question

Daniel avatar image
Daniel asked

Big voltage difference between Pylontech BMS and MultiPlus-II GX

Hi all,

ESS-system details are: MP-II GX 3000, Pylontech US2000C and 2 MPPT

Wiring and setup according to pylontech_phantom.

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

But currently it is not connected to grid because we wait for approval of grid company.


Issue is that MP-II and Pylon BMS are showing constantly different voltages as shown in dashboard

49.78V (BMS) vs. 52.36V (MP):
dashboard-voltagediff.jpg

Impact is that Multi doesn't allow the battery to be charged by MPPTs because it is sharing the wrong voltage with them, and 52.4V is the charge limit. For example 1 MPPT has:
mppt-wrong-voltage.jpgBut the battery does actually have only 49.78V

pylon-real-voltage.jpg


GX-system setup battery monitor is autoselected with Pylontech.

gx-system-setup-batterymonitor.jpg


I could not find any hint why this is happening. Does someone had similar results and what could be done to get Multi to use BMS voltage ?

Thanks in advance for any help.


Multiplus-IIPylontechgx device
dashboard-voltagediff.jpg (43.0 KiB)
mppt-wrong-voltage.jpg (37.1 KiB)
pylon-real-voltage.jpg (26.4 KiB)
gx-system-setup-batterymonitor.jpg (41.0 KiB)
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9 Answers
Alexandra avatar image
Alexandra answered ·

@Daniel

DVCC allows the Pylontec to control the system. So it does not matter what the multiplus is reading at this point.

Check the torque of the battery connection on the Multiplus.

Do the mppts wake up when you put a load on?

If not check the polarity panels of the mppts is correct

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checkit avatar image checkit commented ·
@Alexandra If the Multiplus voltage reading hits 52.4V, it stops charging. So it does matter what the Multiplus is reading. I know the Pylontech is in control, but the Multiplus overrules it when the the voltage limit is reached.
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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·
This is partly true. Pylontech has SVS forced off in DVCC. This means the BMS voltage is not used by the system but rather the voltage as read by the Multiplus. In this case the differential means the battery will be under charged.
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checkit avatar image
checkit answered ·

@Daniel @Alexandra I am seeing the same problem at two sites with Multiplus 2 5000 and managed batteries (Pylontech). The VE Bus voltage reading is around 2V higher than the BMS voltage reading. This results in the battery not charging properly, because when the Multiplus reaches 52.4V (upper voltage limit), it stops charging.

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nickdb avatar image nickdb ♦♦ commented ·
This is where a thermal camera comes in handy, it will show all the hotspots and which are hotter than the others.

Fuse holders can also be problematic some times, if the fuse isn't make perfect contact or arc'd at some point.

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Alexandra avatar image Alexandra ♦ commented ·
@CheckIT

Usually there is a high resistance connection to the battery when I have seen a 2v difference like that. So that is somewhere to start

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cedricr21 avatar image cedricr21 commented ·
Have you find the solution of your problem? Thanks
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checkit avatar image checkit cedricr21 commented ·

@cedricr21

Yes, I have found a solution. The local Victron service centre re-calibrated the Multiplus DC bus voltage to match that of the BMS and a multi-meter. They managed to do this by establishing a remote desktop connection to my laptop which was connected to the Multiplus with an MK3 interface. They ran a software app that allows you to enter a voltage to calibrate the VE Bus card inside the Multiplus.

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volker avatar image volker checkit commented ·

I got a similar problem. My system goes into Absobtion, because of a ~2V offset during charging.

Can you explain what App exactly is needed?
The VictronConnect v5.91 Windows ask for a passwort for changes. Is that why you need the Victron service centre?

best Volker

PS All Software is up to date, based on the VRM info.

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cedricr21 avatar image cedricr21 volker commented ·
Dns mon cas le multiplus ii était défaillant. Victron a effectué un rempypar un multiplus neuf
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Daniel avatar image
Daniel answered ·

Connections seam to be fine
mp2-connections.jpgMPPTs are waking up as far as voltage is dropping below 52.4V when loads are kicking in. Small loads are working, big ones aren't. Moreover, once there is no production any more, VE.Bus system is raising low battery alarms, with no loads at all. It's just own reading from MP-II that is swinging up and down.

vebus-voltage-drop.jpgBut Battery voltage actually didn't change.

