Good day to all. I would like to know if this is normal, when my battery reaches full SOC I see quite a big difference in the 16 cells voltage and one of them cell number 8 does not take full charge.   see attached dashboard. is this normal ? I don't want to name the battery make just yet. However I contacted the OEM and they recommend I bring the battery over for them to balance the cells. That worries me a bit as they don't want to tell me what the procedure is, I'm afraid they will charge the battery to a very high level thus reducing the life span of my battery.  Please your opinion will be highly appreciated.

I would charge the battery up to 100% daily for sure with LFP cells. You are worrying about the lifespan way too much. Charge up to 100% and see if that cell starts to sit at a higher voltage(this is what they will do anyway if you take it in) , if the voltage does not improve take it back to supplier .

I have observed my batteries bms work. It will start at 100amps then step down to 80 amps when the battery gets to 90%Soc it steps down to 40 amps which gets to 99%Soc very quickly. It will then keep going at 40 amps for another 20 to 30 minutes. Through all of that it never reads 100%Soc but it will go from 51volts to 52,4 volts and stop charging until the battery discharges below 95%Soc. 

What I can tell from all of that is that the bms does a top balance at the end which would be tedious to manually everyday.

This is why I always recommend using a bms cable with lifepo4 batteries. 

Edited February 4, 20223 yr by Buyeye

21 minutes ago, Nexuss said:

I would charge the battery up to 100% daily for sure with LFP cells. You are worrying about the lifespan way too much. Charge up to 100% and see if that cell starts to sit at a higher voltage(this is what they will do anyway if you take it in) , if the voltage does not improve take it back to supplier .

@Nexuss I do charge it to 100% every day and discharge to about 35 to 40% overnight. What you see in the in the dashboard in when the SOC is at 100% I can see that cell 8 voltage is getting lower and lower with time.

Also I float it at slightly lower that the recommended voltage recommended 54 v I do it at 53.7 V  Dashboard of charging and floating voltage.

 

Edited February 4, 20223 yr by Antonio de Sa

 

18 minutes ago, Buyeye said:

I have observed my batteries bms work. It will start at 100amps then step down to 80 amps when the battery gets to 90%Soc it steps down to 40 amps which gets to 99%Soc very quickly. It will then keep going at 40 amps for another 20 to 30 minutes. Through all of that it never reads 100%Soc but it will go from 51volts to 52,4 volts and stop charging until the battery discharges below 95%Soc. 

What I can tell from all of that is that the s does a top balance at the end which would be tedious to manually everyday.

This is why I always recommend using a bms cable with lifepo4 batteries. 

Yea i have also watched the bms work and do its wonderfull things. I normally reach 100% soc by about 10am ,the battery voltage will be around 52 volts , it will then slowly top balance the cells with 40-300watts of power till the voltage gets to 53,2,in this time another .4ish kwh goes into the batteries. So yea top balancing is super important to keep all the cells balanced to a tight voltage range.

11 minutes ago, Antonio de Sa said:

@Nexuss I do charge it to 100% every day and discharge to about 35 to 40% overnight. What you see in the in the dashboard in when the SOC is at 100% I can see that cell 8 voltage is getting lower and lower with time.

Also I float it at slightly lower that the recommended voltage recommended 54 v I do it at 53.7 V  Dashboard of charging and floating voltage.

Its getting lower with time because you are not charging the cells fully so it is struggling to balance the cells . 3,55 volts is a fully charged cell in my pylontech battery so im not sure why yours are so low. They should all be very close to that for a fully charged cell. edit* the battery should be kept at charging voltage for a few hours so it can fully top balance the cells,it takes a while .

Edited February 4, 20223 yr by Nexuss

2 minutes ago, Nexuss said:

 

Yea i have also watched the bms work and do its wonderfull things. I normally reach 100% soc by about 10am ,the battery voltage will be around 52 volts , it will then slowly top balance the cells with 40-300watts of power till the voltage gets to 53,2,in theis time another .4 kwh goes into the batteries. So yea top balancing is super important to keep all the cells balanced to a tight voltage range.

Its getting lower with time because you are not charging the cells fully so it is struggling to balance the cells . 3,55 volts is a fully charged cell in my pylontech battery so im not sure why yours are so low. They should all be very close to that for a fully charged cell. 

Most of then do reach +_ 3.52V when I get 100% SOC however, cell 8 it's always lower average about 3.4 V see dashboard

I think I must take it to the OEM.

