I have three us5000 connected in parallel. They were all purchased at different intervals, latest one was October 2023. They have the following cycle count: 65, 205, 214. I've ran them both in PYL mode (easun/voltronic at 53.2V) and user (52V float 52.5V bulk). I have an issue with the latest module. There are no alarms/no red led lights and nothing bad in the log files that I could download with BatteryView.

Each day, once the voltage of the cells is above 3.45V (generally), there is a drift in between the highest voltage cell and the lowest voltage cell of about 0.14V. Highest would be 3.61V while the lowest would still be 3.47V. This happens gradually after 90% SOC. Below 3.4xV the cells show almost no imbalance.

The other two modules have a cell imbalance of 0.02V generally and it's maintained, irrespective of SOC.

Also the other two modules reach 100% faster than the 1st module, which stays at 98% for a while (20mins) in which the BMS temperature reaches 40C, while the cells remain at 27-28C(similar as the others). Then, the module would reach 100% as well and the cells would be 3.53-3.55V.

I know it's the balancer that does it's thing, but this happens every day and 100% SOC is maintained for 4-5h.

Pylontech support says to charge them individually to 53.2V OR to force charge them with the inverter and keep them at SOC for 5-8h. Well, the second option is done almost every single day in the past weeks. 

In the pictures below you can see the behavior in the reverse order (of the pictures). I am back to PYL mode to satisfy their requests of 53.2V. Before mid of last week I was running them at 52/52.5V in order to not have one cell go above 3.6V. 

Looking at individual cells with batteryview, it seems that it's not one cell that is too high or another too low, rather it's split in two groups.

Please advise. The seller tells me that if Pylontech support will not say it's an issue or if there is no red led or alarm, they will not do anything about it.

 

 

 

I would say it all looks pretty normal , it can take many cycles for that lower cells to come up to the level of the others. When you have batteries of different ages the stack will almost always behave like this in my experience. Don't charge to lower than 53,2 as this will hinder the balancing speed and process. 

Thank you. On this forum I've read that pylontech balancing starts at 3.45V, that's 51.75V. And anyway above that value there's not much capacity in Lifepo4 anyways, I thought to not stress the cells to much especially with the tendency of that cell to overshoot 3.6V. 

I have the same phenomena at 52.5V total voltage, so the balancing happens at that value anyway, and I guess there is no way to speed the balancing process by going higher voltage ... 

1 hour ago, onobeka said:

Thank you. On this forum I've read that pylontech balancing starts at 3.45V, that's 51.75V. And anyway above that value there's not much capacity in Lifepo4 anyways, I thought to not stress the cells to much especially with the tendency of that cell to overshoot 3.6V. 

I have the same phenomena at 52.5V total voltage, so the balancing happens at that value anyway, and I guess there is no way to speed the balancing process by going higher voltage ... 

Yes they do start balancing at 3,45V  but if you don't go higher with the mixed age battery packs they will tend to get unbalanced in my experience. Think of it this way , the balancing is only around 100mA+- in most of the commercial BMS's that means that the balancer has to do much more work at 3,45V than at 3,55V to get the pack balanced as 3,55V is at a much steeper part of the charging curve.

Much more work probably means much longer work, that’s true. Yet, since lifepo4 cells are flat voltage curve energy storage, extreme ends are sensitive. I agree that leaving them to go 53.2V might solve my claimed issue in a few weeks/days, but what if it does not? Will I run them for a year in this behavior, where one cell (or few) are exposed daily to over 3.6V? That might be permanent damage.

You can be sure what voltage your battery starts balancing at by using a terminal software like putty OR the console window in Batteryview (with Admin login of course) and type "config" at the command line.

This will show all the current settings in your battery.

BTW what version of Batteryview do you have?

Hi @onobeka,

I notice on your SA reports the "Max Charge & Discharge" rate is reported as 100A both ways.!

Just want to check, is that an actual measured number, of something you have configured on your inverter. I use SA as well, and mine doesn't show those values (both latest s/w and beta versions are the latest on my systems. Maybe just for Pylontech, as I have different batteries. Not sure why SA doesn't display those (incl Battery firmware version), as I'm sure it all get's transmitted to SA (just guessing)

If those values are measured, then I recon you are stressing those batts too much. My rule of thumb is 20A charge per 5 kWh battery, and the pack should discharge at the max that the inverter can handle when in Loadshed mode. 

