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Hy guys.After a certain load,usually usually 3500-4000w the MPPT stops and everything runs only from battery.I have a pylontech US3000C with BMS that i keep only for backup with small loads at night.But daytime I want to use as much solar power as I can.Discharge current on console is 37A but my BMS deactivates the MPPT ....whats going on ? UPDATE : I have added another US3000C to the system but nothing changed.
You appear to have AC disconnected, with one battery that is terribly undersized. The system has to lean on the battery for load transitions, Unbalanced systems, no grid etc will cause instability with undersized batteries.
There should be at least 3, preferably 4 for systems like that.
Mppt's are slow and the bank needs to be able to supply/sink large load variations, one US3000C will not be up to that job.
It is a great way to damage a battery.
The BMS is probably going into protect and blocking charge.
It is a flaw to only design for the small standby load.
MPPTs are slow, they ramp up/down, they also have to track. While ramping the battery must be capable of supplying or accepting the loads, in your example that is up to 4kW.
Without grid, if you turn off a 4kW load, the MPPT is still producing power, which has to go somewhere, the system will try honour limits but it simply can't.
This leaves it up to the BMS to deal with, and pushing or pulling that amount of power will cause issues with the BMS, which, when controlling the chargers will cascade.
It can also balloon your cells, destroying the battery.
You have to size for the larger of the two requirements which is why the sizing minimums exist for ESS and why they are more severe for scenarios where grid is disconnected.
There are countless posts of people with issues as a result of too little battery.
Does the CCL by any chance go to 0A (or a very low number) at this time, since you are near top of charge.
The grid is not disconected.The system is set with Virtual switch and the grid is re connected after some rules that i set in the rvsc file.
1 rule : if load on inverter is bigger than 3500w for 1 second the grid is reconected,and it is disconected when the load is smaller than 3000w for one minute.
2.If battery voltage drops under 49v for 2 seconds the grid is reconnected and disconected again after voltage is 52v for 5 minutes
3.If battery is at 90% the grid is reconected and is disconected after voltage is 52v for 5 minutes.
So the battery cannot balloon or destroy because in any of the cases the grid is reconected.
I also want to say that these loads come slowly.There is no 4kw load just appearing out of nowhere.
The CCL varies.But it goes to 0 when battery is full.Max is 15A.Discharge is set at 37A by the BMS and here is another problem that i see.When this problem that i explained happens,the battery can discharge even with 70A...which I dont understand.
I dont think the system is a flaw,its working perfectly for my needs.I only need the battery at night with small loads and during day i want to use as much PV power as it is available.And i think the rules from the rvsc file are doing their job at protecting the battery.
The inverter limit is 3700w and I cannot even get to 3000.I should be able to get there without buying 3 US3000C that cost 3500 Euro and will do absolutely nothing for me.I have a very stable 3 phase connection,and i installed this system for self consumption and no injection.
And the MPPT is rated for 5800w,so it should give me my 3700w for the inverter load and have some spare to charge the battery,and some more spare.
Screenshot_2023-09-30-12-20-35-68_40deb401b9ffe8e1df2f1cc5ba480b12.jpg
If you're using a virtual switch then you aren't running the ESS assistant, unless you are mixing terminology, that won't help.
While your virtual switch is reconnecting the grid, and letting that synchronise, where does the power go/come from? Yes, the battery, because reconnection isn't instantaneous.
The issue is not the rating of the gear but that the battery is being forced to operate outside of its spec while power for loads are managed and the mppt/inverter ramps up and down.
With grid dropped, a CCL of 0 and load/mppt variations, the battery will not enjoy the transitional loads you are subjecting it to.
How does it behave when you disable the VS and leave grid connected?
I would suspect better.
The minimum requirements for an ESS of your size are documented, they exist for a reason.
Until you either a) increase your battery pack or b) disconnect loads, you will continue to have instability in a configuration like this.
Like it or not.
Did you consider using ESS instead?
https://www.victronenergy.com/media/pg/Energy_Storage_System/en/index-en.html
In off-grid the discharge current can't be limited, the Inverter is pulling from DC what is needed to supply the AC load.
Maybe you have a cell imbalance? In VRM go to advanced and there you can add a diagram of the highest and lowest cell voltage.
Or you look in the remote console -> device list -> Pylontech -> details -> there you can see the highest and lowest cell voltage in real time.
At parameters you can see the current CCL and DCL coming from the battery.
Finally I got ESS working,and also added a second Pylontech US3000C to the system.But nothing has changed,if the total MPPT load is higher than 65A the MPPT will receive a stop signal.( i presume from the BMS..).Funny thing...no errors ...no alarms,nothing.MPPT just stops and starts...If i got errors or alarms it would be better....Clip attached with the system running ESS and having the same problem.
Thats just my unqualfied idea, so it might be totally off.
One US3000C is rated with 35A continuous load. You have two, so we say 70A.
The MPPT peaks a couple time to 3500W, which at 50V means about 70A.
As with VS and ESS alike the Grid can go away at any given time and needs about 30-60s to connect back once available. Could it be that the BMS uses the continuous load to caculate when to protect its tush? Not the peak load (which should be able to handle 140A for 60s (peak1) and 200A for 15s (peak2))?
Very weird behaviour, but my guess is the same as others. It trips over 30 amps on the pv side, but that translates to way over 70 on the battery side. And since bms controls the mppt, it shuts it down. I never encountered this problem in the past when i had only one 5kw array, but maybe because i had minimum 200Ah, 4 50Ah pylons. Now i have 12kw pv, i m willing to test it myself. When i get a sunny day i ll plug in the water heater and disconnect all the batteries except 1 us5000. I ll let you know what i get.
I have 3 Pylontech US3000C,so thats 3x37A which is 111A that can be tolerated on the battery side,and MPPT can put out 100A max.The bigger problem is that i dont have any errors what so ever,when i look in the pylontech menu the is no overvoltage,no overcurrent....absolutely nothing.Everything is ok,the battery says its ok.And i dont think the MPPT should behave like that,shouldnt it throttle up/down?.This stop/start is not right.If battery menu says charge rate 111A in real time...why is the MPPT stopping at 60-70 ? And i repeat,the is no overcurrent alarm on the battery,because if there was i should see it.
Can you go into mppt settings and look up max charge current?
I have no other ideas, 3 x us3000 should be more than enough for the job. Maybe talk to your distribuitor to open a ticket to victron about your mppt, it s worth a try
