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Hello, I'd love to get some input from the community regarding how they are setting their charge profiles for LifePo4 batteries across Victron equipment.
The standard profile seems to be; Absorb - 14.2V and Float 13.5V - These seems to contradict various articles and research I have done.
Any input would be appreciated.
My battery bank is a rather old LiFePO4 bank. The cells were from an old motorcyle, so they were hammered for the first 10 years of their life.
Therefore, I have more conservative charge parameters: 14V absorb and 13.5V float.
Thank you @WKirby for the reply, that is very useful.
So you have the same Float, but the Absorb is slightly less. Having a slightly less Absorb value, does that mean that the battery wont achieve 100% SOC? Also, how long do you run your absorb for?
Sure, the battery does not reach 100%, but that's not an issue for Lithium chemistries. It just means lower capacity.
Also because the cells are old the Voltages of each cell start to differ a lot more at the upper charge limit.
I set a long absorb time of two hours. This is to allow the cells to balance. My cell balancers are set to shunt at 3.5V.
One day, when I can afford a new battery bank, I'll probably use a short absorb time.
Hi
I have some winston 300ah cells in a 12v battery. Both active, and passive (3.5v) cell balancing.
Despite having enough solar to charge them at .25C, I rarely ever get to charge them at .1C. They either get charged before the sun fully comes up, or shade / cloud reduces solar input.
Anyways, I have set my bulk/absorb voltage to 14.00v (15 mins absorb), and float to 13.4v. At 13.4v the battery can still accept charge (if not already fully topped of).
With higher charge C rates, you would choose higher cell voltages for bulk/absorb.
With lower charge C rates, you would choose lower cell voltages for bulk/absorb.
As to how long the battery should stay at the absorb voltage, I use my BMV to display battery charge A, and mostly the charge will drop to 2% of cell capacity when the absorb period ends.
As always YMMV.
My batteries are 2 years old. I built a 560AH battery using prismatic cells. I've set my absorb at 14.0V as there is so little capacity above 14V, that it's not worth stressing the cells by taking them close to their maximum voltage. In my case, I've tested them and there is less than 1Ah in that last 0.6 V. I float at 13.35V. My absorb is based upon current reducing to 1A. Today, this took less than 5 mins from hitting 14V to dropping to float. There are a further 3.3Ah lost while dropping to the float voltage. My BMS is set to passive balance at any cell voltage above 3.2V. I also have an always on passive balancer. I rarely see a cell differential of more than 5mV and it's normally closer to 3mV. The battery lives mainly between 90% SOC and 100%. Occasionally if I have a few dull days, it will approach 80% SOC. The pack was built to allow me 10 days off grid in bad conditions. The worst I have seen is around 20% in the middle of winter.
We had a 4 day power cut just after I had built the battery and ran the house from the van overnight, then generator to top up during the day. this dropped us down into the 60% SOC range, but the pack performs beautifully.
