Hi all, if my Narada 48v 15s 100aH battery has mixed capacity cell's, what would the symptoms be? The bms shows the SOH as 100%, but capacity shows 53.8 ah. Looking at the cell voltages, there is a definite difference between some cells. At 100% charged, at +- 51.8 v, some cell's voltage is about 3.6v, while others is below 3.4v. As soon as I make the float voltage 51.9 or 51.2, 2 of the cell's go above 3.65v. I first thought the cell's is totally unbalanced, but now I think that there is a capacity difference between cell's. Both my batteries was installed in 2019, but only resently I got software where I can read the bms. I also noticed that the batteries was opened before as some of the screws is damaged. So the installer installed 2'nd hand batteries I believe! I am planning to strip the batteries to test all the cell's and top balance them next month. Has anybody got some idea's? I tried for about 3 weeks to keep batteries fully charged, but no change. I have 2 batteries connected in parallel, connected to 2 inverters connected in parallel. 

2 hours ago, Oros said:

Hi all, if my Narada 48v 15s 100aH battery has mixed capacity cell's, what would the symptoms be? The bms shows the SOH as 100%, but capacity shows 53.8 ah. Looking at the cell voltages, there is a definite difference between some cells. At 100% charged, at +- 51.8 v, some cell's voltage is about 3.6v, while others is below 3.4v. As soon as I make the float voltage 51.9 or 51.2, 2 of the cell's go above 3.65v. I first thought the cell's is totally unbalanced, but now I think that there is a capacity difference between cell's. Both my batteries was installed in 2019, but only resently I got software where I can read the bms. I also noticed that the batteries was opened before as some of the screws is damaged. So the installer installed 2'nd hand batteries I believe! I am planning to strip the batteries to test all the cell's and top balance them next month. Has anybody got some idea's? I tried for about 3 weeks to keep batteries fully charged, but no change. I have 2 batteries connected in parallel, connected to 2 inverters connected in parallel. 

If the BMS stats are correct these are not 100AH batteries, but I suspect that the stats are not correct and rather that your SOH is 56% on the one and 53% on the other.

When the batteries are at 100% SOC those voltage differences are expected and nothing to worry about as long as the cells are regularly balanced. 

 

 

4 hours ago, Oros said:

Hi all, if my Narada 48v 15s 100aH battery has mixed capacity cell's, what would the symptoms be? The bms shows the SOH as 100%, but capacity shows 53.8 ah. Looking at the cell voltages, there is a definite difference between some cells. At 100% charged, at +- 51.8 v, some cell's voltage is about 3.6v, while others is below 3.4v. As soon as I make the float voltage 51.9 or 51.2, 2 of the cell's go above 3.65v. I first thought the cell's is totally unbalanced, but now I think that there is a capacity difference between cell's. Both my batteries was installed in 2019, but only resently I got software where I can read the bms. I also noticed that the batteries was opened before as some of the screws is damaged. So the installer installed 2'nd hand batteries I believe! I am planning to strip the batteries to test all the cell's and top balance them next month. Has anybody got some idea's? I tried for about 3 weeks to keep batteries fully charged, but no change. I have 2 batteries connected in parallel, connected to 2 inverters connected in parallel. 

How can you have a reading of 3.323V yet the BMS gives the minimum value 3.543V for the lowest cell. 

3 hours ago, I84RiS said:

When the batteries are at 100% SOC those voltage differences are expected and nothing to worry about as long as the cells are regularly balanced. 

 

 

Really, i don't think so at all. They should only be mV different.

The problem is that ICC is the only software that I know of that can read the batteries bms. I think the capacity reading is correct, because the batteries does not last long. The only way to balance the cells is by stripping the batteries and connect 2 or 3 cells in parallel and charge them to 3.65v. Top balans. Then assemble them again. 

7 minutes ago, Oros said:

The problem is that ICC is the only software that I know of that can read the batteries bms. I think the capacity reading is correct, because the batteries does not last long. The only way to balance the cells is by stripping the batteries and connect 2 or 3 cells in parallel and charge them to 3.65v. Top balans. Then assemble them again. 

Thats what I'd do, but parallel all of them together.

First thing is to open it up. See if you can find a qr code that you can scan to show you the manufacturer and the capacity of the cells.  Also, noted by @Scorp007. There is something wrong with that readout.  Minimum voltage is higher than voltage of cell no2, and many other cells. Not sure what is going on there

7 hours ago, Tinbum said:

Thats what I'd do, but parallel all of them together.

