Pylontech SoC staying at 89%, 50.5 V, balancing OK

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carlosg asked Nov 16, '23

Pylontech SoC staying at 89%, 50.5 V, balancing OK

Sorry yet another post on the issue since I do not find the solution.

I have a Multiplus II with a Pylontech US3000C that has been working OK for 3 months, the battery was charging to 100%

After 2 cloudy weeks the batteries could not be charged to 100%, they stayed with SoC between 50 and 80% with the battery life option enabled.

Last Sunday it was sunny but the the system behaves weird:

-SoC increased from ãround 60% to 89% in a normal way, but afterwards it is blocked. A couple of hours with the MMPTs inyecting around 1000watt did not increase the SoC over 89%. The voltage was slightly increasing to 50,5 and temperature from 21 to 23 deg. Min cell 3.330 and max 3.332, it seems to be balanced.

Still cloudy and I tried yesterday to charge the battery with the grid but it has the same effect, I inyected 1000watt during 1 hour but the 1 kwh only increased the Voltage till 50,8 (and back to 50.5V when the charging stops). Cells continue having a good balancing around 3,386 to 3.388V. Temperature increased from 21 to 26deg but not the voltage nor the SoC.

I read in another post that at 89% the balancing starts, but my cells seem to be balanced. Another suggestion is firmware ulgrade to v2.8, I will try to make the cable and load it.

I am quite puzzled. I was expecting that at least the voltage would raise to 51-52V, even if the SoC is not increased by the internal logic of the BMS. How can the battery absorve so much power apparently for nothing? The battery capacity is 3,5 Kwh, can it waste so much power for balancing or other BMS stuff without increasing at least the voltage? Or may be I have to try longer (4-8hr) with a lower current. What is the recommended current and time to cross the 89% barrier?

There are SoC-Voltage curves from other LIFEPO manufacturers.

https://www.jackery.com/blogs/knowledge/ultimate-guide-to-lifepo4-voltage-chart

They could explain that the voltage does not increase with the SoC during most of the charging, but if I am close to 89% I would expect more voltage variations. I can try to inyect more than 1 kwh to see if I cross the magic 89% barrier... but instead of saving energy with the battery I am wasting a lot

Thanks

Carlos

Pylontech

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Answer 1 · 2023-11-16T16:08:24Z

Alexandra answered · Nov 16, 2023 at 04:08 PM

@CarlosG

Check that the pylontec is the system battery monitor.

If you are charging slowly they won't really go out of balance.

SOC on lithium is not related to battery voltage the curve is too flat for that.

Don't mess with the battery FW that will void your warranty.

5

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carlosg commented · Nov 16, 2023 at 04:24 PM

Yes, pylontech is the system battery monitor

What do you mean with charging slowly? Normally it charges max with 20A (1000watt) in the solar peaks, that is accepted by pylontech.

Yes, SoC is not fully related to the Voltage, only at the ends

Normally updating the firmware is recommended by all the manufacturers, but OK, may be in this case not.

Thanks for the answer

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Alexandra ♦ carlosg commented · Nov 16, 2023 at 05:08 PM

A us3000c is 3552wh.

Yeah I see you are charging from grid there not solar. Only going on what I see.

If you have drawn to 60% and are charging up at 20A per hour (continuously); it will take over 2 hours to recharge. Closer to 2.4 hours at 20A continuously to return the full capacity of the battery to storage.

how long is it stating at the 89%? Maybe you have SOC drift.

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carlosg Alexandra ♦ commented · Nov 17, 2023 at 08:38 AM

I charge solar MPPT when available (unfortunatelly very cloudy the last weeks in my place in Germany), if not I (or the Multiplus to keep the battery life) charge from the grid .

It stays long at 89%, last Sunday the MPPT injected 2-3 hours from the Sun and afterwards I injected another 1 hr 20A (=1kwh) from the grid but it keeps the SoC at 89%, I only notice battery temperature increasing during the charge around 5 deg. Unfortunatelly no sunny days expected next week to see if it can be fully charged. I think that the Multiplus tries to charge it full once a week from the grid to keep the battery life.

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Alexandra ♦ carlosg commented · Nov 17, 2023 at 05:16 PM

52v ÷ 15 cells is 3.46v per cell.

Your cells are at 3.38v at 89% there is still alot of energy to return to the cells.

With the bad weather it makes sense just to keep the batteries charged. Keep an eye on them.

What size inverter do you have? Do you meet the min requirement for the inverter?

If you look at the charge voltage limit the battery is probably requesting almost 53.2v for charge.

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kevgermany ♦♦ Alexandra ♦ commented · Nov 18, 2023 at 10:42 AM

@CarlosG

To clarify. The graphs you posted above look like they show values for a 16 cell battery. As @Alexandra said, Pylontech 48V has 15 cells. So you'll get 15/16ths of the values in your graphs.

As I've been told and experienced, the Pylontech BMS will reduce the charge rate as the batteries become charged.

Your cells are pretty much in balance. If you're worried about the overhead of charging from grid at low rates, just leave it as is, but keep an eye on cell balance. If it goes out charge for longer from grid when there's insufficient solar.

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Answer 2 · 2023-11-17T17:17:40Z

Craig Robinson answered · Nov 17, 2023 at 05:17 PM

It could be temperature related as I have just setup 2 stacks of 3 pylon L2 and they are taking an age to get to 100% at a temp of 5-8 degree C the BMS will control the charge but if too cold it will just take ages be patient or put a heater in to warm the batteries up

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Answer 3 · 2023-11-18T13:11:44Z

Richard Norman answered · Nov 18, 2023 at 01:11 PM

I have 3000c stack and I see the same behaviour at times, given enough time they still go above 89% and will reach 100% they just sit at 89% for awhile and then rapidly shoit upto 90-95%

I wouldn't worry about it just a foible in the system and reporting related.

I first saw this many months ago and batteries continue to function fine.

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