I hope that 140 mV is not too big a delta to worry about, and hopefully is not an indication of a cell breaking down prem.

Just monitor regularly, even with Battery View, and then you'll know exactly which cell it giving problems, and try and replace that cell (before is expires!)

I would go back to Pylontech. You've done as they said and it's not resolved.

Keeping it floating at a high voltage for hours should have resolved it. None of mine require hours of balancing and as you say the ambient temp rise shows when they are actually balancing. (Bad design but useful)!!

Their is something wrong with that battery.

Had a similar issue with the sudden increase in "Ambient Temperature" above 90% SOC compared to the rest of my batteries. Firmware update didn't fix the issue. Subsequent BMS replacement also had no effect. Pylontech then replaced the battery.

1 hour ago, JKKM said:

Had a similar issue with the sudden increase in "Ambient Temperature" above 90% SOC compared to the rest of my batteries. Firmware update didn't fix the issue. Subsequent BMS replacement also had no effect. Pylontech then replaced the battery.

AFAIK all the new chip pylon batteries do this behavior, i have seen it many times with multiple people(my newest one does the same). So are you saying the battery does not have the same behavior now ? Do you know the hardware version of the BMS board? Pretty interesting that they would replace the battery for that if that's the case.

Battery BMS and inverters are complex systems, so I agree with @Tinbum

If you are concerned then you should go back to Pylontech.

HOWEVER, if you break down these complex systems into basic principles of operation then they seem not so complex, so lets try and do that.

The balance current of the battery is very small in comparison to the charge current, therfore, lets allow for balancing to take place when the charge current is also small. This will happen when the charge voltage and battery voltage are almost equal.

So set charge voltage to 52.5V ( 52.5 / 15 = 3.5V per cell...SAFE VALUE!!!) and if balance starts at 3.45V then delta V is only 0.05V.

Now the charge current will be small enough for the balance current to make a difference and cell voltage will be within safe limits for hours of balancing per day until battery cells are equalized.

This will take days because balance current is small.

As I said before you can know the balance start voltage with "config" command in console window and which cells are balancing with "bat" command

14 hours ago, Nexuss said:

AFAIK all the new chip pylon batteries do this behavior, i have seen it many times with multiple people(my newest one does the same). So are you saying the battery does not have the same behavior now ? Do you know the hardware version of the BMS board? Pretty interesting that they would replace the battery for that if that's the case.

Information from the battery that was exhibiting the behavior.

The new battery which does not have the issue. 

 

On 2024/03/07 at 7:47 AM, MeDat said:

You can be sure what voltage your battery starts balancing at by using a terminal software like putty OR the console window in Batteryview (with Admin login of course) and type "config" at the command line.

This will show all the current settings in your battery.

BTW what version of Batteryview do you have?

I have B2.0, B3.0.24 and B3.0.28. I will try the "config" command and report back.

On 2024/03/07 at 9:02 AM, Sidewinder said:

Hi @onobeka,

I notice on your SA reports the "Max Charge & Discharge" rate is reported as 100A both ways.!

Just want to check, is that an actual measured number, of something you have configured on your inverter. I use SA as well, and mine doesn't show those values (both latest s/w and beta versions are the latest on my systems. Maybe just for Pylontech, as I have different batteries. Not sure why SA doesn't display those (incl Battery firmware version), as I'm sure it all get's transmitted to SA (just guessing)

I did not set those values. There are the values for each module and also the cumulated values (first table, where it says Recommended ...).

The ones for the individual modules are always 100A/100A, that is the battery capacity in fact, us5000 is an 100Ah battery.

For the recommended values: I can see though that once the battery is above 90-95% (not always the same level), the max recommended charge current is reduced to 20/10/2A. Sometimes I can see that it's actually respected by the currents that go in the batteries, while other times, it's not. Also I think that is the current per battery, not the sum of the three modules. Also, I have charged the three batteries before with 140A (total), so even the 100A is not respected.

I start to believe that the BMS communication with the inverter (which only is in effect in PYL mode) does not control charging, it tells SOC and warnings/errors. In USE mode, the SOC is calculated in the inverter based on the voltage settings but it's not reflecting correctly the battery SOC (which I can see in SA).

