Hello!
Why is the float-voltage noticeable lower than the absorbtion-voltage?
Does the voltage fall so much after the absorbtion-load with a current about 2A?
Or does victron hold the battery-voltage on float-voltage if the battery-voltage drops after charging and there are no loads?
Sorry for my bad english :)
Your English is good.
This for lead batteries in general
Standard 3 stage charging is bulk/absorption/float
Bulk, charge at charger/ battery max current until voltage rises to the absorption Voltage. At this point the battery is somewhere around 80-90% charged.
Absorption, keep voltage constant until battery full. During this phase the current drops slowly as it gets more difficult to push current through it as it charges further. When the current drops to a low value, known as tail current the battery is full. At this point the charger goes into float mode.
Float, use a lower voltage to maintain the charge, but not at such a high level as to wear the battery out prematurely.
You can look at it another way, battery will charge at float voltage, but very slowly. So we increase the voltage for a while to charge it more quickly. Then lower it.
Ok thank you, thats clear until this point:
Does the ESS discharge the battery after absorption-mode down to float-voltage?
And another question:
I have set the absorption-voltage now for my 48V-Lifepo4 on 56,8V and activated the setting "keep the battery full loaded" in the ESS (GX-Touch).
Why remains the Victron-System constantly in "Absorption" although the battery is full?
There are also constantly flowing hundrets of Watts in the battery, on the other second they are flowing out of the battery...there is no "calm" in the battery-current-flowing.
Is this normal?
Is there with so much generator-watts no "calm" possible because the systems use the battery as a "regulation-buffer"?
You might have the same problem as I did when I saw this type of behavior. My absorption voltage was set too high and one of my batteries voltage was going much higher with it being full. The midpoint devation was very low until right at the end of charge, and the one would peak faster than the other. Maybe a slight difference in capacity of the cells. I caught this by setting up the midpoint voltage monitoring the VRM graphs. The total battery voltage was going up around 59-60 volts because of the one battery and then the charger backs off, and voltage drops, and then it will try to charge again. It did this back and forth. All in all, lowering my absorption voltage to 56 volts and float to 54 appears to have leveled it out and fixed everything. Battery reaches 56 volts and then absorption slowly lowers current until tails off over the next hour.
Oh thank you!
I noticed one cell in my pack which voltage was to low but also one cell which voltage was too high, it was already at 3,6V. (Lifepo4 DIY-battery with DALY-BMS)
It looks like that this is the same problem that you describe!
Now with lower Generator-Power the system calm down and went over into float-mode.
Is the following a good idea?
Slowly increase the float-voltage up to 56,8V the next days so that the balancer has a chance to balance all cells (top-balancing) and after this setting absorption/float on 56/54V.
Or you can lower the charge amps so the battery charges slower and the balancer can then keep up.
What type of balancing system is on the pack? Active or passive? And did you top balance your cells before building the pack?
Make sure you charge up to at least the minimum voltage to trigger balancing. If you are at the lower end you can then hold it longer in absorption to help with balancing. Charge slower so you dont get over run on voltage on cells since it does seem the balancer is not keeping up.
2 cells were not in balance, that was the problem. After reaching the voltage and reducing the amps the battery-voltage was falling to fast so the amps went up again and so on...
I did a top-balancing yesterday and now it is a lot better.
I also set absorption and float voltage both to 55,2V (3,45V per cell).
With this setting i only lose minimal capacity compared to absorption at 56,8V.
Befor this i tried absoption 56V and float 54,4V, but here i noticed that after absorption the system discharge with up to 1200W to get down to the float voltage - material-stress for nothing i think :)
Set on 55,2V there is also enough space for fluctuations for the varying PV-power at sunny-clowdy days.
Neat. Moving in the right direction.
Sometimes a cell shuffle can also help, if you have two in particular always going higher move them to the pack centre. The ones in the middle tend to lag a bit in charge in some setups (especially if they are only passively balanced.); Since ohms law is a thing.
Keeping a little under max is always a good idea so they can absorb overshoot from PV. Some guys even argue that lifepo4 doesn't even need a float; but that is a whole other debate. I still lean toward a bit of float / absorption difference depending on bms type and balancing trigger points and type of balancing. Slower charge always on passive balancing with smaller discharge capabilities so it can keep up with run away cells.
