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nokiamade avatar image
nokiamade asked

No idle mode for Pylontech battery with Victron Multi?

Hello. I’ve installed Victron Multiplus2 47/5000/70-50 with Cerbo GX and Pylontech US5000 as grid backup solution for outages. Everything works pretty well with recommended settings (no ESS), except one thing which concerns a bit. After being recharged with current over 10A, the system at 100% SOC immediately starts to discharge at minute consumption rate of 5W and does so until battery voltage drops below 50V and SOC goes to 99%. Then Multi charges back Pylon to 100%, voltage up to 52.4V and cycle with discharge of 5W starts again. If initial recharge happens with 10A or less, the battery after topping to 100% stays in idle (all its leds go out and only stand by one blinks).


I tried to factory reset both Multi and Cerbo, switched off UPS and PowerAssist functions, but no changes to behavior. The only cure is to switch briefly Multi to Invertor only state and immediately back to On. It charges for a minute with small current and battery goes to Idle mode.


I suspected 5W was Cerbo consumption as I measured connecting it to battery alone. But then why Multi isn’t supplying it? And why does no discharge happen after charging with current lower than 10A? I also tried to supply Cerbo with another battery, but Pylon remained showing 5W discharge. Same time Multi reports voltage drop on battery but no consumption rate of 5W. Seems something drains it on DC side. Is it normal and I should leave battery cycling between 99 and 100%?

Pylontech
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nokiamade avatar image
nokiamade answered ·

@Alex Pescaru You solution works like a charm. Already 1 week system has been rock solid stable, Multi in absorption and Pylon in idle after every full charge. Highly appreciated!!!

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Alex Pescaru avatar image Alex Pescaru commented ·

Thank you for your appreciation and glad that I could help.

For reference, as the original advice was deleted, here is the solution: https://community.victronenergy.com/questions/309805/pylontech-15-cells-soc-behavior-and-overcharging-e.html

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Alexandra avatar image
Alexandra answered ·

@Nokiamade

Yes pylons do that even in an ESS system, they never stay at 100% sort of make a saw tooth graph on the VRM.

There are some schools of thought with lithium that should not be kept at a constant voltage. And dont forget it is the pylontec controlling its charge through DVCC anyway.

How have you programmed the inverter exactly?

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nokiamade avatar image nokiamade commented ·

Hi Alexandra. You are right, DVCC successfully recognized both Pylon/Multi and let Pylon drive the inverter. I only followed instructions on Victron site to limit Absorption voltage with means of VictronConnect and MK3 interface. I assume it can help if Cerbo disconnects for some reason. I remain curious why Pylon goes in idle when charged with 10A or less? Should I look into the battery settings and/or upgrade its firmware?

Charger tab

Parameter Setting
Battery type Lithium
Charge curve Fixed
Absorption voltage 52.0 V
Float voltage 51.0 V
Absorption time 1 Hr


VEConfigure Inverter Parameter Setting
DC input low shut-down 44V
DC input low restart 48V
DC input low pre-alarm* 48V
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Alexandra avatar image Alexandra ♦ nokiamade commented ·

Awesome, you used the guide. What program did you use to update and program.the inverter?

Did you check the lithium box on the charger tab? Set a storage mode at all?

They have poor low current detection. Or maybe the firmware doesn't recognise/compensate for it? Not sure which.

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nokiamade avatar image
nokiamade answered ·

I programmed with VictronConnect on Android and USB-MK3 interface. I selected lithium battery and storage option became unavailable, as I recall. Not sure what you meant on poor low current detection…

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Duivert NL avatar image
Duivert NL answered ·

If you want to use ESS you could always set it with “keep batterys charged” in ESS if you want to use them as backup when grid fails

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nokiamade avatar image
nokiamade answered ·

Do you think ESS setup can improve anything on my concern? Or VEconfig for setting up Multi? Or battery firmware update?

