I was wondering if everything is correct on my solar system regarding to the absorption times. I have a 160W panel with 136Ah Sunwind AGM battery. The charge controller is Smartsolar MPPT 100/20 and it has the default absorption values set in the app (tail current 1A and absorption time set to adaptive).
Absorption time is often only for a minute or minutes. Is this normal behaviour for the MPPT charge controller? If I understand the tail current correctly, the charger goes to a float charge after the charge current falls below 1A or after a specific time has passed. I think the charge current is often below 1A in the morning when the bulk charge reaches the absorption voltage. So how can it work correctly if the charge current doesn’t even reach 1amps? Or am I mistaken and the current needs to be more than 1A to reach the absorption voltage, which is set to 14,4V. Could anyone help me with this matter?
I think the problem might be that my offgrid solar system is located at northern Finland where the sun is up 24/7 at this time of the year. And with the solar altitude being low mostly and only going high altitude midday to early evening. So the charge current is often below (or about 1) amps when the voltage reaches to absorption voltage. And this causes the absorption stage to stop prematurely and only after 1 minute.
So maybe I should set the tail current even lower?
If you are getting to absorption voltage of around 14.4V at 1A current for 136Ah AGM battery then it is full. With lots of solar hours you will find that your battery is not discharging very much so it does not need much charging. You need to avoid overcharging AGM which happens if you keep the voltage at absorption for too long. The lowest I would reduce tail current to would be 0.7A but I am not sure that you need to do this.
The only other reason for this is if the battery is at end of life and has lost lots of capacity.
Thanks alot for the quick answer and help. I think I will keep the tail value at 1A for now, since it’s already clearly below the recommended 1 - 2% value from battery capacity.
Indeed the energy consumption is rather low right now in the summer. We’re mainly charging some mobile devices and led lights abit. But we need electricity more in autumn when solar energy is much lower and we probably could connect the fridge to the 12V system instead of gas for summer. The agm battery is brand new.