the cell rises above 3.4V, you're already at 96%SOC or above. Below that, there is no way to tell if the cell is at 80%SOC or 40%SOC by just measuring the voltage. These LFP cells have 6000cycles+ at 100% DOD, so fully cycle them once a day will give you 16+ years. Then they have reached 80%SOH. Forget about the 20-80%SOC rule. This was important with Li-ion cells, but not with LiFePO4. Charge them to 3.45V/cell, let them balance for 30min and drop the voltage to 3.35V/cell (Float). They will last forever. At the bottom, when they hit 3.0V, you have about 7% capacity left. That's when I stop discharging (if the batteries ever go that low).

@philbrooke-little7082

6 ай бұрын

I have found that, so long as the battery isn't charging and has a low rate of discharge, you can get a good approximation of SOC from resting voltage but you are looking at 100ths of a volt rather than 10ths. The JBD BMS has a lookup table so that it can guess at an SOC when it can't coulomb count. Certainly I agree that while charging the voltage is fairly meaningless as there is another variable affecting the voltage, namely current, which distorts an already pretty flat 'curve' On my BMS I did a voltage based guessometer of SOC based on the curve being relatively straight (not flat) between 12.8v and 13.4v with the algorithm only having a look if there was no charge and the discharge was below a certain amount. It tallied fairly well with the actual coulomb counted SOC which I know to be accurate, particularly in summer with daily full charges to synchronise it. Ps I do watch your channel and have got some useful info from your experiments to help inform my own and I thank you for that.

@TheCrazyRomanian

6 ай бұрын

Great advice

@alanblyde8502

6 ай бұрын

I’m ganna give that a go Andy

I think you can come up with a better gift for your grandchildren than 20yo LFP battery. :) Run it 100-0 and forget about this micromanagment. Why? Because - maybe you forgot - the 3000 cycles of "life" does not mean that then the battery is dead. This is the rating of getting to 80% original capacity. It's still usable.. for another 5000 cycles easily after that.

@TheCrazyRomanian

6 ай бұрын

Best advice ever .. you are the man

The problem with charging to 13.3v (26.6v) is that this is the resting voltage for 80% you have to have a voltage overhead on your charge system to be able to get there. One of the great advantages of lithium is it’s ability to accept any charge that’s available but to do that it needs some ‘push’ (voltage) behind it to get it in. I use solar mainly and occasionally the engine but when charging at reasonable rates, say a good solar morning, the voltage rises noticeably higher to get the available power in and then, when it stops, the voltage falls back to reflect the state of charge. I have found the best compromise cut off voltage to be about 14v. If charging with the engine at around 0.25C (200A into 800Ah) then I increase this to 14.2v and this gives around a 90% SOC by the time it cuts off when the voltage then drops back to one that reflects that SOC. I datalog my system every minute and have been doing so for around 4-5 years and have used this data to determine the setting that give least stress to the batteries along with best charge acceptance. The aim is to get away from the absorption current taper of lead acid that wastes so much charging resource. At the moment for instance the batteries are at around 80% with a 0.025C charge rate yet are at 13.4v. I think you are probably having a max charge of somewhat less than 80% with the other risk which is that you never get the cells into the top ‘knee’ which is where they need to be to balance. I have a 12v low voltage disconnect but with a recommendation to start charging at 12.8v or 20%. I use a home built BMS to give me quick easy access remotely to change any parameters and because I also wanted to look at protecting from low voltage overcharge which actually turned out not to be a problem with the settings I use. I hope you find some of those thoughts useful. I have a home built battery of various cells in multiple P4S with about 2500W solar and around 200A alternator charging as a backup. I also run hybrid with a 12v lead acid however that is only there to stabilise the charging sources when the BMS cuts charge and enables me to use lead acid charge setting on everything so saving cost in the conversion from lead acid and enabling alternator charging which would otherwise have needed either dc-dc converters (work of the devil) or expensive alternator controllers.

