Hey All, first post. Exciting, bought 24 Eve LF280K and 3 JBD AP20S003S 200A bms from Docan Technology, Houston, in March. Got 3 8S strings operating w BMS, 1 installed replacing 3rd set of L16s in existing 20yr+ off grid room temp home system. Operating per Eve datasheet 90%-10%, charging to 26.6v/3.3v/cell. Overnight use of 30-70ah measured by Trace Meter TM500 w/Deltec shunt. 60ah commonly, just over 20% of 280ah string. Don't understand why every morning string voltage is 26.1v/3.26v/cell. Going from 90%soc to 35%soc is 55% reduction instead of expected 20%. Haven't been successful w/bluetooth, different post later, so stock, no programming changes, no disconnects, BMS just sits there, as it should, totally within operating parameters,...balancing? JBD bms datasheet shows 100ma@3.32v, 180@3.35v, and 260ma@3.38v, less than results showing. These have the contactor, coil only 35ma typically/50ma max, maybe 1ah overnight? Finally got other 2 strings added, 840ah and 3bms total and the results are unchanged 26.1v/3.26v/cell every morning. Having 840ah meant to carry you through several days of cloudy MT weather is lost when you are down to 35% every morning and last night only used 29ah, 31ah after 2 cups of jo! They do balance, cells within .01v at any soc. Trace meter 20yr trouble free, xchecked w/multiple digital voms, all charge/discharge goes through meter/shunt except what is internal to the bms units. At a loss, thinking of the wealth of knowledge here, surely someone has had similar experiences? Any ideas? Disable balancing except for once/mo? My thanks in advance.
JBD 200A Possible Excessive Battery Drawdown
- Thread starter Jdubya
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42OhmsPA
What's in a title?
What inverter are you using? What's the idle consumption, did you account for it?
Hi, A Trace sw4024, again 20yr troublefree, "on" idle in book is .66a. For overnight say 10ah. I can't account for 55% of 280ah, more now that it is 840ah. The Trace meter shows reasonable amounts through the night, 6-7-8a most of the night, 10ah total? Coming in to daybreak today was about 2a, maybe half that for the inverter with the fridge off. Obvious use coffee, 25a, microwave and air fryer together 150a, but those are usually short term, and not much at night. The common denominator seems to be the bms, whether 1 string w/bms or 3 strings w/3bms.
RCinFLA
Solar Wizard
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You need to re-setup the battery 'full' voltage in TM500 to 28.0vdc.
The best voltages depend on how you use inverter. For off grid, set float to 3.45v per cell or 27.6v.
Balancer should be set not to start balancing below 3.4v per cell and absorb should be 3.50v to 3.55v per cell, 28.0v to 28.4v with a two hour absorb time. This ensures some balancing time. If on PV and absorb cycle is triggered several times a day cut down absorb timer so you average a total of about 1 hour absorb voltage time per day. If you start balancing below 3.40v per cell you are more likely to imbalance cells.
From a generator recharge take to 28.4v absorb.
You have two options for absorb or equalize for pack balancing. If you want to manually balance you can setup equalize to do a 28.4v manually initiated equalization charge cycle for 2 hours. This will do manual initiated balancing on batteries Do it at least once a month. Leave absorb settings same as float setting, 27.6v. This will give less stress of repeated absorb cycle voltage while allowing you to ensure you balance cells periodically. On PV you have to ensure when you do equalization charge you have the sun power to hold the 28.4v for two hours. Your running power consumption may eat into this balancing time. This is the down side of using a manual equalization charge to do balancing.
The best voltages depend on how you use inverter. For off grid, set float to 3.45v per cell or 27.6v.
Balancer should be set not to start balancing below 3.4v per cell and absorb should be 3.50v to 3.55v per cell, 28.0v to 28.4v with a two hour absorb time. This ensures some balancing time. If on PV and absorb cycle is triggered several times a day cut down absorb timer so you average a total of about 1 hour absorb voltage time per day. If you start balancing below 3.40v per cell you are more likely to imbalance cells.
From a generator recharge take to 28.4v absorb.
You have two options for absorb or equalize for pack balancing. If you want to manually balance you can setup equalize to do a 28.4v manually initiated equalization charge cycle for 2 hours. This will do manual initiated balancing on batteries Do it at least once a month. Leave absorb settings same as float setting, 27.6v. This will give less stress of repeated absorb cycle voltage while allowing you to ensure you balance cells periodically. On PV you have to ensure when you do equalization charge you have the sun power to hold the 28.4v for two hours. Your running power consumption may eat into this balancing time. This is the down side of using a manual equalization charge to do balancing.
Hi RCinFLA, Thanks for all the info, my apologies for not getting back sooner. I've seen those figures before but not on the EVE battery product specification sheets other than 3.65v cutoff. It does identify Recommended scope of SOC, 10% - 90%. EVE doesn't specify the 90% voltage but most I have found are 26.6v/3.33v/cell and one reliable source also mentions 26.8/3.35 @ rest. Higher voltage will of course charge faster but I haven't found why that is necessarily "better". To me it is less right or wrong and more about choices one makes for priorities and the lower voltage is supposed to equate to the priority of a longer life. My old Trace C40 doesn't have an hour choice but the generator powered inverter/charger does except that with the new batteries it hasn't been run once.
