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Upper/Lower Charging limits

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urbanhomesteader

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I have a 48V li-ion battery bank with 4 (8s2p) modules totaling 272Ah with a 2Kwh solar array - I do not currently have a BMS connected. I have a 12K Growatt Inverter and plan to expand my systems array to 3-4Kwh. Here are the battery specs:

Samsung

Height: 6.5 inches
Width: 19.25 inches
Length: 21.5 inches
Weight: 110 lbs
Mounting: Rack Mount
Nominal Capacity: 68 Ah
Nominal Voltage: 58.4 Volts
Voltage Range: 49.8-65.2 Volts
Thermal Monitoring: 8 Integrated Thermistors
Battery Monitoring: Integrated Board and Compatible Plugs
Voltage Range: 49.8-65.2 Volts
Connection Out: M8 Threaded Insert

I have a off-grid setup and rely exclusively on my solar for power.

thanks for the feedback
 
RCinFLA said:
Without a BMS you are destined to damage some cells. Most likely first failures will be some bloated overcharged cells.
Click to expand...
I will second this. It's not a question of if you will damage cells, but how long it will operate until you do damage cells.

I have a off-grid setup and rely exclusively on my solar for power.
Click to expand...

Not a good combination for a sole source of power.
 
RCinFLA said:
Without a BMS you are destined to damage some cells. Most likely first failures will be some bloated overcharged cells.
Click to expand...
I appreciate the feedback and have ordered a BMS. I am still interested in the recommended Upper and Lower charging limits for these batteries.
 
Optimum depends somewhat on your use case but recommend absorb (boost) to 3.55v per cell. Need to allow enough time at absorb voltage to allow balancing maintenance time as most BMS's do not start balancing until a cell reaches 3.4v per cell. A normal resistor dump balancer BMS only dumps 100 mA to 200 mA during balancing so need about two hours at each absorb level recharge voltage cycle for balancing,

If you fail to allow enough balancing time, the cells will diverge in state of charge over time. The usual result of this is less extractable capacity from battery because of limits of lowest state of charge cell and highest state of charge cell. Most common issue of insufficient balancing is BMS tripping off for cell overvoltage when a full absorb voltage recharge is attempted.

Greater discharge current draw by inverter and greater ambient temps increases rate of imbalance of cells.

Float charge level set to 3.35v to 3.40v per cell.

If using a SSC where there is a voltage level for reinitiating a full absorb cycle, set recycle to about 3.29v per cell to avoid running batteries up to absorb voltage too often which will increase their full charge stressing cycles. If you are pulling greater inverter load current the battery voltage with cabling voltage drop may dip causing more recharge cycles to be initiated and you may have to lower this reinitiate charge voltage.

No load rested cell voltage of 3.45v is fully charged cell. 3.295v no load rested voltage is 50% state of charge. 'Rested' time is no load or charge cell current for greater than 3 to 5 minutes. This allows time for cell to reach equilibrium. This rest time to equilibrium is longer at less than about 15% state of charge.

After fully charging, any cell voltage above 3.45v is surface capacitance charge that will bleed off quickly with 1 to 3 amps of load for less than 60 seconds after which the cell rested unloaded voltage will be 3.43v to 3.45v per cell. Reason why charging voltage is brought above 3.45v is to speed up charging. Do not charge above 3.65v per cell as this increases rate of cell electrolyte breakdown.
 
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It sounds like you have Lithium Ion, not Lithium Iron Phosphate cells, in which case your voltages are different from the vast majority of the cells here. Also, it's the "firey" kind of lithium, so a BMS is absolutely essential to prevent the loss of your home, I've seen many examples of LiIon batteries exploding into flames.

Do a TON of research to determine the exact chemistry you have, put the appropriate BMS (a LiFePO4 BMS will NOT work with Li Ion) on it and go from there.
 
Bvillebob said:
It sounds like you have Lithium Ion, not Lithium Iron Phosphate cells, in which case your voltages are different from the vast majority of the cells here. Also, it's the "firey" kind of lithium, so a BMS is absolutely essential to prevent the loss of your home, I've seen many examples of LiIon batteries exploding into flames.

Do a TON of research to determine the exact chemistry you have, put the appropriate BMS (a LiFePO4 BMS will NOT work with Li Ion) on it and go from there.
Click to expand...

Upon second look, I think you are correct. The 8S made me jump to conclusion they were LFP.

16 series 4.2v Li-Ion cell is getting a bit too high in voltage for upper limit on a 48v inverter.

