Differences in battery charging and discharging rates

[drackman]

Hi i have 3 of the exact same LiPo batteries from GoKwh

They work fine and have been connected with the original cables they came in

But one of the batteries is charging or discharging at faster rates providing or getting higher Amps

Any ideas why ?

A further update on this strange situation - when the inverter has reached the desired levels of SOC for the battery bank is stops charging lets say at 75% . But i get a very strange behaviour where Bat 2 keeps discharging and it then charges Bat 1 and 3 by keeping the average charge at lets say 75% to the point that bat 1 and 3 are at 100% and Bat 2 at 25%

Any ideas

These are GoKwh LiFePO4 batteries with a JK BMS - in parallel and linked via RS485 between them and to the Deye inverter by CAN from Bat 1

 

[AshleyL]

Post a picture on how you wires all three batteries.
Refer to this as reference :

 

[drackman]

They are in parallel and onto a bus bar

See below

 

[jgh]

a) you'll never get perfect current balance, nor SOC balance. But it will even out at full charge
b) note also the different temperatures

Don't obsess over it.

 

[drackman]

Yes I have noticed the temps as well -

Not obsessed about it but I am trying to operate between 80-20 and that battery gets a workout compared to the others

 

[jgh]

Wait, you said LiPo... Lithium Poly? Argh! Run!

Or do you mean LiFePO4 ? If so: a) ok, much safer b) there is zero point limiting yourself to only 60% of the available capacity. You paid for it; use it.

 

[drackman]

Its the later . LiFePO4 thanks

 

[AshleyL]

They are in parallel and onto a bus bar

See below

Can you expose these? Are you seriously putting two lugs together in one terminal?

At this stage, you should really take a look at Victron Wiring Unlimited guide book

 

[740GLE]

I wonder if the “stronger battery” is the single lug

 

[drackman]

No it not

 

[AshleyL]

No it not

So.....after putting the all three lugs properly based on Victron guide, how is the current distribution?

 

[drackman]

So.....after putting the all three lugs properly based on Victron guide, how is the current distribution?

I have ordered some additonal bus bars and rewired everything everything is same lenght etc.

Thank you for the guidance

Still the problem remains the middle battery pulls a lot more amps and either charges or discharges faster.

Here is the updated setup.

Any other ideas

 

[AshleyL]

I have ordered some additonal bus bars and rewired everything everything is same lenght etc.

Thank you for the guidance

Still the problem remains the middle battery pulls a lot more amps and either charges or discharges faster.

Here is the updated setup.

Any other ideas

Have you fully charged all three packs to 100% in a sense where there is little voltage deviation between all those cells in three packs?
*Meaning all cells are fully top balanced*

Since you mentioned all three are using JK-BMS, have you configure the BMS setting correctly? Just in case if you set the BMS to balance at wrong voltage level. You must not let the active balancer works below 3.45V.
Refer to https://off-grid-garage.com/my-settings/ section JK Inverter BMS (JK-PBxx Series)
I also would like to know your inverter charge voltage and GoKwh battery model
Tell more about the model of the JKBMS. If it is JK Inverter BMS (JK-PBxx Series), check the hardware revision and firmware version.

*Reason, old JKBMS firmware has nasty bug of causing the inverter in communication mode to prematurely "finished charging" without giving any time for the active balancer to work its top balancing magic*

*Try to charge the battery to full 55.2v (assuming if you have 16 cells battery pack) or 51.75v (if you have 15 cells battery pack), check if there is any large cell voltage deviation when the pack voltage is reaching 55.2v or 51.75v respectively.

 

[AshleyL]

??????What in the world???????????
Before that, take a look again on how you wire the battery packs again......
Pay attention to battery terminal locations where I highlighted.....



