Xuba 280ah Batteries, how to proceed?

I had 16 of the Xuba batteries arrive a few days ago and I would like to hook them up to my solar system (3500 watts, with a Victron 150/100 SCC, 24 volt system).

This is my first set of batteries where I am building the bank, so I am very new to this. I plan to make (2) 24 volt batteries and run them in parallel. I do not have a BMS yet or any specialty equipment for LiFePO4 batteries. My plan was to simply hook them up and start using them in the solar system until I figure out a BMS to use. They all arrived at 3.30 volts and I have this device (Battgo Meter)that checks each cell level and provides a bit of balancing as well.

So the plan is to hook them up, monitor each cell, set the Victron to charge only to 28.2 volts, hook up my Victron low temp sense, which also provides the SCC with a more accurate battery bank voltage, and hook up these low voltage alarm buzzers as well. Additionally, the system will only be in use while I am at the property so it's not a full time thing and will only be on for about 8 hours at a time while I'm there to keep my dog in an air conditioned room, then I will shut it all down when I leave. Also, with the amount of sun where I am, and the amount of solar I have, I doubt the batteries would even come into play (only running a small AC unit while the sun is out).

Is this feasible? Am I doing something completely wrong by not buying a small LiFePO4 charger and charging up each cell to 3.65v individually before use? Is there a big difference in letting the solar charge them up vs. a single cell charger? Any advice is greatly appreciated.

Since these batteries are all new and hopefully manufactured at the same time, it's possible they all have the same internal resistance.

The newer ISDT can measure IR, but not the little BattGO. (https://www.amazon.com/s?k=isdt&ref=nb_sb_noss_1)

The risk you face is having one cell that has less IR and overcharging.

You can mitigate this by not charging the battery into the upper limit.
Set the Victron to 27V top and 22.40V bottom, that is still 95% of the range of the voltage of LiFePO4.

When you very first get them, it's best that they all get set to the same voltage before putting them in series.
You can do this two ways.
Connect them in parallel and they will equalize all on their own passively. It is slow but works perfectly fine.
Get a Charger and charge them individually to 3.3V.

Take a look at the voltage range of LiFePO4:

Well I am in the same dilemma and you can read about it here:


Although I am NOT patient by nature I am forcing myself to slow down and do this right. The $1299 I spent on the cells is a lot to me and I don't want to rush along and ruin my investment. I plan to use these cells for many years to come and figure the extra week waiting on parts to do it right will be a distant memory in the years to come.

I also posted a thread where I debated running without a BMS. I will give away the ending where I finally decided that adding 14% to the overall cost of the battery was a one time insurance payment to protect my investment.

Once I get the battery properly protected I will charge with solar from the get go. That saves me buying a lab grade charger at least.

Many ways to skin a cat but this is how I am proceeding. I will follow along with how you proceed.

Jason makes great points and I think his advice is good. However, I think it would be best (less risky) if you top balanced the batteries in parallel to maximum voltage using a power supply where you can limit the amperage and voltage because you just spent a bunch of money and you don't want to spend a bunch of money on a BMS. Because of the charge curve, you don't actually know the SOC of each cell until you top balance your cells in parallel and leave them in parallel for a few days according to the expert opinion I trust that wrote this article https://marinehowto.com/lifepo4-batteries-on-boats/ . If you follow Jason's idea about not overcharging at the pack level and do a low voltage disconnect at the pack level, a cell level BMS may not be that important. Reading this article written by this expert has given me a solid base of knowledge and helped me minimize financial and personal risks. After I read the article, was also able to sort out good advise from bad advice. Good luck on your project!

jasonhc73 said:

Since these batteries are all new and hopefully manufactured at the same time, it's possible they all have the same internal resistance.

The newer ISDT can measure IR, but not the little BattGO. (https://www.amazon.com/s?k=isdt&ref=nb_sb_noss_1)

The risk you face is having one cell that has less IR and overcharging.

You can mitigate this by not charging the battery into the upper limit.
Set the Victron to 27V top and 22.40V bottom, that is still 95% of the range of the voltage of LiFePO4.

When you very first get them, it's best that they all get set to the same voltage before putting them in series.
You can do this two ways.
Connect them in parallel and they will equalize all on their own passively. It is slow but works perfectly fine.
Get a Charger and charge them individually to 3.3V.

