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alexch avatar image
alexch asked

Low battery Sustain mode Li Ion

I've been using a Multiplus 5000 for a few months. Parallel to the grid, it charges a 20 KWH li ion (NOT Lifepo) battery from 17kwP solar.

Now that the days recently got darker and rainy, I have an increasing low battery problem. The MP5000 goes into sustain mode at 33% / 51.2V.

The voltage of my cells is in the range of 2.7 ... 4.2 V (2 parallel Blocks with each 15 cells, 60V if fully loaded). Everything in the ESS is configured so that discharge should take place until 43V.

So why does the MP5000 stop at 51.2? Which Option did i miss?

Multiplus-II
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7 Answers
kevgermany avatar image
kevgermany answered ·

Have you checked the voltage settings in VE config using a MK3 USB adapter?

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alexch avatar image
alexch answered ·

Of courses, That's what I mean when I wrote "ESS config".

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seb71 answered ·

Still, could you post screenshots with the Multiplus settings or upload the configuration file?

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alexch avatar image
alexch answered ·

ess.jpg

ess2.jpg

summary.jpg


These are my values.

Just saw in summary my cutoff voltages (pic 3). Thought that DC input low shutdown would configure the off-voltage for battery loading (pic 1 39V). i am wrong, right, and should lower the voltages in ESS Setup? Would 46 - 45- 44 - 43V be OK?

Cell range 2,7 - 4,2 V.


ess.jpg (104.2 KiB)
ess2.jpg (93.8 KiB)
summary.jpg (50.6 KiB)
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seb71 avatar image
seb71 answered ·

When using ESS, the battery voltages set in ESS Assistant are the ones used.


The battery voltages from Inverter tab are ignored (but those should still be set to correct values just in case you delete the ESS Assistant for some reason).


So, according to your settings, the inverter will shut down if the battery voltage drops under 52V when there is very little or no load. And at 50V, 49.2V or 48V at those increasingly higher loads (current draw).


Sustain voltage should be set higher than the highest Dynamic cut-off voltage.

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seb71 avatar image
seb71 answered ·

Would 46 - 45- 44 - 43V be OK?

Cell range 2,7 - 4,2 V.


Can you monitor or measure individual cell voltages?

If yes, monitor which is the voltage of the worst cell, at different current draws from battery and select the battery voltage minimum limits based on that.

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Alexandra avatar image
Alexandra answered ·

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/controlling-depth-of-discharge.html#UUID-6b8f380a-3e19-c040-9dad-673577d775d5

Basically the voltage dropped under the C rating voltage of you load and has stayed there, so the system sustain was triggered.

You will have to grid charge a bit (to get it out of sustainl and possibly adjust your ESS dynamic cut or values if you want to use more battery capacity before sustain is triggered again.

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seb71 avatar image seb71 commented ·
He got wrong voltages set.
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Alexandra avatar image Alexandra ♦ seb71 commented ·
Yeah. I saw that.

Alot of lithium manufacturers just have one voltage for all the c rates in ESS. Usually just above the low cut off.


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groningen avatar image groningen seb71 commented ·
@Seb71

If I may, can you elaborate on voltage set you mentioned. Just curious and for general knowledge.

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seb71 avatar image seb71 groningen commented ·

@Groningen

He set wrong voltages.

He thought that he set the low limit for battery voltage at 43V:

Everything in the ESS is configured so that discharge should take place until 43V.

When in fact the voltages for Dynamic cut-off limits he had (according to the ESS Assistant screenshot) were 52V - 50V - 49.2V - 48V.

With Sustain voltage set at 50V.

Completelly wrong.

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groningen avatar image groningen seb71 commented ·
@Seb71


Aaa, ok, clear. Thanks for the prompt reply.

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seb71 avatar image seb71 groningen commented ·
When you asked that question, I realized that my reply could have been interpreted as if I talk about a "set of voltages".
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