@TheCrazyRomanian

6 ай бұрын

That's great info .. Yes that's what I've set up my charge controller to stop 27.8 It seems to be the magical number with mine but I think it's about 0.2 off my voltmeter so basically we are in line with what you were saying, unfortunately when I set up my charge controller in lithium iron phosphate mode it only has a charge voltage and that's it It doesn't give me any floating or bulk or any other stuff

@philbrooke-little7082

6 ай бұрын

@@TheCrazyRomanian You don't actually need float although if you do have a charger with it then 26.6-26.8v would be about right. It is important that the charge gets cut at your set voltage and not held there. Some controllers with a "lithium profile" just hold the voltage there and don't disconnect. This is why I tend to say to people that they need a 'valid' lithium profile as many simply are not and don't do the battery any favours. "Bulk" is actually not a setting, its a state before the absorb / boost setting is reached and is the 'constant current' part of the charge cycle where it charges with whatever current is available until the 'absorb' voltage is reached when the voltage is regulated and, as a consequence, so is the current. Some controllers can be used on a lead acid setting so long as you can control how long it stays in absorb for (a few minutes is fine) and also control the float level (26.8 / 27v or so) and also control the boost / bulk reconnect which can be just below float.

Run down to 12-12.2 charge to 13.8 The problem is you can’t really utilize voltage as a reference with this chemistry until your within 10 to 15% of empty or full.

@TheCrazyRomanian

6 ай бұрын

good advice ! I like it

It is a reaaaly useful information for who think about to buy them and set a system at home... Thank yout

I got a 25.6V 150Ah LFP battery. I usually discharge it to 50% of its capacity every day, and use the grid until the next morning. I have programmed the Grid Disconnection feature to switch to solar at 26.8V, and to grid at 26V. While discharging, it is not accurate that it will be at 50% DOD at 26V everytime. If there is around 300W of load, it is almost close to 50%. But if I put double the load, say 600W, the voltage will drop faster, and I will switchover at 40% DOD or 30% based on the amount of load on the battery. During charging, I set the Bulk to 28V and the float to 27.2V. I loose around 10 Watts of charge when the voltage drops to 27.2V from 28V. I can set the Bulk to 27.2V, but the problem is during the charging, I get around 500W - 1000W depending on the load that is used in parallel. At 27.2V, at 60% state of charge, I will not be able to push more than 500W into the battery, and the MPPT will have to adjust its Solar MPP to reduce the power harvested from the solar. During Cloudy days those few moments where the suns pops out of the clouds and shines on the cool panels for couple of minutes, the 28V Bulk will help me to dump all the power coming from the solar into the battery without any limitation, as it can take 80 Amps of charge. Every LFP battery is different, so the Bulk, and Float voltages needs to be set based on the internal resistance of the battery.

@TheCrazyRomanian

6 ай бұрын

My charge control doesn't even have options to set any other things when it's set up into lithium so there's no float there is no absorption It's just stop charging at this voltage and stop using the battery at a certain voltage and that's it

1:00 LiFePO4 batteries, when bought with their own BMS, are set to top balance the cells inside at the top of the charging cycle: 14.6 on a nominal 12V system, or 29.2 on a 24V system. If you don't charge them up to full for at least two hours at least once a week, they can get way off balance, which will REDUCE their total lifetime. Not using them too low WILL extend their life, though. Most of these batteries are rated for at least 10 years, and that is if one charges and discharges them fully each day. I designed my system so that the battery bank will hold over 80% capacity most of the time. I only see lower capacity in the middle of summer when I use my larger air conditioner most of the day. I am living in an off-grid community in the Southern CA desert, so we do rely on the systems I've designed for my RV, my work truck, and my girlfriend's shuttlebus, especially when it can get over 120F here!

@Tumbleweed5150

6 ай бұрын

When I was designing my 48V system, I planned on making my batteries last around 20+ years.

@TheCrazyRomanian

6 ай бұрын

Great info .m thank you

@TheCrazyRomanian

6 ай бұрын

Wow ambitious

Consider cell balancing. Usually balancing only happens as the batteries pass 95%. You cannot go many cycles before an unmatched battery of cells starts to unbalance. Only you and your set of batteries can tell how much balancing your cells need.

@TheCrazyRomanian

6 ай бұрын

Some batteries have cell balancing , also there are boards you can buy that take care of that on the fly ..

@TheCrazyRomanian

6 ай бұрын

But yeas cell balancing is a thing ..

I have some 36 volt battery packs. I am wondering if the inverters in this particular setup will run and produce a/c power with 36 volt battery packs.

@TheCrazyRomanian

6 ай бұрын

No. This model can't .. they are picky on voltage 24 to 31 volt max

I've been looking for any info. You are the only one I've found asking questions. Can i keep my batteries 100% charged on solar?

