Change in behaviour for Venus 3.40 prevents me balancing my batteries

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isavednokat asked 4 days ago

Change in behaviour for Venus 3.40 prevents me balancing my batteries

I have two almost identical systems with Multiplus II 10kVAs and 60kWh battery banks made up of 4 x 15kWh Cyclone batteries (made by MeritSun and register on the system as Pylontech, I think they use or clone their BMSes). I'm using the batteries' BMS over CAN, a Cerbo GX with ESS assistant, two Smart Solar RSs and each system has a legacy AC coupled grid tied inverter too.

I've just gone through a few days diving into Node Red on v3.34 (not relevant to the behaviour hence leaving this post in general questions) to automate setting the ESS mode to Keep Batteries Charged when the SoC gets close to 100% because it's the only way I can get the solar charge controllers to stay on and let the batteries balance after the first battery reaching 100% triggers a high voltage alarm - it's worked fine to keep it in that mode for a few minutes to let the batteries catch up to each other and all decide they're 100% but if I don't do that from time to time an ever increasing gap builds up between the SoC of the constituent batteries and this ends up having serious financial consequences on the effectiveness of the system as a whole, especially when running Optimised with BatteryLife which is my preferred setting.

So this behaviour and automation are working great on the one system but now when it comes time to make the other system follow along the Cerbo GX code version has gone up to 3.40. Now whether automating or manually I simply cannot override things at all. It gets to a high voltage warning (NOT alarm) and then forces Keep Batteries Charged off no matter what I do. So now the only way I can see to narrow the gap is to manually switch batteries on and off all day to let them catch up to each other which is simply not practical for me.

Is there anything else I can do to get the same result that doesn't involve forcing the version back to 3.34 and staying there indefinitely to avoid the new "fix"? How does one persuade the powers that be that this is a bug/needs to be changed back?

Lithium Battery Venus OS batterylife

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Alexandra ♦ commented · 4 days ago

How does a firmware update change current sharing on a battery bank?

What has probably changed is bank detection and information on a problem that has always been there now is being reported?

FYI just roll back. No point changing a working system.

Or lower system charge amps to give everything time to keep up.

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isavednokat Alexandra ♦ commented · 4 days ago

The change seems to be in how ESS state responds to a high voltage warning...whether that change was done specifically for the Pylontech case though I won't know until I find it in the codebase if I choose to go that far, just as for quite some time the DVCC implementation file had a special case that assumed all Pylontech batteries are 15 cell whereas mine are 16 cell...eventually a bit of logic was added to allow for that case but I had to use a hack I found here in the mean time...

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nickdb ♦♦ isavednokat commented · 4 days ago

As far as I am aware, the system does not do anything different after a BMS-generated high-voltage alarm. It still relies on the BMS and external control to manage the charge behaviour.

16 cell vs 15 was a different case.

I've had enough of those to realise it just needs time to resolve and it does no harm as the BMS protects the battery.

Extreme cases needed a short period of voltage limiting to assist balancing, the only exception being where the pack was far too small and was constantly being heavily discharged and spending insufficient time at top of charge to settle, or, an actual battery issue with an iffy cell.

As already advised, roll back, if you are certain it is an OS issue.

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Modifications Space

Node Red Space

Answer 1 · 2024-07-22T16:16:15Z

pwfarnell answered · 4 days ago

From the Cerbo GX manual

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

This may help to get the batteries to balance occasionally.

11.4.2. Limit managed battery charge voltage

Some batteries (like BYD and Pylontech) that come from the factory will take some time to settle in, and you may need to run them at a lower voltage for the first two weeks or so to help them balance.

This is what Limit managed battery charge voltage is designed for. Enabling this makes it possible to lower the maximum charge voltage until cells have balanced.

Do not use it for any other purpose as it may have unwanted side effects, for example, balancing can fail or not start at all if the charge voltage is set too low, causing the battery cells to become severely imbalanced over time. It is also not possible to set the value above the charge voltage limit (CVL) sent by the battery.

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isavednokat commented · 4 days ago

I have experimented with this in the past, although not for this specific case, but it tends to only make the situation worse...it might turn out to be a way to temporarily force the Keep Batteries Charged mode to keep going when I'm doing a manual balancing though...

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