Dear fellow diy`s 
Last week I installed my ESS installation containing:
- Cerbo GX
- Victron energy meter
- Multiplus 2 5000VA
- 16x 3.2 314AH DIY battery with JK BMS
Yesterday evening I`ve configured everything including ESS and it bassicly worked instantly.
Today I was monitoring the system en specificly watching closely when the battery was reaching a SOC of 99%. The Multiplus nicely throttled its power to it and went into absorbtion mode.
After reachig 100% it started to switch between discharging and charging (absorbtion) all the time. The charging part once ever x time I can understand but the discharging will solar is producing way enough power I don`t.
Is this normal behavior? Should the battery not be charged to 100% and then bassicly leave it alone until it needs it because solar is not producing enough anymore?
I have pretty close the same setup with different BMS on the batteries. MP2 5000 in 3 phase setup that I configured. When you configured your MP in VEConfigure(after the firmware update), did you notice that there is a setting for the grace period after the absorption hours. Basically a setting for how long the MP will wait until the charger will go for another absorption cycle. After 100%, my multiplus’ charger does go from 500W to -150W multiple times during the absorption. This is because of the BMS’s internal passive balancer. All 6 of my 10kWh battery banks will sent a CAN signal to the Cerbo telling, that all batteries are refusing charging. The balancer is just pushing small amounts of current and discharging 100mA of current per battery for the passive balancer. This is very normal, and after the set absorbtion time, the charger should go to idle Float mode with lower voltage(If configured properly in the MP2 settings). For me the Absorbtion is 52.2V and Float is 51V. This is with a 15S 48V version. You might have a higher voltage if yours is 16S version.
Follow up question. What kind of a discharge load(W) are you seeing even when you don’t need the battery to support the load because of the excess solar yield?
Hi yes the discharge load is around 100 to 150 watts…my absorption is indeed higher because of the 16 pack, I believe it is set to 56.8V
Very much as it should be. The batteries are most likely just balancing(burning energy with resistors from the cells with the highest voltage per battery unit). I have a 2h absorption timer and a 12h wait time until the next absorption cycle will start. 4 out of 6 of my batteries are less than a month old so the 2h balance time if fine. After I get a better top balance in a month or two, I will lower the voltage to 52V an the abs time to 1h. There is no need to push the cells to 3,65V for 2h every day in the long run. It will only harm them. But it will top balance them in the first weeks to initialize them(matching levels). Currently when dropping to 99% in float, my deltaV is 4ms(between 6 x 89kg batteries). Over 250mV when top balancing at high cell in 3,65V. Never let the cells idle for extended time at that high of a cell voltage. 3,45-3,55V is enough for passive balancing(mine starts to balance at 3,45V) and 3,4V is great for Float mode voltage(can be even lower).
Hi,
I top balanced all the cells before I put them all together. I start balancing also at 3.45V whenever there is a differnece of 0.01 volt.
Next month DESS activation, very interesting to see how that will work. I`m very glad I bought Victron equipment and build the battry myself. It saved my so much money and you get so much options with Victron vs Plug&Play batteries…
I planned to build my own in the start as well. Until I found a manufacturer in china that sells ready made units for 790USD for 10kWh with Victron compatible BMS communication.
Much easier to just erect 6 rack type batteries next to the wall and plug them in to a Lynx 1000A buss bar and add cat5 cables. Done.
The difference in DIY price vs that was just too narrow for me to bother. I do understand the “call to build” thou…
790USD for 10kWh. That is a really good deal. I`ve paide about 150USD for 16kWh now. Including a Victron compatble BMS, with 2A balancing capacity.