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nickdb avatar image
nickdb answered ·

Gents, if you want to suggest modifying a system. Be clear what you are proposing, the risks, that it is unsupported and rather use the modifications section.

Do not blindly accept advice given on the internet. Research the recommendation and understand who is giving it to you. Be careful.

Do not adjust things that you do not fully understand, nor that you can explain in detail.

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Alex Pescaru avatar image Alex Pescaru commented ·

What I've suggested is extracted from the Victron's source code.

It's a thing that is already implemented by Victron for Pylontech batteries.

For sure I can (now) explain it in detail, thing that, no offense, no one tried here: https://community.victronenergy.com/questions/269636/debugbatteryoperationallimits-usage.html

Small quote from a comment inside dvcc.py file/script, :

# Do the same for 24V batteries. The normal limit is C/2, so put the 
# limit to C/4. Note that this is just a nicety, the important part is
# to clip the charge voltage. That also fixes the sawtooth issue.
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nickdb avatar image nickdb ♦♦ Alex Pescaru commented ·

Deviation from the documented config will void your pylon warranty. So before flippantly advising people to make changes, be sure to advise of the potential consequences of a modification.

Hence why it is moved to a section that makes it clear that changes like this are unsupported and unsanctioned by manufacturers.

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Alex Pescaru avatar image Alex Pescaru nickdb ♦♦ commented ·

Please read that code and see full Victron opinion and how, in fact, Victron fixed some Pylontech quirks.

But you are right:

I am nobody and I may be far removed from the truth and anyone trying to do what I am suggesting is doing it at his/her own risk!


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nickdb avatar image
nickdb answered ·

Moved to modifications.

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nokiamade avatar image
nokiamade answered ·

Dears. First of all, thanks to Alex. I don’t think people who are far from programming would go for it anyway. What is still not clear, is official position of Victron manufacturer. Is root cause on side of Multi, Pylon or incompatibility between the two? And what is official recommendation - let the system fluctuate between 100 and 99% SOC forever with no risk of degradation?

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Alex Pescaru avatar image Alex Pescaru commented ·

Root cause is on nobody side.

Pylontech request CCL=0 when SOC=100%. Which Victron respects, by stopping its charger.

Problem is that when the charger stops, a small current is still drawn from batteries for various reasons.

A small part by the Multiplus own electronics, another part for when a sudden variation on load appears and Multiplus tries to supply it by consuming from battery and so on...

This will lead to a small decline in the battery voltage and SOC up until it hits 99% and then the Pylontech communicate a CCL different from 0 and the Multiplus feel the need to top it back until Pylontech says again CCL=0.

What is implemented inside Victron code is a way to keep the charger active and to supply a small current to Pylontech in order to compensate with the loses and to keep the float voltage steady. Also used when feedback is allowed, but this is not your case.

Pylontech says charge the battery with voltages between 52.5V to 53.5V. Your 51V float will be well below the Pylontech's specification and if someone will keep the battery permanently at a constant 51V voltage will not void Pylontech's warranty. In fact that bulk, absorption and float terms are relics from the age of flooded batteries. With LiFePO4 batteries only a voltage and a current (both specified by BMS) should be respected. Charge with no more than specified CCL in Constant Current mode until CVL. Then you can keep at CVL indefinitivelly in Constant Voltage mode. The rest is done by Kirchhoff laws and BMS.

Even if you keep the charger active with a current limit / offset, for example 5 amps, once the voltage at the battery / charger terminals reach the set float voltage, the current will reduce to almost 0 or at the level it's needed, compensating that small current draw that makes the SOC decline.

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nokiamade avatar image nokiamade Alex Pescaru commented ·
Thanks a lot, that was very clear)


Actually I got into Venus OS with root easily and it is not something what is new for me in linux based systems. Tomorrow will try your solution with close monitoring


Curious why recharge with current equal or lower than C20 changes the behavior..

