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udou asked

ESS / DVCC - Maximum Charge Voltage

Being new to this forum, I did not find an answer to my question / issue and hope somebody can help me.

TL;DR; What can I do to prevent a MP2 to discharge a fully charged battery when I lower the DVCC Maximum Charge Voltage?


I am having a pretty standard ESS setup with 1 MP2 and a Seplos Lifepo4 battery.

As I understood that DVCC doesn’t work perfectly with the Seplos BMS as the smart BMS (meaning the system always charges to DVCC Maximum Charge Voltage, but unfortunately never drops to a float voltage to ease battery degration).

So I worked a bit with NodeRed and have a pretty good looking setup, which automatically lowers the max charge voltage when the system reaches the bulk voltage. As described, immediately after lowering the max charge voltage, my MP2 discharges the battery till it reaches the new voltage instead of just lowering the voltage and let the LIFEPO4 batteries lower the cell voltage on its own.

Can anyone help me tweaking it so the MP2 doesn’t discharge my battery?


Many thanks in advance!


DVCC
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3 Answers
udou avatar image
udou answered ·

Btw all components on latest firmware except MP2 - there I have v497

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@UdoU have you checked out Andy's videos?

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udou avatar image udou klim8skeptic ♦ commented ·

Absolutely! I learned there about the issue I want to solve.


As described, combining DVCC and Seplos BMS yields into a system that keeps the battery on high voltage after full charge, aka no float voltage.


My solution works except for the fact that my MP2 discharges when lowering the DVCC Max Charge Voltage.

@Andy isn’t using an ESS at the moment at all to my knowledge

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dirk-s avatar image dirk-s udou commented ·

If you are working with node red: I would simply set the value "disable chatge" to 1. This stops the charger and the voltage of the batteries goes down from alone like expected.

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udou avatar image udou dirk-s commented ·

Thanks Dirk, will try today and let everyone know.

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udou avatar image udou dirk-s commented ·
Just tried to "disable charger" - but still no luck. After the battery is full absorbed and I lower the max charge voltage, the MultiPlus goes to "Discharge" and discharges max. Amp till the voltage lowers to the desired voltage.
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hominidae avatar image hominidae udou commented ·

besides that this is expected behaviour, did you try to limit/set the allowed Discharge Power in ESS settings to 0W at this situation?

Edit: the setting in ESS is called "limit inverter power", as opposed to "limit charge current" in DVCC settings

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nickdb avatar image
nickdb answered ·

If you force the system to drop the DC bus voltage beneath what it is actually charged to, it will naturally discharge, that is how electricity works.

Some batteries will set the CCL to 0.

Ultimately DVCC will do what the BMS tells it to do.

The max voltage parameter is not meant for ongoing use, it was implemented to help new batteries balance, and primarily for pylontechs which were more prone to issues on new installations.

If you want to change charging behaviour, the best place to do this is inside the BMS profile.

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udou avatar image
udou answered ·

Would the discharge also happen without DVCC when the MP2 goes from Absorption to Float? I don’t think so actually.


The BMS will not change any Voltages in any situation, therefore my attempt to mimic a float state for the charger

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Related Resources

DVCC chapter in GX manual