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momonu avatar image
momonu asked

Adaptive absorption after deep discharge several days ago

Hi, I do have two AGM batteries with a total of 190Ah, 200W Solar Panels and a SmartSolar 75/15. It happens that my batteries go down to 50% and due to not enough sun the charging back to 100% takes a few days. But then only 50 minutes of adaptive absorption is applied. As far as I understand 4 hours would be preferable after a discharge to 50%. But as there are other days where the batteries only move down to around 80% and are fully charged again the same day, 4 hours absorption may not be the best option for every day? Do I understand correctly? And what is the best setting to use? Should I change the setting once a while to get a full 4 hours absorption?


screen-shot-2021-08-21-at-162802.jpg

The image shows a 50 minute absorption time today, after 6 days of bulk loading. The batteries where down to around 50% on the 17th. Thats when I turned off the fridge to get them charged again.

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JohnC answered ·

Hi @momonu

The actual time spent in Absorb isn't really that important. You've been putting charge back in over days, and that all counts too, whether Abs has been reached or not.

What is important is the current the batts can accept when the algorithm decides to finish Abs. That's the 'Tail Current', and you may find that your mppt even has a setting there that's overridden the algorithm. That's not a bad thing, actually a great feature to prevent too much time in Abs.

I don't know your batts, but my setting (floodeds) is equivalent to ~6A of your 190Ah. This is useless with concurrent loads interfering, but with a BMV or Smartshunt can be networked to pass on the actual battery current, so that can then be used for a reliable Abs termination.

What you choose is up to you. Adaptive alone works pretty well, but the Tail function is a step up. Study what's happening in your system and give it a try..


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momonu avatar image momonu commented ·

Great. Thanks a lot for your explanation @JohnC. I do have a SmartShunt installed. What I do not understand is the mechanism of the tail current. If the controller is using the current reading of the Shunt and there is a load, let's say typically 1-4A, and the charger delivers around 8-10A around noon, how would the 6A tail current be determined? Could you explain this a bit more? And why 6A? I would very much appreciate this. Thanks

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