I have a 3 phase Multiplus-II system, 48/8000 ,with 500A SmartShunt, CerboGx, and 2 x 24V Victron SmartLithium batteries 200Ah each, connected in series for getting the 48V, plus 4 x 16 cells DIY Lifepo4 battery banks each having 360 Ah. In total 1640 Ah of 48V battery capacity, plus 17.5 kW Fronius inverter for photovoltaic panels and ability to inject the extra power into the grid.
I observed that when the system is ending the Absorption phase (after 1 hours of 56.8V), the system is entering Float mode (54V) but it starts dumping a lot of amps, as you can see, it starts dumping with minus -360A, until reaches plsu/minus 1 - 5A (normal float current).
Is dumping such a large amount of amps normal? I ask because I hear the Multiplusses working hard when Float mode starts with such large amount of current.
That is a small amount of battery for such a large system.
Your inverters, before peak, are capable of sustaining 480A for batteries where recommended discharge is < 200A and charge is < 100A.
That is not a good way of ensuring they last, I would be adding batteries.
Thanks for your reply, but it’s 85 kW of batteries as total storage. I can’t add more batteriess since I will not be able to charge them with a 17.5 kW Fronius.
I’ve noticed when the system was operating with SmartLithium batteries alone (approx 10 kW storage), it was still starting to dump with -80A when was entering float mode. I’m thinking that if I will add more batteries, the dumping current increased too.
I need to mention that there are no consumers from batteries when entering float mode. Consumers are sustained by PV production..
You’re mixing and matching batteries on one system?
That is going to make things interesting, it is also why it is unsupported.
I would be surprised if that hasn’t voided the warranty on your victron batteries.
If the system cannot properly be managed by the battery then it will behave unpredictably.
You have a large difference between absorb and float, so it is unsurprising, in the absence of battery limits that such a large system can dump the power quickly in order to lower the voltage.
A consequence of an architecture that is far removed from best practice.
You have a set of victon batteries paired with DIY batteries - that is mixing and matching.
Pairing different packs with most commercial batteries is unsupported.
If you want to attempt this you would pair batteries with similar characteristics but in this case you have two smaller batteries in series, paired with single 16 cell batteries.
Victron BMS’s are for managing victron batteries only. Since you have a shunt, this would be the way to monitor the complete pack, nonetheless you have combined batteries that really do not belong together.
That’s not how it works. You can’t just throw batteries together because they all contain lithium cells, which come in various forms, packages and specs.
You seem to have bitten off a big DIY project without fully comprehending what is involved.
Since this is a modified system, I will move this topic to that category where others who like being creative with system design may be better placed to advise you.
I didn’t hear that in any post. I’m not very experienced but even I have internalized that you can’t mix batteries like that and get good results. I would suggest that at worst, make another DIY battery with identical characteristics and get rid of the Victrons.
You are charging to 56.8V - 3.55V/cell which is good, a little bit on the high side.
Then when this is done, the system has to bring the voltage down to 54V - 3.375V/cell which is a bit on the low side.
This is what you are seeing… Up until is hitting the float voltage, the system is drawing from batteries, with minimal draw from grid.
So probably, when you measured/seen that, the loads were about 18kW, about 6kW average per inverter, all from batteries.
Once you’ve got to the float voltage, probably the batteries current stabilized down towards 1-2A and power have shifted towards consumption from grid.
All in all, normal behavior.
As a side note, I would charge with max 56V (3.5V/cell) and float at 54.4V (3.4V/cell)
At such voltages, for sure both types of batteries will feel comfortable and you’ll be minimizing the chance of having high voltage runaway cells.
But Fideri’s advice is sound, as there you have two balancing systems in series as far as Victron batteries is concerned.
And they don’t know how to share info for proper balancing, in sync, of those two 24V batteries.
In such situation, you can’t control which 24V battery will reach full charge first and you may have a situation where the voltage on a 24V battery to be way more than it can handle, because the mid point between them isn’t properly controlled to exact half the voltage of the entire system.
Thank you very much for your reply which makes sense about the dumping process. Dumping amps when entering float mode is normal, but I couldn’t find how much, how many, or even at what disch.rate.
The charging process is controlled by Victron’s VE.Bus BMS V.2 with DVCC enabled exactly as per the Smart Lithium battery manual, which works flawlessly for the other batteries too. I can’t control not too much, but I do will stick to the charging curve of SmartLithium batteries.
Anyway, since Victron alone with SmartLithium batteries only was started to dump with approx. minus 80 A, then when I’ve added 4 more batteries, the whole process is multiplied with 5, and makes sense about those -360 start floating amps.
Fideri’s advice might be sound, but this is how the batteries are designed to work and how are connected together to build 48V systems. Thats the purpose of the BMS, to monitor each cell…
This is new info, not told in the first post…
Then, I suppose, it’s OK, because it seems that even on Victron’s documentations they appear in several places in systems with 2 x 25.6V/200Ah batteries in series, with BMS controlling them.
So they take care of themselves.
And the additional batteries, because each has its own BMS, are also taking care of themselves, because your inverter(s), for them, the DIY batteries, is just acting like a charging power source, with proper set charging voltages.