@TheCrazyRomanian

2 ай бұрын

Yes you can , these batteries are super durable

@frederick6008

2 ай бұрын

@TheCrazyRomanian thanks, you're the only one to answer. I've been reading manufacturers info and asking others no one can say for sure but, i have not found one manufacturer who warned against it. When I'm not using the system i disconnect all inputs. When i am using it even sparingly i leave the solar charging. It frequently hovers at 90-100%.

@frederick6008

2 ай бұрын

@TheCrazyRomanian was thinking, RV's have solar connected all the time don't they. Maybe that's why they burn sometimes. I just don't trust these batteries quality enough to leave the solar connected.

I am not extremely knowledgeable about the chemistry in these batteries, but my intuition says it would be useful to charge to 95-99% about every 10th cycle (day), just to keep their capacity fully exercised. Likewise, they should be ran down to 20% every so often. I think Lithium Ion battery experts say that, and it should be similar for LiFEP04 chemistry.

@TheCrazyRomanian

6 ай бұрын

Yes that's good information and I think lithium iron phosphate are a little bit more durable and less picky than lithium ion

Yeah, unless there's a good reason why something performs better when it is pushed to a limit, it's best to give it a nice buffer to ensure that it lasts longer. Lead acid batteries need to be charged at a higher voltage and then maintained at their full voltage or they degrade. You can do so with a LiFePO4 battery as well, but doing so degrades it faster than giving it a gentle charge and discharge.

@TheCrazyRomanian

6 ай бұрын

Interesting info

@Tumbleweed5150

6 ай бұрын

You are partially correct. Charging a LiFePO4 battery at the limit of 50% Capacity can lower the lifetime, but if you charge it at 20% Capacity, will allow it to last longer. Discharging at a lower rate is probably a good idea, but not as important as charging at the lower rate.

Did you buy 4 different brands of batteries just to test which are better than others? Or did you just go with whatever the best price was?

@TheCrazyRomanian

6 ай бұрын

I was looking for deals and when the sales came I got more so that's how I ended up with different brands

According to the Voltage/State of charge chart from Battle Born Batteries, 13.6V is 100% resting, and 14.4V is 100% while charging. I believe you need to do more research!

@TheCrazyRomanian

6 ай бұрын

Good info

Just use batteries as a buffer. Put most of the electric load on daytime. Invest in low power applience for eveing would be cheaper.

@TheCrazyRomanian

6 ай бұрын

Not to mention get rid of my wife she has a TV running on some stupid aquarium with fish in it 🤣 at this point we'll be cheaper to just get fish

I started with a large 48V battery bank and i wish i had gone with 24V and fewer batteries. 1) Higher voltage chargers and inverters cost disproportionately more than lower-voltage chargers. 2) I experience far fewer power failures than expected, better to invest in infinite-shelf-life propane and a propane generator.

@SUNofNY

6 ай бұрын

Batteries are best for storing energy from an infinite supply like the sun. Propane may have a long shelf life, but it gets used up very fast when there is no resupply, and it is not rechargeable.

@TheCrazyRomanian

6 ай бұрын

Great info

The price of these batteries is falling all the time now! Personally I’d rather capture the energy from the sun ☀️ 😊

@TheCrazyRomanian

6 ай бұрын

That's the best way

go full ham and spend $10k for 31kwh of batteries/rack ... run for 10 years ... $85/month ... 16 years ... $52/month ... adjust these numbers for your requirements ... put whatever $ amount you come up with in your solar savings account ... the $ will be there waiting for your next round of batteries ... do not sweat the details

@TheCrazyRomanian

6 ай бұрын

I actually only need about 10 kilowatts a day because the sun shines half the day here in Vegas so very rarely is cloudy and the 10 kilowatts last me throughout the night easily but my family is small and I don't have an electric car

okay okay ... do not go full ham ... build your own with eve 280ah raw cells ... build 3 batteries for $6000 which equals 43kwh ... now what are you looking at? ... 10 years ... $50/month ... 16 years ... $32/month ... and if you only build 2 batteries for 29kwh ... holy hell ... $4000 ... 10 years/$33month ... 16 years/$21month ... lol ... crazy

@TheCrazyRomanian

6 ай бұрын

Good breakdown