Should be:

 

[drackman]

Have you fully charged all three packs to 100% in a sense where there is little voltage deviation between all those cells in three packs?
*Meaning all cells are fully top balanced*

Since you mentioned all three are using JK-BMS, have you configure the BMS setting correctly? Just in case if you set the BMS to balance at wrong voltage level. You must not let the active balancer works below 3.45V.
Refer to https://off-grid-garage.com/my-settings/ section JK Inverter BMS (JK-PBxx Series)
I also would like to know your inverter charge voltage and GoKwh battery model
Tell more about the model of the JKBMS. If it is JK Inverter BMS (JK-PBxx Series), check the hardware revision and firmware version.

*Reason, old JKBMS firmware has nasty bug of causing the inverter in communication mode to prematurely "finished charging" without giving any time for the active balancer to work its top balancing magic*

*Try to charge the battery to full 55.2v (assuming if you have 16 cells battery pack) or 51.75v (if you have 15 cells battery pack), check if there is any large cell voltage deviation when the pack voltage is reaching 55.2v or 51.75v respectively.

Hi

Thanks for the suport

The cables have been corrected as indicated - on first glance no difference in the behaviour of the battery. Stills pulls and gives back more amps that the other two.

The active balancer is at 3.45V as i have seen in videos.

The batteries have been charged to 100% with stable voltage and balanced cells

The model of the BMS is JK_PB1A16S10P

The Inverter is a Deye SUN-12K-SG04LP3-EU

Not sure what you mean about the charge voltage of the inverter - it goes up as the batteries get charged , i use SOC to control the charging

The battery model is.

GoKWh 51.2V 100Ah 5kWh LiFePO4 Bluetooth Stack-Mounted Home Battery Storage​

Thank you

 

[AshleyL]

Hi

Thanks for the suport

The cables have been corrected as indicated - on first glance no difference in the behaviour of the battery. Stills pulls and gives back more amps that the other two.

The active balancer is at 3.45V as i have seen in videos.

The batteries have been charged to 100% with stable voltage and balanced cells

The model of the BMS is JK_PB1A16S10P

The Inverter is a Deye SUN-12K-SG04LP3-EU

Not sure what you mean about the charge voltage of the inverter - it goes up as the batteries get charged , i use SOC to control the charging

The battery model is.

GoKWh 51.2V 100Ah 5kWh LiFePO4 Bluetooth Stack-Mounted Home Battery Storage​

Thank you

For one, I doubt the accuracy of actual state of charge right now......because your BMS is currently on version 15.30.

Prior to version 15.35, if any of the cell voltage reach SOC100%Volt regardless of other cell, it will trigger the BMS to reset its SOC to 100% regardless. Next, the inaccurate JKBMS coulomb counting shunt will also cause the BMS to reset its SOC to 100% without the pack being actually charged to 100%.
Deye inverter will stop charging the moment JKBMS reports 100%.
You see the possible problem here? Premature charging termination and insufficient time for active balancing.

The latest and final firmware version for V15 hardware is 15.41.

I am suspecting your second battery pack might have higher true SOC% than the other two battery packs.

How do you ascertain all three battery pack have balanced cells?
Do you ever see the battery pack charged to 55.2V?
Pay attention to cell voltage when the pack voltage is nearing 55.0V - 55.2V.


edit:
Warning : Do not use SOC to control the charging if you are thinking to implement 20%-80% discharging/charging nonsense. It will never work with LiFePO4/LFP battery type. Lifepo4 battery has very flat voltage curve between 10%-95%. You must charge it to 100%, no way around it.



Recommendation = update the JKBMS firmware to latest version
Warning = don't flash the wrong firmware. There are hardware V14, V15 and V19. Each hardware revision has its own firmware.
Double Warning = flashing firmware can be very......dangerous?
Unfortunately, you don't have any choice either due to buggy JKBMS algorithm on early firmware revision.
I think you just missed out the "beta testing" period, you can find more here https://diysolarforum.com/threads/j...s-do-not-buy-warning-as-of-oct-12-2024.88573/
Page 1 to 62, recommend you to read slowly on issue and subsequent improvement on that thread, what a journey........