When the batteries get full, the BMS is limiting the current, but it's not asking the inverter to limit the charge. This I consider normal and without this behavior one could not safely operate in USE mode. 

I also have a Victron charger connected to the battery bank, in which I can force an equalization mode on the battery. However, it's the BMS who will allow current to go in the cells or not, the SmartSolar charger can only output a certain voltage and sustain a certain maximum current for a period of time. So if the batteries refuse to balance pylontech should change something.

2 hours ago, onobeka said:

When the batteries get full, the BMS is limiting the current, but it's not asking the inverter to limit the charge. This I consider normal and without this behavior one could not safely operate in USE mode. 

I also have a Victron charger connected to the battery bank, in which I can force an equalization mode on the battery. However, it's the BMS who will allow current to go in the cells or not

 

 

No it doesn't work like that. The current is reducing just because the batteries are getting full. As they fill their resistance goes up so the current goes down.

The inverter charge current should be controlled by what the BMS is requesting- if not their is something wrong. In practice though,other than when the batteries are very empty, the current is limited by the battery chemistry not the BMS. I've never seen my current reduced because of a BMS setting- but it does depend on how big a battery bank you have. If you only had one of your batteries and not 3 you may see it.

When the battery is at 100% SOC then the BMS will request a charge current of 0A so the Victron will respect that. It may be an idea to set that up without communication to do a long charge as Pylontech recommend.

I still think your battery should not require cell balancing like this. It's new it should come balanced. Mine all have been fine from new.

Edited March 8, 20242 yr by Tinbum

6 hours ago, MeDat said:

Battery BMS and inverters are complex systems, so I agree with @Tinbum

If you are concerned then you should go back to Pylontech.

HOWEVER, if you break down these complex systems into basic principles of operation then they seem not so complex, so lets try and do that.

The balance current of the battery is very small in comparison to the charge current, therfore, lets allow for balancing to take place when the charge current is also small. This will happen when the charge voltage and battery voltage are almost equal.

So set charge voltage to 52.5V ( 52.5 / 15 = 3.5V per cell...SAFE VALUE!!!) and if balance starts at 3.45V then delta V is only 0.05V.

Now the charge current will be small enough for the balance current to make a difference and cell voltage will be within safe limits for hours of balancing per day until battery cells are equalized.

This will take days because balance current is small.

As I said before you can know the balance start voltage with "config" command in console window and which cells are balancing with "bat" command

Agree, but a new battery shouldn't require days to balance it should come balanced.

19 hours ago, Nexuss said:

AFAIK all the new chip pylon batteries do this behavior, i have seen it many times with multiple people(my newest one does the same).

This seems wrong. Have Pylontech also changed things in the factory that they don't put balanced cells in their 'new chip' batteries.

Do they eventually balance?

1 hour ago, Tinbum said:

This seems wrong. Have Pylontech also changed things in the factory that they don't put balanced cells in their 'new chip' batteries.

Do they eventually balance?

Yes they did all eventually balance ,this is with 4 of the new chip US3000C. It almost seems like the temp sensor is placed very close to the part of the BMS that does the balancing. But If you look at @JKKM post it seems like the hardware is the same but they gave him a downgraded software version from V2,2 to V2,1 and if that changed the behavior is probably not hardware related. 

4 hours ago, Nexuss said:

But If you look at @JKKM post it seems like the hardware is the same but they gave him a downgraded software version from V2,2 to V2,1 and if that changed the behavior is probably not hardware related. 

They replaced his battery though so it did look to be hardware related.

6 hours ago, Tinbum said:

No it doesn't work like that. The current is reducing just because the batteries are getting full. As they fill their resistance goes up so the current goes down.

The inverter charge current should be controlled by what the BMS is requesting- if not their is something wrong. In practice though,other than when the batteries are very empty, the current is limited by the battery chemistry not the BMS. I've never seen my current reduced because of a BMS setting- but it does depend on how big a battery bank you have. If you only had one of your batteries and not 3 you may see it.

When the battery is at 100% SOC then the BMS will request a charge current of 0A so the Victron will respect that. It may be an idea to set that up without communication to do a long charge as Pylontech recommend.

I still think your battery should not require cell balancing like this. It's new it should come balanced. Mine all have been fine from new.

