I have 6 x 200 Ah LiFePo4 12 V smart batteries, 3 x 2, so 600 Ah 24 V system on my sail boat. Solar panels are 3 x Maxeon Supower 430 W, so 1290 W. And the regulator is MPPT 150/60-Tr.
I generally use 10 to 40% of the 600 Ah capacity per day.
My MPPT is on Lithium mode, screw on n°7 position.
During summer in the Med, absorbtion is finished around 10:30/11:00 in the morning after 2h at 28.4 V, then it goes down to 27 V for the float stage.
My question: is it OK to keep having these 2h at 24.8 V everyday?
Does it have any impact on batteries life time?
Thanks for any assistance,
Philippe
I suggest that you read the battery manual so you know how to look after these well, linked below.
To answer your specific question, no this is not ideal and is covered in section 5.2 of the manual. Extract below. I have a similar use on my boat with Victron NG Smart Lithium batteries and for daily absorption use 15 minutes giving 7.5 hrs per month.
We recommend a minimum absorption time of 2 hours per month for lightly cycled systems, such as backup or UPS applications and 4 to 8 hours per month for more heavily cycled (off-grid or ESS) systems. This allows the balancer enough time to properly balance the cells.
Thank you for taking the time to respond, but this is precisely where I get confused.
I have read the manual over and over again and it says that absorption should be set to 14.2 V. Set in the Lithium mode, the MPPT goes to 14.2 V everyday. Nowhere do I find any suggestion by Victron that it is not good. Victron only urges to apply that voltage a minimum number of hours, depending on use, without suggesting not to do it everyday.
I can set absorbtion voltage to 13.5 V under user mode and remember to move it to 14.2 V twice a month. Should I understand that this would improve batteries life time?
Or do you suggest to keep 14.2 V absorption voltage and reduce time to 15 mn/day?
If you keep to 13.5V then you will not recharge at a very high rate. This is why have a daily absorption to get a good recharge even if I only use the engine for 2 hours. You want to spend as little time in absorption as possible, just enough to keep the cells balanced and 15 minutes is OK for me and fits into thrir guidelines.
With 1290 W solar panels, I don’t need to run the generator or the motor alternator to charge the batteries.
I now hesitate between keeping the absorption voltage down to 13.5 V or drastically reduce the absorption time…
Back to the subject and trying to find the right amount of absorption time per day.
Is the adaptative time that appears in the MPPT expert mode setup a way to deal wit it?
In practice, it leads to 20mn at 28.4V absorption voltage per day.
It sounds I have 3 possibilities:
- I could set abosption to 27V and add 2 hours at 28.4V avery other week.
- Or have 15mn at 28.4V everyday,
- Or use adaptative mode that will do 20mn per day in practice.
What would you recommend?
Thats almost like asking what the best religion is 
The important bit is, that the balancing gets activated regularly enough to keep individual cell voltages close together.
Going two weeks without balancing, if we assume that your batteries dont balance at 27V, while cycling them daily might be a bit long. If you can see individual cell voltages somewhere you can try it, keeping an eye on them during those two weeks. It can work if your cells are all very similar in capacity and internal resistance. But for me the manual change of absorbtion voltage every two weeks would be a risk, because i would forget about it at some point.
In my daily driver workvan i use adaptive absorbtion with 10min limit. You can literally watch it reach absorbtion voltage and balancing starts, and two minutes later the charge current is near zero amps when the battery finished its balancing.
The challenge with solar is that there can be bad days, and after a few of them, absorbtion time should still let the battery finish its charging and balancing. Both your suggestions 2 + 3 sound good to me, just check in on how the charging goes after a few bad days