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Lithium batteries

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Mark_J1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark_J1 Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2024 at 11:30
Thatís a generic table for LiFePO4. On batteries with Eve cells from LifeBatteries.co.uk and batteries from Fogstar.com (canít remember the cell make) it maps very well. 

If the issue you are having is the mapping between SOC and voltage, then Iíd politely suggest itís not really an issue. The SOC value is often wildly inaccurate. Even for 2 batteries in parallel, the 2 BMS will regularly show different SOC values due to very minor differences in resistance, cell matching and over-volts point. Any monitoring you have of the bank will struggle even further. 

Rely on the voltages at the BMS level. If you are used to LA batteries, it can genuinely feel a bit weird. Your sense of the Ďright voltageí v capacity will be way off as tiny differences in cell voltage make a huge difference in how near full the battery is. Takes a little getting used to :) 

Btw in my case, for battery longevity, I have BMS battery max volts cut-off at 14v so I deliberately leave a % or 2 off the top end of the battery. I still see 100% on battery SOC. The algorithms are really not that clever in practice. 

Mark





Hanse 400e "Grey Goose" Hull #31
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ariette View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ariette Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2024 at 15:53
Dates
Congratulations on your new boat, mine is on its way also with your lithium setup. Question for you can you set the BMS at say 14v (as above) using the Mastervolt charger or do you need to do it at the Lifos level using their Bluetooth controls. ( There is some active chatter about how reliable Bluetooth is for this sort of control). Thanks. Mark
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark_J1 Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2024 at 19:26
Ariette - this is all my learnings. Like all things internet youíll find plenty of range in the opinions!  However, Iíve used this logic in the real world and been delighted with my LiFePO4 solution. 

You manage LiFePO4s at the BMS level ideally. Most have the BMS onboard the battery, some like Victron have a separate BMS but the logic is still the same. Low & high volts cut-offs and other Control parameters are managed in the BMS. That said, not all batteries have a fully adjustable BMS. In that case the workaround is to have the control logic in the charging circuit. However the downside is then you need to mirror that across all charge sources (alternator, solar, wind, hydro etc). Hence why you want control in the BMS. 

The charge side can actually be pretty dumb. Just provide 14.4v bulk and 13.5-13.6 float. Absorb is irrelevant. 

Mark
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Darek View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Darek Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2024 at 20:33
this is really good valuable discussion, thanks guys Smile

I must admit I'm overwhelmed with your knowledge. So far I didn't touch any settings in MasterVolt and the app to access BMS in individual batteries from Lifos (manufacturer) is readOnly to my knowledge. So I don't know how to change any settings yet and I assumed the factory settings are optimal. 

I was also told there are different charging sources (with separate hardware circles) like MasterVolt and alternator...and Mark rightly added solar, wind, etc... In that case it would make sense to have a good charging setup on BMS level. And I hope I will be able to do it.

So far my dealer is still busy with investigation regarding the 13.2V - is my service battery fully charged with this voltage? or is it 70% SOC?
Darek "Summertime" Hanse 460 #92
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Yoda Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2024 at 21:06
After several seasons of using LiFePo4 batteries that I have built myself I have found the only real indicator of SOC is from a decent Battery Monitor such as the Victron BM702 that uses a good quality shunt. The flat charging curve makes the relationship between voltage and state of charge very unreliable over the majority of the capacity range. Only at the very top and bottom of the curve does voltage start to indicate more accurately where the SOC is - the very place you don't really want to be with the battery. 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Darek Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2024 at 09:17
I have results of recent tests: 2 batteries out of 6 are broken, they show 7V and 8.5V respectively. We disconnected them from the bank. It is also worth to mention that we couldn't connect to theirs BMSs via Lifos app, so they are definitely broken.

The remaining 4 batteries seem to work fine and their BMSs report 99% SOC with 13.24V as an example. We continue testing them but the initial conclusion is that the low voltage around 13.2V is a normal voltage for Lifos batteries for 100% SOC.

Another finding is that 6 batteries are connected together and Lifos allows to connect up to max 4, as per technical specifications. The dealer will request Hanse to provide official statement that installed setup is ok and doesn't have impact on 5 years warranty from Lifos.

We will also claim the 2 faulty batteries
Darek "Summertime" Hanse 460 #92
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