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Batter SOC Instant Drop 50 to 0

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Nonlin

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This happened to me back in March and I top balanced them to the point the JK BMS could no longer balance them.

Now again this happens, clearly I will balance again but is this par for the course or do I need to get a better BMS since this one can't balance while discharging leading to an inevitable imbalance? Or is it the batteries themselves? Or a config issue on the BMS?
 

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Disregarding the low cell #5, the average cell voltage of 3.06 V indicates the pack is probably below 50% SOC to begin with. Then when the low cell voltage protection is triggered the reading drops to 0 because there is effectively no usable capacity left. Is the pack capacity actually 304Ah? Probably not. See attached Discharge Curve chart.

Cell #5 looks like it may need to be replaced.

Could you post the balancing menu settings. Should be set to start balancing at 3.4V, Bal Current 2A, Cell Volt Deviation 0.010V or less.

What are your charging voltages and times? The balancing issue could be caused by too short of an absorption cycle which does not give the balancer enough time to do its job.
 

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Hmm.
Well, 49 volts on a 16s battery is empty.
Where are you getting SOC from?
Cell 5 obviously has an issue.
I charge to 55.6v, 60 minute absorption, float at 54v. Balance turn on at 3.475
To grid at 49v. Back to battery at 52v.
 
BentleyJ said:
Disregarding the low cell #5, the average cell voltage of 3.06 V indicates the pack is probably below 50% SOC to begin with. Then when the low cell voltage protection is triggered the reading drops to 0 because there is effectively no usable capacity left. Is the pack capacity actually 304Ah? Probably not. See attached Discharge Curve chart.

Cell #5 looks like it may need to be replaced.

Could you post the balancing menu settings. Should be set to start balancing at 3.4V, Bal Current 2A, Cell Volt Deviation 0.010V or less.

What are your charging voltages and times? The balancing issue could be caused by too short of an absorption cycle which does not give the balancer enough time to do its job.
Click to expand...
Here are my BMS settings.

I got these batteries from 18650batterystore claimed as Grade A.

What evidence would I need to provide to show that cell 5 is bad or perhaps even claim the battery is not what they are rated for?

They have a 1 year warranty and it hasn't been 1 year but again IDK how I would even make claim on the warranty?

These right here.

www.18650batterystore.com

EVE LF304 Grade A Cells - 3.2V LiFePO4 304Ah Battery

Buy high-quality EVE LF304 Grade A Cells, a 3.2V LiFePO4 304Ah Battery with flexible bus-bar, nuts and bolts included. Designed for longevity with 10+ years design life, 4,000 cycles, and a rechargeable feature. Get the full excel report by request.
www.18650batterystore.com www.18650batterystore.com
 

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Battery needs to be fully charged to 56.8V (3.55V per cell) then float charged and balanced until a screen shot of the cell voltages shows they are within 0.010V. Then a discharge capacity test can be done. Ideally with a 3rd party shunt installed to have a second source of data.

Here is the 64 million $$ question. Would SS accept a failed discharge capacity test based only on the BMS data from their battery?
 
BentleyJ said:
Battery needs to be fully charged to 56.8V (3.55V per cell) then float charged and balanced until a screen shot of the cell voltages shows they are within 0.010V. Then a discharge capacity test can be done. Ideally with a 3rd party shunt installed to have a second source of data.

Here is the 64 million $$ question. Would SS accept a failed discharge capacity test based only on the BMS data from their battery?
Click to expand...
I incorrectly stated it was from SS, its 18650batterystore. I now notice their warranty makes mention of 1000+ pcs so IDK if my less than that is even valid.

I don't know how these things work.

SO it really seems like bad battery vs incorrect BMS config or installation?
 
Partimewages said:
What method of top balance?
Click to expand...
Top balance was with the JK BMS active balancer, last time I did it I let it do it till it decided it could balance no more based on the threshold I had set. I've done no discharge test, I don't think I have the equipment to do that.
 