Take a look at the voltage range of LiFePO4:

Lithium Iron Phosphave Charge Range

Sheet5 Lithium Iron Phosphate Charge Voltage Range (LiFePO4) What to charge your cells/batteries/packs to. (SOC),Never More than,3.650,Shown is the "FLAT CURVE" of LiFePO4 cells/batteries/packs. What to not discharge past. (DOC),Nominal,3.200,The steap parts on the left and the right are the "Le...

docs.google.com

Click to expand...

Jason I love this sheet! Is this your work? I like the bms values on the sheet too. I this really important info. Thanks.

Danny said:

Jason makes great points and I think his advice is good. However, I think it would be best (less risky) if you top balanced the batteries in parallel to maximum voltage using a power supply where you can limit the amperage and voltage because you just spent a bunch of money and you don't want to spend a bunch of money on a BMS. Because of the charge curve, you don't actually know the SOC of each cell until you top balance your cells in parallel and leave them in parallel for a few days according to the expert opinion I trust that wrote this article https://marinehowto.com/lifepo4-batteries-on-boats/ . If you follow Jason's idea about not overcharging at the pack level and do a low voltage disconnect at the pack level, a cell level BMS may not be that important. Reading this article written by this expert has given me a solid base of knowledge and helped me minimize financial and personal risks. After I read the article, was also able to sort out good advise from bad advice. Good luck on your project!

Click to expand...

Thank you to the people who responded thus far. I do plan on eventually obtaining a BMS (2 needed), it's just I am new to battery building and still researching how to proceed on that, but need to start using the batteries soon as the temps are starting to creep up and I need that AC unit going in the next month or so.

I need something in the 250 amp range that is 8s. I initially liked the Chargery units but disliked adding in the relays and the draw they use so I am waiting until some of you smart people on the forum get it figured out so I can follow along step by step. Otherwise I haven't really found anything that fits my needs yet. Maybe the Daly units are an option, but I remember Will posting a video about them saying they had low temp cut off, but really didn't. That type of misinformation from a company is a giant put off and makes me not trust them in regards to other claims they make. Maybe I misinterpreted that since it's been a while so I will re-look into those as an option.

I'll probably order a LiFePO4 charger on Amazon and do that top balance as suggested to start things off and then limit the charge from the SCC as Jason recommended.

Do folks think it's also a good idea to have a lower charging voltage?
Example: if your target voltage is 3.3V, actually charge the LiFePO4 batteries using a 3.3V charger.
Is that curve at the top of the charge profile really where the damage occurs?

LiFer said:

Do folks think it's also a good idea to have a lower charging voltage?
Example: if your target voltage is 3.3V, actually charge the LiFePO4 batteries using a 3.3V charger.
Is that curve at the top of the charge profile really where the damage occurs?

Click to expand...

13.8v is recommended by this article written by an expert I trust. Jason also has done an excellent sheet for guidance on bms settings and charge settings. https://marinehowto.com/lifepo4-batteries-on-boats/

Danny said:

13.8v is recommended by this article written by an expert I trust. Jason also has done an excellent sheet for guidance on bms settings and charge settings. https://marinehowto.com/lifepo4-batteries-on-boats/

Click to expand...

I just read the entire marinehowto article. Takes some time to get through but is definitely worth it.

The overwhelming majority of energy you pull from a LFP is between 2.9v and 3.32v as shown in his graph near the end. His graph is from cycle #772 on a battery he built in 2009!

772 cycles and still pulling full 400Ah capacity!! That’s some real world experience and rigorous testing.

2.9v to 3.32v sounds like a sweet spot to me.

Note that my situation is like his. Specifically:

Start with balanced cells.

Low C rate use.

JoeHam said:

I just read the entire marinehowto article. Takes some time to get through but is definitely worth it.

The overwhelming majority of energy you pull from a LFP is between 2.9v and 3.32v as shown in his graph near the end. His graph is from cycle #772 on a battery he built in 2009!

772 cycles and still pulling full 400Ah capacity!! That’s some real world experience and rigorous testing.

2.9v to 3.32v sounds like a sweet spot to me.

Note that my situation is like his. Specifically:

Start with balanced cells.

Low C rate use.

Click to expand...

