question

Leave the voltage at 52V but reduce the current and let it charge, it can take some hours to balance the cells.

Cell3 and Cell4 might be bad/lower capacity than the other cells. Especially for Cell3, the difference in voltage (compared with the voltage of the other cells) is very big.

Since you are off-grid, your options are limited. Ideally you would want to not use that battery (just keep it charging) until all cells gets balanced/equal voltage at the top (assuming they would eventually get to that point).

Contact Pylontech (or your seller) and see what they have to say regarding this big voltage difference between cells.

This is normal, and it will happen every time you add a new battery to the system. In 1-2 days this will disappear. Still, why in the BatteryView you see only one battery, if you have now 3 units connected?

I've just been through the cell balancing exercise with two Pylonthech UP2500 (24V) battery modules. A couple of variables to keep in mind.

- it would seem either the time between manufacture and commissioning or since the last charge has a large effect on the time it takes the cells to be in balance.

- The most difficult battery to balance took many days to balance.

Procedure

Charge the new battery at a low current like 1A with the voltage set to 3.55V per cell. Using Pylontech software BatteryView is useful but not necessary, using Cerbo GX data can be used to monitor max and min battery cell voltage (it at least worked for my battery be it in a label reversed state).

- If and when the battery then gets to the Alarm state when one cell has reached 3.6V it will be necessary to disconnect the charger and let the battery sit for say 30 minutes to allow the 3.6V of the highest cell voltage to settle lower below the alarm threshold.

- then start charging at a reduce the charge current to 100-200ma (experiment on the highest current you can get away with without reaching the 3.6V). I used a separate constant current and constant voltage power supply. Set the voltage to 3.6Volts per cell and adjust the current to 100-200ma to prevent the highest cell from reaching 3.6V while the weak cells catch up. The catchup time can be days.... The below graph is my process of cell balancing, as you can see an initial cell balancing occurred around event 53, then event 105 the battery entered into an alarm state and nothing much happened the weak cells were charged very slowly.

At Event 170 I reduced the charge current (100-200ma) sufficient to drop the maximum cell voltage below 3.6V, then the BMS seemed to go into action balancing the weak cells more rapidly than before. You know when the full balancing has been achieved when the LED indicators on the Pylonthech battery goes into idle (single flashing top green LED) after maintaining 3.55V per cell for about an hour.

The Pylonthech BMS seems to be advanced but the software is poor at balancing the cells if they are unbalanced beyond a certain state, resulting in a poor customer experience. If I was commissioning a set of batteries it may be very prudent to bench charge (as it seems it can take days) all the batteries before going to the site eliminating time-consuming commissioning.

I hope this helps anyone with this cell imbalance problem.

I'm giving it the gentlest charge I can using the Easysolar II. Charge current is set to a max of 1A, and the charge voltage as high as it will go without creating high voltage alarms from the recalcitrant cell 3. Currently I'm at 50.9 V, and am increasing the voltage in 0.1 V increments when the charge current falls close to zero. I'll give this a go, and if I don't get anywhere soon I'll take it up with the supplier and Pylontech. I'll keep everyone posted. Thanks for the support so far.

Good day,

I would like to join the question here to understand more precisely how the cell balancing works with the Pylontech.

The equalization takes place according to my information only if:

-> At least one cell has over 3.450V &

-> The cell difference within the battery is over 0,030V &

-> The battery is being charged &

-> The battery is not in error &

The balancer discharges the cells with 50mA.

So, my questions:

• If the charge current of the battery is only 100mA, this is split between all 15 cells and thus all cells receive only 6.66mA. Does the balancer still discharge the cells that have a difference greater than 30mV with 50mA? Or only with 6.66mA
• Is the charge current within the battery always distributed equal between the 15 cells?
• When the battery is almost full I have 3.527V at the cell with the highest voltage and 3.378V at the lowest in the battery, so a difference of 0.149V. Is this value OK?
• When the battery is almost empty (SOC 20%) I have 3.235V for the cell with the highest voltage and 3.120V for the lowest in the battery, so a difference of 0.115V. When the battery is then charged again 100% it goes into cell overvoltage fault.
• If the battery is discharged only to 30% or even higher I have no problems and the system runs perfectly.

What is your assessment? Does this have to do with an unbalanced battery or does the battery have an internal cell fault.

I am trying to balance the battery with 1A each. See if it brings something.

Thanks

Hello @tiego ,

according to my experience I would use a bench power supply and select voltage with 53,2V and max current 2A. When the battery is going to reach SOC 100% it will reduce the current on it's own by the BMS. BMS might even cause that it suspend charging and switch the battery to standby. Don't worry! Be happy! Keep it on 100% SOC for many hours.

It is important that the battery is reaching regularly 100% SOC. In this state it will do the balancing of the battery cells and it might take really very, very long. Days! When some of the cells causes HV alarms it is on you to decide how to go on. I had already some Pylontech which claimed for some time HV alarms and after several time to charge it to 100% SOC it had perfect balanced cells and no longer any alarms. My understanding is let the BMS do it's job.

Nevertheless it might be that some of the cells are faulty, than there will be no way to balance them. Without knowing details and the history of the battery it is only guessing. Ask your supplier or Pylontech for help!

Servus - DayAndNight

Tiego, compared to the charging behaviour of my Pylons your cell values sound unbalanced. With current ESS mode your Pylons should get charged by the MP2 up to 52,8 V (formerly it was 52,4 V) and get balanced at that Voltage. My cells don't differ more than 50 mV at any charging state, at 52,8 V they differ around 30 mV, not much more or also less.

I would recommend you balance your Pylons fully charged at 52,8 V for some hours.

thank you all for the answers,

can I use a normal lab power supply (Amazon like) for charging or is there a charger from Victron over which I can charge the batteries from 230V AC without the risk of something going up in flames?

So I charge the batteries with the inverter to SOC 100%, then I remove them and charge them with 52.8 V or 53.2V with 1-2A with the lab power supply for a few hours?