I agree with you about balancing @ a higher voltage but don't yet know either what the bms is doing or what it can be adjusted to, not having seen an operation manual. Probably best for me to ask the folks @ jiabaida. I have an Epever 60a in the works along with rewiring the panels that might accomplish the higher voltage and accomplish intermittent instead of what appears to be constant daily balancing. Next project, thanks again.
I agree with you about balancing @ a higher voltage but don't yet know either what the bms is doing or what it can be adjusted to, not having seen an operation manual. Probably best for me to ask the folks @ jiabaida. I have an Epever 60a in the works along with rewiring the panels that might accomplish the higher voltage and accomplish intermittent instead of what appears to be constant daily balancing. Next project, thanks again.
RCinFLA
Solar Wizard
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If you long term run with misbalanced state of charge cells you wear the cells at differing rates and get less extractable capacity from battery array. This results in more mismatching of cells which causes even more uneven aging on cells. The more mismatched the cells, the harder it is to keep them in state of charge balance. It is a compounding downward spiral of cell performance.
The wider the state of charge range the cells are cycled the more expansion and contraction of graphite negative electrode. The more expansion and contraction the more damage is done to the solid electrolyte interface protective layer. This protective layer is grown initially when a cell is new and is initially grown by manufacturer process after cells are fabricated. It is called the initial charge forming process.
The SEI layer is a thin coating over negative electrode graphite granules that retards electrons from escaping the electrode material into the electrolyte. When electrons enter electrolyte, it causes decomposition of electrolyte. Electrolyte decomp creates gases and tars as its byproducts. Tars clog the electrode pores that restricts the flow of lithium ions through cell, increasing cell impedance.
Fracturing and repair of the SEI layer is a normal part of cell aging process. Cracks are repaired during subsequent charge cycles. The fractures in SEI layer does allow some additional electrons to escape into electrolyte during charging and the repair action consumes a little of available free lithium ions that reduces cell capacity over repeat cell cycling. Again, part of normal aging process.
Maintaining a higher state of charge results in more electrons overcoming the SEI protective electrostatic barrier to escape into electrolyte resulting in additional damage to electrolyte. Overcharging, especially above 4.3v on a cell, allows a large amount of electrons to escape electrode creating a lot of damage to electrolyte. Most visible result is cell bloating, although the real damage is the tar clogging electrode pores.
Almost all BMS's restricts cell balancing to a cell voltage above 3.4v. This is point where cell is approaching full state of charge and has an accelerated rate in rise of cell voltage which makes it easier for BMS to distinguish which cells have a greater state of charge, therefore needing bleeding to balance their state of charge against other lower state of charge cells in the series battery stack.
So, pick your poison. Focusing solely on reduced cell cycle range to reduce the electrode expansion/contraction to reduce SEI damage to the neglect of maintaining state of charge balance is not a good approach to lengthening cell longevity. You need to do both.
When it comes to DIY'ers, there is a saying that 'cells don't die of old age, they are murdered first'. One overcharging mistake can severely damage cells. Excessive discharge current rates creates internal heating that increases the likelihood of electrode to metal foil current collector delamination increasing cell impedance. High charge current rates results in more electrons escaping into electrolyte during charging, creating more damage to electrolyte.
The wider the state of charge range the cells are cycled the more expansion and contraction of graphite negative electrode. The more expansion and contraction the more damage is done to the solid electrolyte interface protective layer. This protective layer is grown initially when a cell is new and is initially grown by manufacturer process after cells are fabricated. It is called the initial charge forming process.
The SEI layer is a thin coating over negative electrode graphite granules that retards electrons from escaping the electrode material into the electrolyte. When electrons enter electrolyte, it causes decomposition of electrolyte. Electrolyte decomp creates gases and tars as its byproducts. Tars clog the electrode pores that restricts the flow of lithium ions through cell, increasing cell impedance.
Fracturing and repair of the SEI layer is a normal part of cell aging process. Cracks are repaired during subsequent charge cycles. The fractures in SEI layer does allow some additional electrons to escape into electrolyte during charging and the repair action consumes a little of available free lithium ions that reduces cell capacity over repeat cell cycling. Again, part of normal aging process.
Maintaining a higher state of charge results in more electrons overcoming the SEI protective electrostatic barrier to escape into electrolyte resulting in additional damage to electrolyte. Overcharging, especially above 4.3v on a cell, allows a large amount of electrons to escape electrode creating a lot of damage to electrolyte. Most visible result is cell bloating, although the real damage is the tar clogging electrode pores.
Almost all BMS's restricts cell balancing to a cell voltage above 3.4v. This is point where cell is approaching full state of charge and has an accelerated rate in rise of cell voltage which makes it easier for BMS to distinguish which cells have a greater state of charge, therefore needing bleeding to balance their state of charge against other lower state of charge cells in the series battery stack.
So, pick your poison. Focusing solely on reduced cell cycle range to reduce the electrode expansion/contraction to reduce SEI damage to the neglect of maintaining state of charge balance is not a good approach to lengthening cell longevity. You need to do both.
When it comes to DIY'ers, there is a saying that 'cells don't die of old age, they are murdered first'. One overcharging mistake can severely damage cells. Excessive discharge current rates creates internal heating that increases the likelihood of electrode to metal foil current collector delamination increasing cell impedance. High charge current rates results in more electrons escaping into electrolyte during charging, creating more damage to electrolyte.