I'm impressed. You now have access some of the best information available and you have read Rods article at least once! Thanks. I am not an expert as you must know. My experience has been that 3.45 (99.5%) at the top end is was recommend by Rod and it is not a bad guideline. If you look at Jason's charge cure we need to choose a point where the voltage spikes up for a very small increment State of Charge (SOC). It is really hard for our chargers to read precise voltages and discharging could be present etc. At the bottom end we should not be much below 3.2 (20% SOC). Of course, it is more accurate to actual count amps but this could also present problems so we are stuck with choosing points on the charge cure where know we will have good indications of SOC. I enforce these limits with my charge controllers (and shut them off) and low voltage disconnects on my DC loads (Victron Smart Battery Protect) and my inverter (Higher LVD). My BMS has a safety backstop like Jason has 3.375 ( Mine 3.5) and 3.15. My cells have remained in balance as long as I stay below the top limit of 3.45. Many people don't agree with Jason and I. We are not in the majority so you can look around and see arguments of others who buy 3.6vpc chargers and let them rip. The majority may also be more concerned with balancing that I (and maybe Jason) don't need to worry about. You will need to decide for yourself based on evidence but I tell you now, we are a minority.

Yes. Towards the end he states how little energy is to be had above 3.32v per cell. That is the section with the graph from cycle test 772.

The Chargery BMS 16T cannot accept an upper limit lower than 3.4v so 3.4v is my upper limit now set to stop charging.

If this thread is still active, I'll second or third the use of 3.45V or so as a great target voltage. One difficulty is charge rate. If your rate is low (0.05C or so), then the cells are approaching full capacity as they get above 3.4V so hitting 3.45V and holding for a short absorb will get you very close to 100% charge with no worries about overcharging as long as your cells are all within 100mV of each other. If your charge rate is high OTOH, then 3.45V may only get you to 90%. There are so many variables, it's difficult to have a one-size-fits-all approach. A steady consistent charge will get you a different SOC than the same charge rate that is intermittent (like cloud - sun intermittent). A final complicating factor is the SOC that your charge cycle starts at. If your cells are fairly discharged and work back up to nearly full over a few cycles, the first time they hit target V it will likely take longer to finish charging (you can see that by the rate the charge current decreases over time) than it will on a day when you're only charging back from a minor discharge.

DeeK said:

If this thread is still active, I'll second or third the use of 3.45V or so as a great target voltage. One difficulty is charge rate. If your rate is low (0.05C or so), then the cells are approaching full capacity as they get above 3.4V so hitting 3.45V and holding for a short absorb will get you very close to 100% charge with no worries about overcharging as long as your cells are all within 100mV of each other. If your charge rate is high OTOH, then 3.45V may only get you to 90%. There are so many variables, it's difficult to have a one-size-fits-all approach. A steady consistent charge will get you a different SOC than the same charge rate that is intermittent (like cloud - sun intermittent). A final complicating factor is the SOC that your charge cycle starts at. If your cells are fairly discharged and work back up to nearly full over a few cycles, the first time they hit target V it will likely take longer to finish charging (you can see that by the rate the charge current decreases over time) than it will on a day when you're only charging back from a minor discharge.

Click to expand...

I did 3.4v which worked great too. I think you could go as low as 3.36v successfully with 0.0001C. amperage fell off surprisingly quickly.

If one wants to just put their batteries into service I think they could charge them until one cell gets to 3.4v then set their float at that voltage. Then perhaps having an active balancer slowly balance. They could come back ever week or two to increase the voltage until it was all even.

zorlig said:

I did 3.4v which worked great too. I think you could go as low as 3.36v successfully with 0.0001C. amperage fell off surprisingly quickly.

If one wants to just put their batteries into service I think they could charge them until one cell gets to 3.4v then set their float at that voltage. Then perhaps having an active balancer slowly balance. They could come back ever week or two to increase the voltage until it was all even.

Click to expand...

That's very similar to the approach I took at the beginning. I couldn't push the bank much above 3.4V (54.4 bank voltage) early on or I'd have some groups pass 3.45V and then runaway while others were not yet chargedm(hadn't reached 3.4V). Over time with the help of a 10A active balancer and by getting my groups better matched according to capacity, I can now easily push the bank to 55.2V with the maximum bank differential staying below 60mV typically. Patience was the main virtue!

DeeK said:

That's very similar to the approach I took at the beginning. I couldn't push the bank much above 3.4V (54.4 bank voltage) early on or I'd have some groups pass 3.45V and then runaway while others were not yet chargedm(hadn't reached 3.4V). Over time with the help of a 10A active balancer and by getting my groups better matched according to capacity, I can now easily push the bank to 55.2V with the maximum bank differential staying below 60mV typically. Patience was the main virtue!

Click to expand...

Yeah I did much the same, except I had a very show charge rate with the UPS I'm using now, my 2A active balancer did half the word and I manually charged low cells that were next to each other. Patience won the day!