I am not following. You’ve said the same thing as I did wrt. BMS limiting the current. Please read again.

Wrt. Victron equalization, it’s exactly as I’ve said. I can ask it to do equalization at 54V when the batteries are already at their claimed 100% at 53.2V. So, they will go to 54V which means the cells will still absorb some power, mainly voltage, not much current as they are lifepo4. This means that the BMS will still allow some form of charging above what it previously stopped. I know it is pointless charging as the curve is very steep. Maybe I need to force them to 54V for a longer period, like 8h to force equalization. 3.6V is still safe. I did not do this, except a very brief test.

8 minutes ago, onobeka said:

I am not following. You’ve said the same thing as I did wrt. BMS limiting the current. Please read again.

Wrt. Victron equalization, it’s exactly as I’ve said. I can ask it to do equalization at 54V when the batteries are already at their claimed 100% at 53.2V. So, they will go to 54V which means the cells will still absorb some power, mainly voltage, not much current as they are lifepo4. This means that the BMS will still allow some form of charging above what it previously stopped. I know it is pointless charging as the curve is very steep. Maybe I need to force them to 54V for a longer period, like 8h to force equalization. 3.6V is still safe. I did not do this, except a very brief test.

No I didn't say the same thing. You will see when the BMS is limiting as the inverter will be charging at the actual current that the BMS is requesting. ie If your BMS is saying a limit of 5A then the battery will be charging at 5A. If the battery is only charging at 2A then it is the battery chemistry that is doing the limiting not the BMS.

54v is too high.

Yes pylontech are asking you to do the equivalent of an equalization. Do it at something like 52.5v and do it for hours or days until the cells are no longer balancing.

Doing it for days while the battery is in service means, charging also from grid, right? I am only using OSO(only solar).

Or, otherwise disconnect the battery and use a DC charger. 
 

I see the current limiting every day when they go beyond 90-ish% SoC. I have no way to know what the BMS it’s saying other then what I see in SA or … if I woul connect a laptop to the battery, which I am doing at best once a few months if I get stressed again over this issue. 

That is why we try to help each other get pass those stressful moments.🙂

Pylontech datasheet recommends charging voltages between 52.5V and 53.5V. A charge voltage of 54V is outside the recommendations and the battery logs info in its history which pylontech often requires. We don't want them thinking you assisted in the battery's demise.

Lets look back at basic principles...

Current will flow if there is a potential difference (ie difference in voltage). The greater the voltage difference the greater the current flow.

If the charge voltage per cell is much higher than the balance voltage per cell then the current will be too large for the balance FETs to handle (eg. a 100mA balance current cannot win against a 50A charge current).

So for good balancing to take place you need two things...

1) The battery needs to be outside the flat portion of the charge curve

2) A low charge current so that the balance FETs can do their work

All this will happen automatically once you set the appropriate charge voltage (ie between 50mV to 100mV above the balance start voltage per cell  x 15) then just relax and watch science do its thing.

You don't need to use the grid solar only is just fine.

 

That’s what happened since the moment I got the new battery in October 23 and that is what is happening now. The winter was pretty dark, so there was not much chance of charging. Since february the battery is at 100% daily at noon with 4-5h of floating at high voltage, either 52V like before (use mode) or 53.2V like the last two weeks in pyl mode. 
Yes, some balancing takes place, but it seems to be brief and the next day the event of cells drifting is present again and again. Some cells in the first module will see every single day for 15-30min voltages of 3.62V while the others will linger at 3.47V. After that period all cells will be in 3.55-3.53V for a total of 53.2V. During that period, the module temperature also rises to 40C from otherwise 25C.

This never happened for the other modules. However their cells will still be in 3.55-3.53V, no not perfectly balanced either.

Maybe the issue is misunderstood. My issue is with that voltage drift and high module temperature. This cannot be good if it happens every single day, right?

So, at the end of the day we can say that they are balanced if we accept that 0.02V differences means balanced.  

Then you say: keep them for hours or days at 52V float, yet charge only from solar. How could this work if the batteries will discharge over night?!? Maybe you mean to use the inverter is SUB mode (not SBU as currently) or to charge from the grid or to shut down the batteries ocer night.

I appreciate your intention to help. Thank you!