1663791176957.png

Edit: the alarm from VE.Bus

1663791324834.png



mp2-connections.jpg (146.9 KiB)
vebus-voltage-drop.jpg (28.8 KiB)
1663791176957.png (13.0 KiB)
1663791324834.png (6.9 KiB)
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Alexandra avatar image Alexandra ♦ commented ·
@Daniel

It sounds like there is a problem between your battery and multiplus. (On the battery leads connection particularly.)

You need to check the positive and negative and any fusing or disconnects inbetween with a meter.

As well as if there is actual voltage coming out of the battery itself by shutting down the system and checking the battery disconnected from the inverter.

1 Like 1 ·
najab avatar image najab commented ·
I saw something similar with the voltage registered by the Multiplus jumping all over the place. It was a loose connection so I second the suggestion to double-check everything - back the screws/bolts off and tighten them back down again.
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Daniel avatar image
Daniel answered ·

Today again, sharp drop in voltage when mppts are shortly before the end of production:

vebus-voltage-drop2.jpg

as voltage goes down, mppts are trying to work against it

mppt-shortly-before-eod.jpg


vebus-voltage-drop2.jpg (49.4 KiB)
mppt-shortly-before-eod.jpg (46.5 KiB)
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Alexandra avatar image Alexandra ♦ commented ·

@Daniel

You need to check it with a digital multi meter at the Pylon battery terminals and at the inverter terminals and the mppt terminals. It will help diagnose what is happening.

If you switch the system to keep batteries charged does it help or change anything?

Do you have the minimum required batteries on the system?

Not forgetting @cedricr21@hotmail.fr here.

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Daniel avatar image Daniel Alexandra ♦ commented ·

Hi @Alexandra ,

thanks for your help, truly appreciated!
We checked the Pylon battery at the terminals and there is no voltage at all. Battery is switched on and started... 0 V, zero
I read about it that it goes into deep sleep when discharged too much. That seems to be the case here, right?


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cedricr21 avatar image
cedricr21 answered ·

I have an identic problem with my multiplusII, multiplus Say 51,8v and pylontech Say 50v. All connection are correct. I have put smartsolar without ve direct for charge batterie normaly, but i wish have the solution..,

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cedricr21 avatar image
cedricr21 answered ·

je viens de changer les 2 câbles entre multiplusIi et pylontech. Multiplus indique toujours 1,8v de plus que la tension réel. Le problème semble bien venir du multiplus II

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Chris avatar image
Chris answered ·

Similar issue
But it seems more of a drift than an overall inacuracy.

voltages-current.png


Multi VBUS and the two MPPTs seem to closely correlate - but the Pylon varies under use - Charge / Discharge. Doesnt appear to be load related.

US2000C modules

Annother site using US2000's - Nattery BMS / VBUS are pretty much bang on with each other. SOis this a C bersion battery issue ?


voltages-current.png (243.8 KiB)
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hominidae avatar image
hominidae answered ·

In my setup (3ph MP2-5000 + 6xUS3000C, PV on AC-In, no MPTT) voltage graphs von BMS/GX and VEBUS do match fine and no drift shown. I doubt, that this is related to the Pylontech Models (C vs. non-C), hence.

Maybe in your Pylontech stack, the Master Battery is not the one with the latest Firmware, as required by manual. Also, AFAIU Pylontech has different production sites and with supply shortages did make some changes in the BMU circuits, so perhaps one can not just use the one with the latest S/N as Master - but this is a wide guess).

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lucca371 avatar image
lucca371 answered ·

In my ESS system with Multi 5k, 2 MPPT's and Gobel battery there are also different voltages when the battery is fully charged and the BMS shows CCL=0A. The difference is also about 2V. If CCL=0A, the power of the MPPT's is regulated down and the excess PV (DC coupled) is no longer fed in.
As long as the battery is not full (CCL>0A), the voltages displayed by the Multi and the BMS are identical. Only when CCL=0A does the voltage drift apart by 2 V and fluctuate strongly.
It is probably due to the disconnection of the battery when CCL=0A?
In this case the BMS shows 53,6V and at the batterie terminals i measure the same voltage the multi show (i.e. 55,1V heavily fluctuating)

In DVCC when I lower the managed voltage to 54.4V (CVL=55.2V) CCL>0A stays and the voltages match and the MPPT's work at full power. The battery still reaches 100%.
I haven't found any other solution.

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