13 minutes ago, Antonio de Sa said:

Most of then do reach +_ 3.52V when I get 100% SOC however, cell 8 it's always lower average about 3.4 V see dashboard

I think I must take it to the OEM.

 

Yea but they are not being kept at 3,52v long enough to balance ,they should be kept at that voltage for 2-3 hours atlast to try and sort that pack out , check then if that cell has come up in voltage , it takes a while as the bms only uses one or 2 amps to bring that cell up to the voltage of the rest,and if its much lower voltage it can take even longer. I would try this before taking it to the supplier.

21 minutes ago, Nexuss said:

 

Yea i have also watched the bms work and do its wonderfull things. I normally reach 100% soc by about 10am ,the battery voltage will be around 52 volts , it will then slowly top balance the cells with 40-300watts of power till the voltage gets to 53,2,in this time another .4ish kwh goes into the batteries. So yea top balancing is super important to keep all the cells balanced to a tight voltage range.

Its getting lower with time because you are not charging the cells fully so it is struggling to balance the cells . 3,55 volts is a fully charged cell in my pylontech battery so im not sure why yours are so low. They should all be very close to that for a fully charged cell. edit* the battery should be kept at charging voltage for a few hours so it can fully top balance the cells,it takes a while .

My battery is of different make, is a  LBSA and I have my settings as per OEM manual, don't want to exceed the settings, just now I will have a with the OEM warranty.

I will try tomorrow if the sun allows it to keep at full voltage for a few hour and see if the BMS does it work and balance all the individual cells.

The battery does get to full SOC and so far I'm happy with it's performance.

 

10 minutes ago, Antonio de Sa said:

My battery is of different make, is a  LBSA and I have my settings as per OEM manual, don't want to exceed the settings, just now I will have a with the OEM warranty.

I will try tomorrow if the sun allows it to keep at full voltage for a few hour and see if the BMS does it work and balance all the individual cells.

The battery does get to full SOC and so far I'm happy with it's performance.

 

Ya i know you have that battery from your previous posts haha. For 16 cells at 3,52 volts thats 56,32volts the battery has to reach in order to be considered full SOC. So you are definitely not going to 100% . edit * the pylon has 15 cells thats why it operates at lower voltage than your battery.

Edited February 4, 20223 yr by Nexuss

9 minutes ago, Nexuss said:

Ya i know you have that battery from your previous posts haha. For 16 cells at 3,52 volts thats 56,32volts the battery has to reach in order to be considered full SOC. So you are definitely not going to 100% . edit * the pylon has 15 cells thats why it operates at lower voltage than your battery.

I think LBSA cells are 3,2 V and the OEM manual says bulk charge 56 V and floating at 54 V, What I can see is once 100 % SOC  the BMS controls the individual cells at 3.2 V 

I will talk to LBSA on Monday.

 

Just now, Antonio de Sa said:

I think LBSA cells are 3,2 V and the OEM manual says bulk charge 56 V and floating at 54 V, What I can see is once 100 % SOC  the BMS controls the individual cells at 3.2 V 

I will talk to LBSA on Monday.

3.2 is nominal voltage . All LFP cells have the same voltage range. Bulk charging at 56v untill the battery stops taking current will fully charge the battery and balance the cells .

22 minutes ago, Nexuss said:

3.2 is nominal voltage . All LFP cells have the same voltage range. Bulk charging at 56v untill the battery stops taking current will fully charge the battery and balance the cells .

@Nexuss Tomorrow I will keep the battery at 56 V for an hour or so to see if it balances all the cells, once more thanks for the input.

1 minute ago, Antonio de Sa said:

@Nexuss Tomorrow I will keep the battery at 56 V for an hour or so to see if it balances all the cells, once more thanks for the input.

No problem man hope it helps , You will probably need longer than an hour if that cell is at a much lower SOC than the other(which is what i suspect). I would keep it there for 4-5 hours anyway or until you can see all the cells have reached 3,52. Then after a few days of use check and the cells should all be pretty much the same voltage in a very tight range. If that cell drops to being the lowest once again after fully charging every day to 56v its a faulty cell.

It looks like your cells differ too much in capacity for the weak balancing current on the Seplos BMS to balance them. My guess is that the OEM will test the battery, come to the same conclusion, swap the cell and return the battery to you. (Then the cycle might repeat)