Yep, planning to do that, only i'm going to do a few at a time as a big powersupply that can do 20 to 30 amps is scarce. 

7 hours ago, gimme_power said:

First thing is to open it up. See if you can find a qr code that you can scan to show you the manufacturer and the capacity of the cells.  Also, noted by @Scorp007. There is something wrong with that readout.  Minimum voltage is higher than voltage of cell no2, and many other cells. Not sure what is going on there

Yep, i think the only solution is to strip the batteries and the check all the cells and connections. As with the reading, I'm also thinking of later to replace the bms. The Narada bms is not user friendly!! But, ja, as soon as i strip them i'll know. I'm also thinking of removing the comms between the 2 batteries. As some cells on number 2 reaches 3.65, then charging on both stop. So no.1 does not fully charge. I first need to get another comms cable to be able to monitor both. 

12 hours ago, Scorp007 said:

How can you have a reading of 3.323V yet the BMS gives the minimum value 3.543V for the lowest cell. 

I keep seeing this with this ICM software, I think it is a problem with the display of the values, but I don't know if it affects the balancing or not. It's a little disconcerting that so many people use this software and there is still such a blatant error.

1 hour ago, Oros said:

Yep, i think the only solution is to strip the batteries and the check all the cells and connections. As with the reading, I'm also thinking of later to replace the bms. The Narada bms is not user friendly!! But, ja, as soon as i strip them i'll know. I'm also thinking of removing the comms between the 2 batteries. As some cells on number 2 reaches 3.65, then charging on both stop. So no.1 does not fully charge. I first need to get another comms cable to be able to monitor both. 

Have you tried to re-calibrate the BMS yet? This can usually be done by discharging the battery until the BMS low voltage cutoff (sets SOC to 0%) and then charge it back up to the overvoltage cutoff (sets SOC to 100%) and it will then calculate the capacity and SOH from how much charge it gets into the battery.

It is important to do this without comms to the inverter so the BMS doesn't stop the charging due to incorrect calibration. I would do one battery at a time, get them to 100% and then hook them both up in parallel again with comms.

2 hours ago, Oros said:

Yep, planning to do that, only i'm going to do a few at a time as a big powersupply that can do 20 to 30 amps is scarce. 

12V 40A PSU are common and cheap. Sort the cells by voltage and connect 1P4S, 2P4S, 3P4S or 4P4S. Check regular to prevent a low capacity cell from charging to a too high voltage while the other 3 are still low. This can save a lot of time for a bit of effort to supervise charging. 

These PSUs can charge to over 80% SOC and just do the last bit with an adjustable PSU before doing a balance with all the cells in parallel. Only for phosphate cells. 

Edited August 11, 20232 yr by Scorp007

1 hour ago, Scorp007 said:

These PSUs can charge to over 80% SOC and just do the last bit with an adjustable PSU before doing a balance with all the cells in parallel. Only for phosphate cells. 

These seem pretty decent, I have the same one from takealot. There is a little voltage regulator screw on the left of the terminals which can probably be used to increase the voltage to charge the cells to full. I've not tested how high it can go though.

1 minute ago, jumper said:

These seem pretty decent, I have the same one from takealot. There is a little voltage regulator screw on the left of the terminals which can probably be used to increase the voltage to charge the cells to full. I've not tested how high it can go though.

All the units we have and used daily only allow up to 13.8V which is a bit too low for full charge. It is a good safe level as 1 cell might be higher than the rest specially when working with used cells. 

We also use the 24V 20A version on a test bench. 

On 2023/08/10 at 10:04 PM, Tinbum said:

Really, i don't think so at all. They should only be mV different.

Once the balancing is completed then yes. While still charging you will see this very often.

If the differences are always only a few mV then why would there be something like cell balancing at all.

Maybe in the high quality EV batteries this can be expected where cells are meticulously matched to each other.

Edited August 12, 20232 yr by I84RiS

2 hours ago, I84RiS said:

Once the balancing is completed then yes. While still charging you will see this very often.

If the differences are always only a few mV then why would there be something like cell balancing at all.

Maybe in the high quality EV batteries this can be expected where cells are meticulously matched to each other.

Any Li battery requires a balancer and a BMS.

His battery has a balancer so cells should not be no more than mV apart as in ANY other battery.

Cells in any battery should be matched.

The reason for a manual balance is because either the cells are U/S or the balancer hasn't been able to supply enough current to keep the cells balanced. (eg undercharging or damaged cells).

Edited August 12, 20232 yr by Tinbum