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velociraptor asked

BUG in MP II Charger when Pylontech Battery is Connected? Batteries overcharging!

The Victron Pylontech guide https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom states:

When DVCC is enabled, the battery (via the CAN-bms) is responsible for the charge voltage. The Pylontech battery requests a charge voltage of 53.2V. We have however found that in practice this is too high.
The Pylontech battery has 15 cells in series, so 53.2V equates to 3.55V per cell. This is very highly charged and makes the system prone to go overvoltage.
It should also be noted that a LiFePO4 cell stores very little additional energy above 3.45V.
For this reason we opted to override the BMS and cap the voltage at 52.4V. This sacrifices almost none of the capacity and greatly improves the stability of the system.

This makes a lot of sense. However, by error I found out that it is not implemented that way. The clamping seems to be implemented the wrong way round!

When I configure the absorption voltage in VEConfigure to 54 V, then it will charge the battery up to 54V and receive overvoltage alarm or destroy the batteries. The clamping to 52.4V is NOT THERE!

However, if I configure the absorption voltage in VEConfigure to 52.0 V, then it will ignore the 52.0 V and charge to 52.4 V. So, in fact, the clamping is implemented the wrong way. If the user sets something BELOW 52.4, shouldn't the user values be obeyed?

In fact, the same guide cited above says that the user should set the absorption voltage to 52.0V (see table!) If you do that, it has zero effect! The MP II will still charge to 52.4V absorption voltage.

I think this is a bug. If not, what would be the rationale behind this behavior?

I'm not sure where to report this type of bug, if not here please advise.

System Info: MultiPlus II 3kVA 48V, Pylontech US2000, AC coupled PV on AC_OUT, no other Victron devices except the MultiPlus, no DC connected chargers. Firmware v2.64, 20210227...

Multiplus-IIPylontechbug report
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Jack Peters avatar image
Jack Peters answered ·

Are the batteries destroyed?


The rationale is to charge the batteries at a lower voltage in the situation that the BMS does not take over the charge settings (not connected or set up properly).

If you want to limit the charge voltage lower than what the BMS requests then use limit charge voltage setting in DVCC.

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velociraptor avatar image velociraptor commented ·

? Please explain, this does not make any sense to me. In fact, I think you are simply not right.

1. Why can you manually set a HIGHER voltage but not LOWER voltage? In both cases the BMS should take over the charge settings but you can manually set a too high value. The situation that you "charge the batteries at a lower voltage in the situation that the BMS does not take over" is not active here. In fact, it will happily charge at a too high voltage despite the BMS being present but it will not allow you to charge at a lower voltage.

2. Why is the behavior exactly the other way round as documented on the linked wiki page concerning the "clamp to 52.4"?

3. I cannot find any voltage related setting in my DVCC menu. What would be the name of that setting. There simply is none. There is no external charger connected, only the MP II itself. AFAIK the MP II charge voltage is set via VEConfigure. If there is a different way to set a lower voltage please let me know exactly where to find it.

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velociraptor answered ·

Pls see comment above as well.

My interpretation right now is:

- If BMS connected and BMS requests more than 52.4V, then it will clamp that request at 52.4V. This one is fine.

- If BMS connected and user sets voltage ABOVE 52.4V, then it will use user voltage no matter what the BMS requests and also will NOT clamp to 52.4V. Will happily go to 54V and fu** the batteries into overvoltage shutdown. This one is problematic. However, one could argue that the user should be able to override BMS values.

- If BMS connected and user sets voltage BELOW 52.4V, then the user value is ignored. Now that one I consider a bug. If, according to 2, we allow the user to be able to override the BMS, why would the user only be able to set higher voltages and not lower voltages? How would the user enforce a lower value at all? Why can the user only manually fu** a battery (too high voltage) but not manually save a battery?

To me the correct behavior would be like that: If user sets value below 52.4V, use user value. If user or BMS request a value above 52.4V, use 52.4V. (Alternatively: We might allow the voltage to go beyond 52.4V if the user sets a higher value and the BMS requests it but that is not how it's documented.)

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netrange avatar image
netrange answered ·

How much 2000er Polys and PV are connected to the Multi in your System ???

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velociraptor answered ·

There are 3x 2000 Pylontech (7.2 kWh, 48V). The PV power is AC coupled, max. about 1.2 kW. The transfer switch is in ON state all the time so the excess power is fed back. The ESS grid setpoint is set to 0 but excess AC is allowed to be fed into the grid. I am very certain that the PV does not influence the described behavior.

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shaneyake avatar image
shaneyake answered ·

Seems like you have something misconfigured or more likely you have a firmware version mismatch on the muti and GX. 2.64 is quite old for GX. Also update the multiplus 489 is the latest.


VE.Config should be set to the values in Chart 5.2
Absorption voltage : 52.0V
Float voltage : 51.0V

The DVCC values will not override the values in VE.Config or directly programmed into the MPPT.
DVCC can only command a lower value, this applies for both current and voltage.

How is your battery monitor setup? Is it correctly setup to BMS and is the multiplus battery monitor turned off? Older GX firmware does not force on DVCC and does not force off SVS.

If you have export excess enabled then the multiplus will add a few millivolts to the battery back in a feature called over-voltage feed in. This can force voltage to go from 52 to 52.4 but this is normal and okay. You can lower this if you want in the DVCC menu.

If the multiplus is outputting more voltage than you have programmed into VE.Config, then there is a problem with you AC PV setup. Some users have limited AC-IN current, this should not be done when running ESS. As the inverter will limit current by dumping power into batteries.

First things to do is update multiplus and GX firmware. Report back if that has fixed your problems.



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velociraptor avatar image velociraptor commented ·

Please see my newest answer

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velociraptor answered ·

Indeed after upgrading, there is a new DVCC setting that allows to limit the charge voltage!

I'll report back once I've tested everything but there is very little sun today so it might take some time.

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velociraptor answered ·

@shaneyake: VE.Config should be set to the values in Chart 5.2
Absorption voltage : 52.0V
Float voltage : 51.0V

==> I've done that (initially and again after firmware update)

How is your battery monitor setup? Is it correctly setup to BMS and is the multiplus battery monitor turned off?

==> Yes, MP II battery monitor is turned off (the ESS assistant enables it and I turn it off again after installing the assistant). The Battery reports correct SoC to the MPII.

I can confirm that the DVCC voltage set to 52.0V will take effect. Without the DVCC it will still charge to 52.4V even though the VEConfig has set 52.0V. I do not believe this is related to over-voltage because (1) I have no DC coupled PV and (2) with the same amount of AC PV power it immediately goes from 52.4 to 52.0 once I set the DVCC voltage limit.


If this is the expected behavior, it should be documented like that on the cited wiki page for MP + Pylontech. This page gives the impression that setting charge voltage to 52.0 will indeed work but it does not. Also, the wiki page does not suggest to use the DVCC limit.

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shaneyake avatar image shaneyake commented ·
You don't need to use DVCC limit. 52.4V is totally fine for pylontech batteries. What most people don't realize is that the batteries don't come balanced from the factory. You should just set system to keep batteries charged and lower current to 5A or less per module and leave it for 3 - 5 days. Packs will all balance and system will run happly up to 54V after that.
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shaneyake avatar image shaneyake commented ·

I agree that balancing should be made clearer in the wiki tho.

It is talked about in the section
"'High voltage' warning or alarm shown on battery status"

It does suggest using the DVCC limit.

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