I have a MultiPlus II with a PylonTech UP5000 battery as a backup system for Eskom. (I have no solar panels.) The system is linked together with a Cerbo GX. The battery is linked with a Type A cable to a BMS-CAN port.

The system kicks in when the Eskom supply goes down and then hands back to Eskom when available again. Immediately after handing back to Eskom the battery will charge to 100%, usually in less than 30 minutes.

However I find the following behaviour of the SOC and the battery voltages quite strange. After being recharged back to 100% the SOC will remain at 100% while the battery voltage drops slowly. The battery will not recharge again until after the next drop in Eskom supply. It will then charge back to 100% and start the slow voltage drop again. See the attached diagram. (Multiplus setting for charging: Absorption Voltage: 53, Float 52.3.  Various settings have been tried but to no avail.

I hope someone can throw some light on the situation.

Have you had a look at the Victron/Pylontech documentation for the correct settings -> Victron & Pylontech UP2500, US2000, US3000, US2000C, US3000C, US5000, US5000B, UP5000, Phantom-S, Force-L1 & L2 [Victron Energy] As I understand it lithium batteries will not float charge unlike lead acid.

When Victron released version 2.90 of the VenusOS for the Cerbox GX one of the changes as per the release notes was for the following:

·          Inverter/chargers: show state as "Ext. control"; instead of Bulk or Absorption, when controlled by a BMS/DVCC. When controlled by a BMS the inverter/charger would never show float, which caused questions. Now it just shows externally controlled, simpler, and more accurate: there is no bulk -> absorption -> float charge algorithm when controlled by BMS.

Edited May 4, 20233 yr by JKKM

Some inverters use the float to cut off as measure for %.

What is your cut off setting?

Edited May 3, 20233 yr by Eurard

Thank you to all for the responses. It is appreciated.

JKKM: Thank you for that note from Victron. This may explain the LED's and the no Float situation. Interestingly - the inverter LED's still goes through the Bulk and Absorption stages during recharging and then once the battery is recharged, goes back to BULK. 

What is not clear to me, is why the battery BMS does not request little refills as the voltage drops after the initial recharge.  After my initial query on the 1 May I did see a recharge request when the voltage dropped below 49V. (With all the loadshedding taking place, this does not happen often.)  But why wait so long? And also why does the SOC stay at 100% as the voltage drops.

 

SuperFly: Interesting that your system gets to Float. Your system has a complex combination of batteries. If I understand you correctly, the MPPT controls the recharging. Is this equivalent to the Victron charger controlling the recharging? Before I installed the Cerbo, the Victron was controlling the recharging and then the system also went through the various phases and ended up in Float.  With the Cerbo the situation changed.

Eurard:

The settings on the Victron are as follows:

Current low shut down voltage is 44V.  (With the current loadshedding schedule it never gets near this value but I will increase it to 46V anyway)

Absorption Voltage: 53V (Victron recommendation for UP5000: 52V)

Float Voltage: 52.3V (Victron recommendation UP5000: 51V)

I have tried various settings but it made no difference.  However, given the feedback from JKKM, I am no longer concerned about Float and the LED's on the Victron. I am just trying to understand why the PylonTech BMS waits so long before requesting a fill-up.

 

Thanks again for your feedback

 

Hi,

 

Okay out of interest what are your other settings:

To Grid

To Battery

etc.

By way of comparison my system behaves pretty much exactly the same. US3000C plus 4 US3000 connected to a 8KW Quattro, Venus GX and 4 charge controllers for the solar panels. The BMS is controlling the charge current limit and sets it to 0 once it has finished balancing the cells. It takes a voltage drop to below 51V before it allows the top up again. The Quattro always only shows BULK and ABSORPTION never FLOAT. The same for the charge controllers. I have the ESS assistant loaded onto the Venus with the parameters from the Victron/Pylontech setup page. The mode is set to -> Optimized (with BatteryLife). Batteries cycle daily. Victron limits the charge voltage to 52.5 via the Venus GX for the reasons they mention on the setup page even though the BMS says 53.2V Never had an issue. You get what you pay for with Victron and Pylontech.

Same setup as you using recomended CVL parameters and seem's to behave the same.