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Alex Pescaru avatar image Alex Pescaru nokiamade commented ·

I've told you C20 because it's small enough to not cause you problems with the battery and for sure high enough to compensate the SOC decline.

The things are a little more complicated, because your hardware is also feedback / feed-in capable and therefore it constantly tries to sync with the grid waveform / frequency.

This also translate into small variations in ways it behaves when different loads and more of that load's variation.

But the initial advice from nick is sound, you need to learn more about the way it behaves and me to try to refrain more in giving advice.

Different way to be, different way to think, different way to act, different people...

LE:

If you know your way around a linux system, take a look at the /opt/victronenergy/dbus-systemcalc-py/delegates/dvcc.py to learn more about what we've talked.

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nickdb avatar image nickdb ♦♦ Alex Pescaru commented ·
Victron have been clear that using CCL=0 is not the way to restrict charging, as it cannot be honoured. Charge should be controlled by varying CVL. Unfortunately, batteries that use CCL=0 will never have the ideal results. My preferred batteries do vary CVL as well as CCL, which prevents unexpected behaviour. Ultimately though, this seems to be a bigger issue on undersized battery packs. My own pylons do not exhibit this behaviour.
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Alex Pescaru avatar image Alex Pescaru nickdb ♦♦ commented ·

This is why the Victron has implemented those Pylontech quirks in its code and "simulate" a CCL different from 0, with a mechanism similar to that CurrentOffset, like I've suggested to @Nokiamade

Your Pylons does not exibit that behavior probably because the load on that inverter/charger where the Pylons are connected is big enough and therefore there is a residual current that reach the Pylons and keep the voltage and SOC high enough. I am saying a residual current because the inverter and charger are sharing the same hardware and they are intrinsically linked.

Here's below an example from my system:

11.jpg


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11.jpg (157.0 KiB)
nokiamade avatar image nokiamade Alex Pescaru commented ·
I tried to increase pass through load on inverter, but it didn’t change the behavior in my case
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nokiamade avatar image nokiamade nickdb ♦♦ commented ·
Now I start suspecting if combination of 5kVa inverter with 5kW battery (recommended is 10kW) and manual control over AC loads can cause the issue. Doubts, doubts… But who knows, maybe two 5kW batteries would make a miracle..
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nickdb avatar image nickdb ♦♦ commented ·

Yes, the setup is certified by pylon and victron. Your warranty is based on this.

There is no issue with this minor variance of SOC.

Deviating from the config will void your warranty, so trust the manufacturer and use their setup. There are many, many installs with pylons. It works. You don't need to mess with it.

Degradation happens, that minor variation isn't a major factor beyond time and temperature, which have a greater impact.

On a properly sized system, variations shouldn't happen that often.

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nokiamade avatar image
nokiamade answered ·

Thanks, Nick.


Still I’d prefer @Alex Pescaru to contact me privately by email and explain the root cause and suggested curing. Otherwise we should be let discuss it here in full scope. Then everyone may decide on the risk, warnings to be considered

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Alex Pescaru avatar image Alex Pescaru commented ·

Hi @Nokiamade

I've tried to explain it above where you've asked for root cause.

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nickdb avatar image nickdb ♦♦ commented ·

That isn't something currently available on the community.

As a Victron community we have a responsibility to ensure members, especially new ones, get the full picture, and fully understand what they are trying to do. You are welcome to mod your system as you choose, it is at your own risk.

The setup docs are tried and tested, they are what your warranties are based on. if you choose to deviate, just understand you are trying to fix a problem that does not exist and ultimately will be unsupported.

Your query is best had with pylontech support.

Feel free to discuss modifying your setup, just be aware that you will be on your own if it doesn't work as expected.

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nokiamade avatar image
nokiamade answered ·

I saw Alex and appreciate your support/suggestion to adjust current offset. I’m just curious what physically consumes that 5W after recharge at 10A+ and why it doesn’t do at recharge below 10A for my 100A battery…

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