TomC4306 said:
Disagree.
I think the balance start voltage should be your target absorption voltage.
Any cell that goes above is balanced, cells below that are left to charge.
Click to expand...
Well at this point we are splitting hairs. Any high cell will very rapidly "run" up to 3.475V anyway and start balancing.
Nonlin said:
Top balance was with the JK BMS active balancer, last time I did it I let it do it till it decided it could balance no more based on the threshold I had set.
Click to expand...
Yes, correctly done
Nonlin said:
I've done no discharge test, I don't think I have the equipment to do that.
Click to expand...
Victron Smart Shunt isn't that expensive
 
I might contact them and say every 3 months
BentleyJ said:
Well at this point we are splitting hairs. Any high cell will very rapidly "run" up to 3.475V anyway and start balancing.

Yes, correctly done

Victron Smart Shunt isn't that expensive
Click to expand...
I can get that, balance like I did last time and then just run a load with the shunt to test?
This right here right? https://www.amazon.com/Victron-Energy-SmartShunt-Battery-Bluetooth/dp/B0856PHNLX?th=1

Then with the data I can go to 18650batterystore with evidence that something needs replacing?

I was going to call them today and just tell them every 3 months I have this issue.

You see nothing wrong with my setup/config for the JK BMS that would lead to this behavior?
 
Max Balance Current is set to 0.6A should be increased to the Full available 1A or 2A depending on the model of BMS you have.

I was kind of wondering how a battery from SS had a JK BMS in it. Makes a lot more sense the cells came from a different vendor.
 
BentleyJ said:
Partimewages said:
I'm thinking you need to parallel charge to 3.500 volts. All of your cells may not be full.
Click to expand...
BentleyJ said:
Max Balance Current is set to 0.6A should be increased to the Full available 1A or 2A depending on the model of BMS you have.

I was kind of wondering how a battery from SS had a JK BMS in it. Makes a lot more sense the cells came from a different vendor.
Click to expand...
Click to expand...
0.6 amps is the max for this JK BMS.

Regardless I have gotten it to balance within the limit set in the config for the BMS.

Why is it questionable that cell 5 has an issue? Clearly it is the only one under performing here right?
 
You could leave the pack in charged state and see if it eventually balances. Could take a long ass time though if that one cell is really out of balance. Those are big cells.
Otherwise you could speed that process by charging the pack up (so things are similar when you put the cell back), take out that cell individually and tank up with a bench charger to 3.5-3.6, put it back in the pack, then see where things settle when pack is drained/recharged. You wont be able to tell if that cell is bad unless you're at empty or full here.
 
utkvols said:
You could leave the pack in charged state and see if it eventually balances. Could take a long ass time though if that one cell is really out of balance. Those are big cells.
Otherwise you could speed that process by charging the pack up (so things are similar when you put the cell back), take out that cell individually and tank up with a bench charger to 3.5-3.6, put it back in the pack, then see where things settle when pack is drained/recharged. You wont be able to tell if that cell is bad unless you're at empty or full here.
Click to expand...
I mean I have top balanced before and now 3 months latter this is where I'm at.
 
If the resistance of that cell varies from the rest it will eventually fall out of sync with the rest of the pack (but the bms balancer should make that unnoticeable). You might want to check the qr code to see if that cell is from the same batch, but even if it isn't this shouldn't be happening. Something seems off. It sounds like it may need to be swapped out
 
utkvols said:
If the resistance of that cell varies from the rest it will eventually fall out of sync with the rest of the pack (but the bms balancer should make that unnoticeable). You might want to check the qr code to see if that cell is from the same batch, but even if it isn't this shouldn't be happening. Something seems off. It sounds like it may need to be swapped out
Click to expand...
One thing I've noticed with this BMS is that it won't really balance unless it is charging, SOC is like near 100% and there is no discharge.
Since I use this 24/7 it is discharging every day all the time, it never has time to balance.
Maybe I need to get a new BMS? Or is this how all BMS work basically?
 