Hi All

It has been a while since I raised my initial question. I appreciate all the feedback and information and in general I think I understand the Victron and Pylontech interplay a bit better. 

Since the last communication I added another UP5000 to the installation. As one of the experiments, I ran it with and without the CAN interface cable. Without the CAN cable the Victron manages the charging. Also early in April a Victron/Pylontech installer configured ESS on my system in an effort to resolve the Bulk/Absorption/Float question. I removed the config later as the ESS charge curves looked a bit messy – it was just my novice view. At that stage I did not understand that the BMS overrules the inverter control.

The following graphs shows the Voltage/Current and SoC for the three scenarios. Also see the comments in the charts.

1) 2xUP5000 BMS Managed Charging

2) 2xUP5000 Victron Managed Charging (on subsequent post)

3) 1xUP5000 ESS configuration (on subsequent post)

I still have many questions but at this stage I am going to go into observation mode and hope to learn more from the other people/users over time.

1) PylonTech BMS Managed Charging (Date of graphs: 3-5 June 23)

2X UP5000 (Simple implementation, no Assistants)

Only the maximum charging current provided in VE Config is enforced by the MP2. (The BMS sometimes shows that it will use 100A to recover from a low SoC. However I specified 60A as maximum charge current for the two UP5000 batteries). Other parameters like Absorption and Float voltages are BMS prescribed. The charger sequence (e.g. per status lights) follows a combination of Bulk, Absorption and back to Bulk sequence. It never goes to float. This confirms what JKKM indicated in his reply above but I was still hoping that there is some meaning for these charger indicators. However I could not see any link between the charger indicator lights and the actual charging stages as per the voltage curve.

All that is abundantly clear is that the BMS controls the charging. After a full charge, the voltage stays roughly constant at 52.3V for what I would term an “absorption” period and then slowly drops to just below 50V. At some stage at about 49.8-49-9V the SoC will show a small drop and that seems to be the signal to initiate a small kick back to 52.3V.

The rate at which the voltage drops to 50V is not always the same and seems to depend on how long it was at the “absorption” level and that in turn seems to depend again on how big the SoC recovery current was. Also interesting is how long the voltage can stay constant at about 49.85-49.9V. Again this is variable.  These variations are a bit weird – I am sure there is an explanation…

Note: these are just my superficial observations and I am sure other people will have more information/detail.

The following diagrams are screen dumps of the voltage/ampere and SoC curves. It includes one loadshedding period.

(I also show some graphs for all of the three measurements in VRM: Battery, System, VE.Bus. )

Comparison between System, VE Bus and Battery recordings of battery voltage (BMS Managed):

Interesting finer detail on the VE Bus report?

To be continued -

Follow on previous reply:

2) Inverter Managed Charging (Date of graphs: 20 May 2023)

X2 UP5000; Absorption @ 52.3V, Float @ 51V, No assistants

(Window includes a loadshedding period that ended at about 01:50)

This shows the charge curves when the Victron is managing the charging. It goes through the expected Bulk, Absorption and Float stages. It is “nice and clean” and I am tempted to use this as the charging approach. Unfortunately one then looses the BMS battery information in VRM (e.g. alarms, temperature, health, etc). Also not clear what is counted as a charge cycle inside the batteries, but this is actually a problem on all approaches.  

To be continued: -

Follow on previous reply - last one

3) ESS Managed Charging (Date of graphs: 3-5 April 2023 – including a number of loadsheddings)

X1 UP5000; Absorption @ 52V; Float @ 51V.

Charging seems to be done under some combination of BMS and Charger control. Voltage and current curves look messy with continually changing voltage and small current, even the odd push back into the main supply. The charger did not follow the Victron charging sequence of Bulk, Absorption and Float, which indicates that the BMS is still in control (partially(?)). I would like to/need to understand the ESS operation and interface with the Pylontech batteries better.

I hope these observations are of use to other people.

Hi Eurard - re your question on 4 May: Sorry I did not reply. Herewith some screen shots

BTW - I see that the Remote Console specifies a maximum charge current of 50A and VE Config specifies 60A. My previous response said that the maximum charge current is 60A but I think I have only always seen 50A during actual recharging. I will have to check but it seems the Remote Console overwrites the VE Config limit. 

Thanks for your input.