Lithium Battery Charge Voltage versus BMS Battery Voltage Cutoff

[chrisski]

I have ordered Eve 280 amp cells to make 24 volt batteries. I am planning on ordering one BMS for each 24 volt battery. I am looking at Overkill BMS 100 amps at 24 volts. I don't have either product yet, but am reviewing spec sheets for the build?

My question is, the Eves are supposed to be charged at 29.2 volts, but the overkill BMS has Battery Over Voltage at 29 volts. If I set my charge controller to 29.2, does the BMS stop charging when charging voltage reads 29?

This 29 volt limit seems to limit the batteries to .2 volts short of a full charge. Perhaps the charge curve for lithums is so flat that when it starts to spike, this is insignificant.

 

[time2roll]

Yes, there is very little additional gain above 27.6 to 28.0 volts. 29.2 would be the absolute maximum to be applied to the battery. Not the same as minimum charge voltage.

The BMS is there to be the final protection of the cells.... not to be the charging cut off on a regular basis. I would set your solar controller a bit lower.

 

[Steve_S]

IF you charge LFP to 29.2V / 3.650Vpc your maxing the limits and will have runners hit 3.65 before the rest of the cells which will trip the BMS. GUARANTEED ! It is really pointless to charge above 3.525 and the cells will settle to that within an hour of thecharge stopping at 3.650Vpc.
Above 3.5 and below 2.8 is only 5-7% of whole capacity which is usually reserved off anyway. The main working range for LFP is 3.000-3.400 hence why Nominal Voltage is 3.200 (50% SOC) which is where 90% of the power lives. Below 2.900 is the cliff fall and above the 3.450 is the Cliff climb.

Bulk 280's typically test out between 270-282AH capacity from 2.500-3.650.
Matched & Batched 280AH cells are testing out between 285-295AH for the same range. One of the differences which people are only Just now realizing.

3.650 is the Max Allowable Voltage NOT the Max Charge Recommended state.
Below are my setting which work the treat on both Bulk Commodity & Matched & Batched cells and even the nasty recycled EV-LFP cells which are quite finicky (the Shunbin cell mess).

All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.
(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
** Coulumbic Efficiency for LFP is 99%

 

[chrisski]

All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

I appreciate your reply. I just ordered my cells yesterday, so it could be 10 weeks before they come in. I haven’t got a delivery date, but I expect the beginning of September. I will spend a bit of time looking at what you wrote and what is in your signature block.

My Victron charge controller I already have does not have a “boost.” Min volts and max volts I recognize of the Overkill BMS I plan to buy, but I don’t see a “rebulk” voltage or a “end amps”

I will take a look at the calibration portion.

I had been looking at purchasing some equipment yesterday to do tests. My plan had been based off Will’s video of top balancing cells. Using a 26 amp lithium charger I already had, I was going to arrange my cells in 12 volt configuration and charge them. Then, I was going to connect all 16 cells in parallel and use a DC adjustable voltage 10 amp charger to top balance the batteries at 3.6 volts. Then I would take all the cells out of parallel configuration and use a capacity tester on each cell one at a time to see the capacity of each cell. After that I’d have data on each individual cell and use this to assemble the cells into two batteries of 8 cells each. After both batteries are built, I’d charge the cells and top balance again, and then install.

 

[Steve_S]

I appreciate your reply. I just ordered my cells yesterday, so it could be 10 weeks before they come in. I haven’t got a delivery date, but I expect the beginning of September. I will spend a bit of time looking at what you wrote and what is in your signature block.

My Victron charge controller I already have does not have a “boost.” Min volts and max volts I recognize of the Overkill BMS I plan to buy, but I don’t see a “rebulk” voltage or a “end amps”

I will take a look at the calibration portion.

I had been looking at purchasing some equipment yesterday to do tests. My plan had been based off Will’s video of top balancing cells. Using a 26 amp lithium charger I already had, I was going to arrange my cells in 12 volt configuration and charge them. Then, I was going to connect all 16 cells in parallel and use a DC adjustable voltage 10 amp charger to top balance the batteries at 3.6 volts. Then I would take all the cells out of parallel configuration and use a capacity tester on each cell one at a time to see the capacity of each cell. After that I’d have data on each individual cell and use this to assemble the cells into two batteries of 8 cells each. After both batteries are built, I’d charge the cells and top balance again, and then install.

If you ordered the Matched Cells from Luyuan, you will also get access to the Cell Testing Report from the process which makes it much easier to group the cells up nicely, they are also coming in capacity tested typically at 285-292AH capacity and very consistent IR levels throughout cycle.

Terms used by manufacturers vary (what a PITA), the settings are usually comparable just the naming conventions & the data format. Example, a BMS may have an AH Rating and a kWh Rating or even just a WattHour rating... sometimes the data format is in MA or MV, Sure makes it a PITA for DIY'ers because it can create even more confusion, as if there isn't enough as it is. (reminds me of the early PC days of the mid 1980's, oivey that was hard on folks)

 

[chrisski]

I bought these new version Eve 280 ah off the Luyuan Website from Amy

1pcs Eve 280ah Lifepo4 (lfp) 3.2v Cells Battery (new Version Lf280k With 6000cycles,Fully Matched)--genuine Grade A - Buy Eve lifepo4 280ah Product on Alibaba.com

1pcs Eve 280ah Lifepo4 (lfp) 3.2v Cells Battery (new Version Lf280k With 6000cycles,Fully Matched)--genuine Grade A - Buy Eve lifepo4 280ah Product on Alibaba.com

www.alibaba.com

I think these are the only version she has for sale now. The other 16 Eve cells I requested a quote on she had me request the quote off the individual cells.

If there had not been other people before me who had ordered from alibaba with this company, I would not have ordered there. Like you were saying, the way the specs were listed did not translate perfectly and the in the category of batteries on Alibaba, these were listed as Lithium Ion, not lithium iron phosphate which is two different things,

 

[Steve_S]

LOL, Amy had a junior do the website, it will be fixed. In fact I am talking with her right now... She is editing all of her listings right now as I write this and checking to make sure they are consistent and correct. It takes a while because the Ali* sites are not easy/simple to change, kinda clutsy I'm told.

YES, those are the Right Ones, Matched & Batched new gen cells. You will certainly appreciate how nicely they behave... I am NOT an easy person to surprise or impress but my first Matched Batch did just that.

 

[chrisski]

Thanks. I’m happy to hear that about the batteries. If not for all the mentions on this site and a Recommendation from another member, I would not have ordered from her.

With that first Ali Order, I got a fraud alert from my credit card and approved the transaction. The charge did not appear in my pending s like it normally did, but ali said the transaction could take an hour or two to post. A half day later, I called the credit card company, and the credit card company ignored my approving the transaction with the text reply, and needed a phone call and told me to order it again, so the second time the order went through.

 

[Steve_S]

Ohh the CC issues happen to a LOT of folks. Some cards are more picky and even downright dumb in some cases. You aren't unique with those issues. My own had several issues at first but now it's been worked out and they don't do stupid to me anymore (they have a thing on the file for it). Can't blame them for working to protect their clients even if it creates a bit of PITA... heck of a lot less hassle/effort than trying to chase recovery funds and all that miserable stuff.

 

[Steve_S]

BTW, I just went and looked at the Luyuan Listings... Amy fixed them ALL, normalized the listings for consistency & clarity AND the MOQ messup is fixed to show an MOQ of ONE as opposed to TWO which confused many people.