 

[MattiFin]

View attachment 331363

??????What in the world???????????
Before that, take a look again on how you wire the battery packs again......
Pay attention to battery terminal locations where I highlighted.....



Should be:
View attachment 331364

Your drawing can be a bit misleading. Wires should be same lenght.

My guess would be imbalanced battery packs.
3,4+3,4+3,6+3,6 pack would have same voltage but discharge different from 3,5+3,5+3,5+3,5v pack.

 

[AshleyL]

Your drawing can be a bit misleading. Wires should be same lenght.

My guess would be imbalanced battery packs.
3,4+3,4+3,6+3,6 pack would have same voltage but discharge different from 3,5+3,5+3,5+3,5v pack.

Eh......don't worry about it , he already mentioned he rewired everything and everything is same length......

He is using JKBMS V15.30 with the "buggy" SOC 100% reset algorithm. Not sure about his other two battery packs' BMS hardware revision and firmware.

Well, step by step I guess?
Proper busbar paralleling is completed on his part.
Next one = battery packs balancing time. This will involve firmware flashing and inverter+bms voltage calibration

 

[drackman]

Eh......don't worry about it , he already mentioned he rewired everything and everything is same length......

He is using JKBMS V15.30 with the "buggy" SOC 100% reset algorithm. Not sure about his other two battery packs' BMS hardware revision and firmware.

Well, step by step I guess?
Proper busbar paralleling is completed on his part.
Next one = battery packs balancing time. This will involve firmware flashing and inverter+bms voltage calibration

Thank you all for the support,

As Ashley said one step at a time.

PS I have checked all batteries are on the 15.30 firmware.

Will check the balancing again and report back

Bare with me as i travel a lot for work and time is limited

Again thank you for the guidance and support

 

[drackman]

I have set the inverter to control charging using Voltage

I have brought the batteries to a level and they seem to be balancing

Have a look

 

[AshleyL]

I have set the inverter to control charging using Voltage

I have brought the batteries to a level and they seem to be balancing

Have a look

Ouch, what a disaster. All three packs have out of whack cell voltage deviation. Almost all cells in each battery packs are not top balanced at all.
Remember, if you follow Andy's OffGridGarage settings, the situation should improved as you utilize those battery packs, never start active balancing below 3.45V.

For now, you will have to hold the voltage at 55.2v for the active balancing process to be completed until the cell voltage deviation (The Delta V in your screenshot) is below 20mV (preferably as low as possible, JKBMS can balance down to 3mV) on all three packs. Do note that this "holding the charge" is just a temporary procedure to ensure all cellls are properly top balanced. Might take long time depending on how out-of-balance those cells are........

Eventually, you will have to switch back to BMS to Inverter communication mode (SOC% charged to true 100%)......under the condition that you update the firmware to final and latest 15.41

Warning = updating the firmware will reset all the settings to default, so you will have to rekey/re-enter everything again. Just follow Andy's OffGridGarage settings, a tip, set the JKBMS setting from bottom to top.

 

[dustyPanels]

Is the middle battery pack warmer than the other two? When one of mine had sunlight on it, it discharged faster than the other two.

 

[drackman]

Well just a status update as i have been travelling

After all the balancing (down to 0.006v) and rewiring and updating the firmware etc the issue remains

The mid battery still pulls/gives twice the current as also verified indepentently by a clamp meter

Any more thoughts ?

 

[jgh]

At what state of charge? Have you measured over the full range?

 

[AshleyL]

Well just a status update as i have been travelling

After all the balancing (down to 0.006v) and rewiring and updating the firmware etc the issue remains

The mid battery still pulls/gives twice the current as also verified indepentently by a clamp meter

Any more thoughts ?

No more thought, other than the middle battery simply has lower internal resistance compared to other two.

You have done all you can with firmware update, top balancing and even positioning the busbar and connections correctly.