I have 6 parallel 7kwh Rahvolt batteries all with own bms. When they reach 100%soc the bms stops them taking more charge, but they dint all reach 100% soc at the same time, so when one does while the others are still charging, i get a high voltage alarm, even if the overall soc reads 92%
Is this normal, should i be concerned or just live with it?
The chances are it is a high cell voltage and the batteries need to balance.
When to be concerned depends on a number of factors.
Generally new lithiums have the alarm untill the settle. (Often best to keep them batteries charged for a few days - up to a week)
In the vrm advanced load up the bms cell min and max or look at it under the battery in the device list.
if your system is set up right, then the DVCC should limit the current as the batteries charge to 98%. (This should be done on max cell voltage rather than on SOC, a very common mistake).
It should be possible to reduce the max charge voltage slightly - by about 100mV, so you don’t get this alarm. This may improve as cells balance, but in general should not occur.
DVCC is one area i don’t quite understand and could do with some help with. I have never adjusted any of the settings, so the settings are all at default as in the attached pics.
What should i adjust?
Regarding cell voltages, i only see a total voltage of all 6 batteries combined. I cannot find a setting to view the individual cell voltages from each battery.
Should i be able to see individual cell voltages?
Unfortunately with Venus OS, the individual cell data is not present. The min and Max cell voltage and temperature, and the id of these cells should be visible.
Device Maximum voltage settings are set with either VE-configure (inverters), or Victron connect for mppt’s. DVCC should not override these maximums.
Dynamic voltage and current control enables the BMS to signal the Venus os device to control the charge current and voltage to allow the cells to balance without going into an over-voltage condition. It also works for max discharge - as cells get cold or near to full discharge, the available current is reduced. So the performance of this depends on how the BMS talks to the Venus system.
I tried communucation but did not like the fact my setup could shutdown my inverter so I removed it. You are able to use Home Assistant to get individual cell data and send alerts or errors. A battery near 100% SOC and balancing to me is not useful information.
I use this node-red flow to adjust the charge current in DVCC. When the voltage of the battery is above 55V the current will scale down to 10amps as it reaches 56.5V my max charge voltage which seems to work with my system allows the BMSs to balance. I have put the JSON code in a text file if you want to try it and adjust it as needed.
ADJUST DVCC BASED ON VOLTAGE.txt (5.3 KB)
Thanks for your kind advice, likewise to Mike.
Regarding node red, ive always seen it as a nightmare to know what im doing, even after following several youtube tutorials, i still vant work out how to use it. The txt file looks very full of codes and comands, how do i use this, do i copy paste it into somewhere in node red, or do i need to read it and manually copy it into the node settings?
If i cant fix this high voltage alarm issue, am i potentially causing damage to my batteries, or is it ok to live with the issue? As the system seems to be working perfectly apart from the alarm message.
Thanks for the advice. Is the maximum voltage in VE configur and Victron connect the voltages i inputted when i set the system up at the beginning?
I copied the maximum charge voltage as was in the battery instruction book. I jave uploaded a picture of the instruction book for voltages settings.
Should i change anything?
I have fast charge and float charge parameters on the battery instructions, but i cant remember there being those two settings on the mppts or inverter?
This is normal if they are daisy chained. How are yours wired up?
Ideally they should all be connected to a bus bar with equal length cables.
This will happen because not all of them are full at the same time.
The answer is on all devices used to charge, so yes on the inverter and the MPPT.
What are your settings?
Absorption 57.6v and 56v for float?
Just right-click and select import when you get this popup paste the code for the flow and adjust as required. I have 2 functions in there that have descriptions of what they do its easy to see the values and modify if required.
Have fun and keep learning.
They are all wired in parallel to a common busbar with equal length cables, but first each battery passes through an 80A breaker before connecting to the busbar.
Thats is correct, i set absorption to 57.6v and float to 56v, but why is absorption marked as “fast charge” in the instruction book? And what does Bulk mean on the inverter? I always thought Bult meant fast charging, but theres no bulk settings on the mppt or inverter.
Thanks, ill give it a try.
No idea. I also feel like it it too high (3.6v per cell). Maybe keep the absorption time shorter to help.
Or set both absorption and float the same.
How do i set an absorption time, i wasnt aware there is a timer available in the settings? If i reduce absorption voltage to the same as float, will it take much longer to charge the batteries?
On the inverter there is a way. Setting 12 in ve config.
Depending on how great the battery is at controlling the system (related to external control), this should have an effect.
Ok thanks, ill check setting 12 and see where it takes me. Ill update once ive got round to it.
I was just wondering, being ve config is the settings on the inverter, is this not only for grid charging? Or does it affect the mppt charging parameters too?
The MPPT will be externally controlled with the veconfig settings. It’s important also to set the MPPT to the same settings in case you lose communication from Venus OS.
In an ess system the ve bus setting affects the mppts. It is mentioned in the manual somewhere.
I would set the max charge voltage to 3.55V per cell, This is the Absorption and equalisation voltage - just in case equalisation gets set by mistake.
Float voltage should be about 3.45V to 3.50V per cell . You don’t want much back off for lithium. (This was originally to stop excessive gassing off in lead acid batteries).
Bulk is the constant current charge (CC) of the battery before the absorption voltage is reached. Once this voltage is reached, the mode switches to constant voltage (CV) and the current slowly drops from maximum to a tail current value, after which the volts are backed off to the float value.
Absorption time can be set on Victron’s inverters and MPPT charge controllers, and this then transitions to float at the end of the time - even if the tail current is not reached. This can be the case if there are DC loads attached. With lithium, holding the absorption voltage for 4 hours will normally give plenty of time for balancing. If the float voltage is set too low, balancing may not continue.
The problem im having is with only one battery. I have 8 batteries in parallel, each with their own bms, but one battery seems to always reach 100% soc while the other 7 are still charging in absorption mode. This usually happens when the total soc indicates around 85%
So basically that one battery always triggers high voltage alarm and the bms stops charging it.
Would this eventually damage prematurely the battery, if it keeps going into over voltage?
I cant think of how i can charge this battery separately to the other 7.