8 Jan 2018
From 10:45 I have channelled two panels with a total max input of 16A into 2x120Ah batteries. Being a bright day, with passing small clouds, the voltage at 11:45 is 15.83 and the current is probably around 8 amps per battery. This fits well within the range dictated by the manufacturers in the table below and*
As of noon I have connected a third battery and the voltage has dropped to 15.45. None of the batteries are warm to the touch and started around 5°C.
**12:30** Charge for 3 batteries: 15.64v and approx 5A each. So if the sun doesn't get obscured by clouds I may get (4h x5A) charge.
![rolls guidelines for 12v 4000 series](https://calstock.org.uk/media/blogs/elf/img/posts/new_electrics/charging.jpg "null")
As the batteries are usually below 20°C, I will set the MPPT to 15.14v before switching to absorption then set the time so that the absorption will last a least 4.5 hours before returning to the current a float charge of 13.9v.
Normal absorption time is calculated as follows:
0.42 of the battery capacity in Ah at the 20hour rate divided by the available current.
So given a current of 6A a single 120Ah battery will require 0.42 of 20 or 8.4 hours, something that has never happened at the voltages recommended in the table above. Comment 1 below is copied from Rolls help sheets: Comment 2 is my set up options.
I'm inclined to disconnect two batteries this evening given there are to be a few cloudy days and use little power.
**13:00** Charge volt down to 15.3 so disconnected one battery and the other two are charging at 15.64v
**14:45** Charge down to 14.5 so switched to MTTP