question

Josep morancho avatar image
Josep morancho asked

Pylontech stays at 91% charge

I have seen a similar issue in another thread 6 month ago but without a clear reason/solution. Perhaps now the issue is more known and already solved

I installed 5 days ago an off-grid system composed by 2 x pylontech US5000, smartsolar 250/85, cerbo gx, multiplus II 48/5000/70-50 and a 3000w solar grid prviding 150V and 25A.

When i connected batteries to the off-grid system they were at 49% charge and they reached 100% in few hours.

2 days later theymoved down to 89% as it was a raining day and solar panels did not produce power.

After that the batteries stay at 91% charge. SmsrtSolar only produce the energy required to feed the load. Load is quite low as I was testing system before connecting high loads.

Firmware versions in smartsolar, charger and multiplus are the latest one.

Why does the charge percentage stay at 91% if load is very low and there is enough PV power to increase batteries charge?

DVCC is enabled, charge current limit has not been reached and there is not voltage oberload alarms.

Thanks

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1 Answer
Thomas avatar image
Thomas answered ·

Hi Josep,

try to increase the "Maximum charge voltage" in the DVCC Menu. Normaly the voltage is limited by the Pylontech via CAN-BMS and as you can see in the Parameters-Menu the BMS tells the GX the maximum is 53.2 V.

If the value in the DVCC-Menu is lower then that value will be used as the maximum voltage.

Best regards

Thomas

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nickdb avatar image nickdb ♦♦ commented ·

Max charge voltage is only meant for dealing with cell imbalances on new/recently added batteries. It is not supported to use it on an ongoing basis.

This is also documented in the recently updated DVCC guide:

https://www.victronenergy.com/media/pg/Cerbo_GX/en/dvcc---distributed-voltage-and-current-control.html

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Thomas avatar image Thomas nickdb ♦♦ commented ·

I have an installation with a Multiplus 2 GX and Pylontech. If the maximum charge voltage is only 52.3 V the batteries won't get to 100% charge.

And additionally the Pylontech limits the voltage by its own BMS.

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nickdb avatar image nickdb ♦♦ Thomas commented ·
Exactly, which is why it should not be set unless you are specifically dealing with a balancing issue, and when resolved, it should be disabled.

Even at the BMS CVL, pylons may not hit 100%, especially when new - something also documented in the victron setup guide.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

This is not useful for Pylontech.

The DVCC code contains "quirks" for a few of the batteries (incl. LG, BYD, Pylontech). The quirk for Pylontech applies a hard upper limit of 52.4V no matter what the setting in this menu is.

The code documentation shares the following:

Quirk for Pylontech. Make a bit of room at the top. Pylontech says that at 51.8V the battery is 95% full, and that balancing starts at 90%.

53.2V is normally considered 100% full, and 54V raises an alarm. By running the battery at 52.4V it will be 99%-100% full, balancing should be active, and we should avoid high voltage alarms.

Identify 24-V batteries by the lower charge voltage, and do the same
thing with an 8-to-15 cell ratio, +-3.48V per cell.

Use 3.48V per cell plus a little, 52.4V for 48V batteries.
Use 3.46V per cell plus a little, 27.8V for 24V batteries testing shows that's 100% SOC.
That leaves 1.6V margin for 48V batteries and 1.0V for 24V.

See https://github.com/victronenergy/venus/issues/536

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Josep morancho avatar image Josep morancho Warwick Bruce Chapman commented ·

I stopped battery charge for a couple of days and charge level decreased until 80%. Yesterday night i disabled "Maximum charge voltage" as requested and enabled again smart solar charger. After few hours battery charge level reached 91% and stopped there. BMS is not allowing more charge as pv grid still have sun power.

I see that cells are a little bit unbalanced. Highest 3.472 and lowest 3.489

Temperature is constant at 9 degrees at day and night

Batteries are new as they were installed just 1 ago

I read in this an other threads that this use to happen when:

1- batteries are new. The need time to stabilize cells

2- temperarure is below 10 degress and below 10 degrees this pylontech BMS apply a restrictive charging algorithm and do not allow to reach 100%

3- cells are unbalanced and then "Maximum charge voltage" change has to be apply


In my case the 3 possible reasons happen.


What should i do? Do nothing and wait some weeks to allow the battery to balance the cells by itself as they are new o act by changing Maximum charge voltage"?

Temperature will not increase at least during the following 4 months and perhaps will reduce few degrees more.

Thanks



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nickdb avatar image nickdb ♦♦ Josep morancho commented ·
If you had grid you would leave them on keep batteries charged for a few days, off grid is a bit more challenging. They really just need time to balance.
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Josep morancho avatar image Josep morancho nickdb ♦♦ commented ·

There is not grid. It is an isolated mountain house. I will have to be patient then. Thanks

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Josep morancho avatar image Josep morancho nickdb ♦♦ commented ·

d0f74583-c44d-4a45-9d8a-fe8200c0861e.jpeg3 days after connecting again smartsolar battery chsrger and dissabling "Maximum charge voltage" parameter as recommended, the batteries SOC moved from quickly from 91% to 97% quickly. Tenperature keep stable at 9 degrees and max and min voltage cell seems to be the same than previous years. Load has kept also constant at very low level all day.


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nickdb avatar image nickdb ♦♦ Josep morancho commented ·
@Josep morancho glad you’re making progress. It will get there. We’ve all experienced the frustration of a pack that just won’t get to 100%.
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Josep morancho avatar image Josep morancho nickdb ♦♦ commented ·

Very strange behaviour. Yesterday, after reaching 97% the day before and moving down to 91% at night, the SOC stayed at 91% all day and decreased to 86% during the night. Early morning today, SOC moved quickly from 86% to 91% and stayed there almost all the day but 1hour before sunset jump to 100% without any apparent reason as the day has not been cloudy and temperature and load have been constant all the day.

Today the cell voltage behaviour has also followed previous days behaviour. See all grahs attached. In the SOC graph, white circle is the evolution 2 days ago, yellow circle yesterday and red circle today. Only BMS charge and discharge limits shows today something diferent.

Highlight that previous increase from 91% to 97% was also done late in the afternoon close to sunset.

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