65.2v/ 16 = 4.075v which is not a LFP cell, likely spec'd to less than full 4.2v charge to provide safety margin and greater battery longevity.

65.2v may be getting too high for many 48v inverters. If you charge to lower voltage you just get less capacity.

The Growatt 12k spec doesn't seem to even list their battery input voltage range limits. Fault code 03 is battery overvoltage but cannot find in manual what that voltage is. For reference their maximum lead acid battery equalization voltage setting is 60v so that is likely close to their maximum battery voltage limit. Growatt 12k high idle current will consume a 272 AH battery in about 5 days.
 
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MisterSandals said:
There seems to be confusion on your battery type. 272Ah sounds like Lishen LiFePO4 off hand.
Can you confirm what “li-ion” cells you have?
Which BMS did you order?
Click to expand...

Lithium Ion Rechargeable Samsung 18650 INR18650-33G 3150mAh 6.5A Pack of 39 Batteries​


jag35.com

Samsung SDI ESS Energy Storage Battery 16S 60 Volt - Used 13.2 kWh Rac

This Samsung SDI ESS Mega 3.3 backup battery has been decommissioned from a large ESS project with plenty of usable capacity left in them. This is a special purchase, and is limited to stock on hand. These packs are rated for 3.9kWh with a nominal rating of 3.3kWh. We have been testing them and...
jag35.com

.....googled the specs!
 
Picture appears to include BMS.

Nominal Voltage: 58.4 Volts / 16 = 3.65v / cell
Voltage Range: 49.8-65.2 Volts / 16 = 3.113v to 4.075v / cell

Still doesn't say what chemistry but its surely not LFP type.

I think biggest potential issue is max voltage level for 48v inverter.


Talk about scary conversion!!!. This guy is a mad man. When he pulls out the circular saw I thought you got to be kidding me. Lets spray all the metal chips into the battery unit guts.

Video is reversed. Notice direction of tightening screw and Husky box reading in background.

If it has original BMS, guess he leaves extra two cells connected to satisfy BMS. This is going to cause problems.
 
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RCinFLA said:
Optimum depends somewhat on your use case but recommend absorb (boost) to 3.55v per cell. Need to allow enough time at absorb voltage to allow balancing maintenance time as most BMS's do not start balancing until a cell reaches 3.4v per cell. A normal resistor dump balancer BMS only dumps 100 mA to 200 mA during balancing so need about two hours at each absorb level recharge voltage cycle for balancing,

If you fail to allow enough balancing time, the cells will diverge in state of charge over time. The usual result of this is less extractable capacity from battery because of limits of lowest state of charge cell and highest state of charge cell. Most common issue of insufficient balancing is BMS tripping off for cell overvoltage when a full absorb voltage recharge is attempted.

Greater discharge current draw by inverter and greater ambient temps increases rate of imbalance of cells.

Float charge level set to 3.35v to 3.40v per cell.

If using a SSC where there is a voltage level for reinitiating a full absorb cycle, set recycle to about 3.29v per cell to avoid running batteries up to absorb voltage too often which will increase their full charge stressing cycles. If you are pulling greater inverter load current the battery voltage with cabling voltage drop may dip causing more recharge cycles to be initiated and you may have to lower this reinitiate charge voltage.

No load rested cell voltage of 3.45v is fully charged cell. 3.295v no load rested voltage is 50% state of charge. 'Rested' time is no load or charge cell current for greater than 3 to 5 minutes. This allows time for cell to reach equilibrium. This rest time to equilibrium is longer at less than about 15% state of charge.

After fully charging, any cell voltage above 3.45v is surface capacitance charge that will bleed off quickly with 1 to 3 amps of load for less than 60 seconds after which the cell rested unloaded voltage will be 3.43v to 3.45v per cell. Reason why charging voltage is brought above 3.45v is to speed up charging. Do not charge above 3.65v per cell as this increases rate of cell electrolyte breakdown.
Click to expand...
Thank you for your input
 
sunshine said:

Lithium Ion Rechargeable Samsung 18650 INR18650-33G 3150mAh 6.5A Pack of 39 Batteries​


jag35.com

Samsung SDI ESS Energy Storage Battery 16S 60 Volt - Used 13.2 kWh Rac

This Samsung SDI ESS Mega 3.3 backup battery has been decommissioned from a large ESS project with plenty of usable capacity left in them. This is a special purchase, and is limited to stock on hand. These packs are rated for 3.9kWh with a nominal rating of 3.3kWh. We have been testing them and...
jag35.com

.....googled the specs!
Click to expand...
Batteries are Li-Ion chemistry
 
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