I wouldn’t call that cell bad yet. You might just have a bad buss connection. I hope you are using the flexible buss bars and not the thick billet type. Some of those tend to be convex so you get two lines of contact instead of a large area. Remove the busses from both sides of the suspect cell(s) and inspect and lightly buff bright both contact surfaces and reassemble. Check torques on all fasteners.
 
Nonlin said:
Since I use this 24/7 it is discharging every day all the time, it never has time to balance.
Click to expand...
This is what the absorption time is for.
Charge to full (above 3.45 per cell) and hold that voltage for an hour or two.
The battery acts as a buffer for your solar so even while solar is adequate from time to time with spikes and load the battery will slightly discharge by an amp and then slightly recharge by an amp. Back and forth, up and down. Let this happen during the absorption phase and the balancer will do its job during this time.

This is a TOP balance.
Get all the cells nice and pretty and even from the top and they will maintain fairly decent balance down to slightly below 3.1 volts and then begin to diverge from one another.
Totally normal. I think you are discharging repeatedly too low in the state of charge curve thereby accentuating bottom imbalance.
 
TomC4306 said:
This is what the absorption time is for.
Charge to full (above 3.45 per cell) and hold that voltage for an hour or two.
The battery acts as a buffer for your solar so even while solar is adequate from time to time with spikes and load the battery will slightly discharge by an amp and then slightly recharge by an amp. Back and forth, up and down. Let this happen during the absorption phase and the balancer will do its job during this time.

This is a TOP balance.
Get all the cells nice and pretty and even from the top and they will maintain fairly decent balance down to slightly below 3.1 volts and then begin to diverge from one another.
Totally normal. I think you are discharging repeatedly too low in the state of charge curve thereby accentuating bottom imbalance.
Click to expand...
If 3.1 and below they start to get uneven, then I should configure the BMS for low voltage cut off at 3.1? Or maybe the inverter? The way its setup up right now I basically have it cut out / bottom at at like their rated min voltage of 2.5 ~ 2.651718898603389.png
 
Nonlin said:
Here are my BMS settings.

I got these batteries from 18650batterystore claimed as Grade A.

What evidence would I need to provide to show that cell 5 is bad or perhaps even claim the battery is not what they are rated for?

They have a 1 year warranty and it hasn't been 1 year but again IDK how I would even make claim on the warranty?

These right here.

www.18650batterystore.com

EVE LF304 Grade A Cells - 3.2V LiFePO4 304Ah Battery

Buy high-quality EVE LF304 Grade A Cells, a 3.2V LiFePO4 304Ah Battery with flexible bus-bar, nuts and bolts included. Designed for longevity with 10+ years design life, 4,000 cycles, and a rechargeable feature. Get the full excel report by request.
www.18650batterystore.com www.18650batterystore.com
Click to expand...
Always double check BMS voltage readings with a meter, you could just have a bad balance lead connection or bus bar.
 
Nonlin said:
If 3.1 and below they start to get uneven, then I should configure the BMS for low voltage cut off at 3.1? Or maybe the inverter? The way its setup up right now I basically have it cut out / bottom at at like their rated min voltage of 2.5 ~ 2.65View attachment 223350
Click to expand...
The BMS is your safety device not your operational device. Set up your inverter charger back to grid settings to avoid that low place. Ideally, the BMS never trips.
 
TomC4306 said:
The BMS is your safety device not your operational device. Set up your inverter charger back to grid settings to avoid that low place. Ideally, the BMS never trips.
Click to expand...
Haven't hooked my inverter up to draw from grid yet didn't see the point but this sounds like a good reason to.

Using a multimeter and the cells resistance matches the others. Check all the tightness on the bolts and they seem good as well.

Can share a pic tomorrow of the whole setup
 
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