Absorption voltage with 100/20 MPPT Controller

DIY
1

I have a smartsolar mppt 100/20 feeding 3 x Lead Acid Batteries. The Absorption voltage is set to 13.8v. The battery voltage is provided by a BVM712 to the Solar Controller via bluetooth and the voltages transmitted by both the mppt and the bvm are within a few millivolts of each other. However the battery voltage never seems to exceed about 13.6 v when in absorption mode, Does any one know why this might be and how it might be corrected please? Many thanks..

2

How large are your lead acid batteries and what solar power do you have, what is the max current seen when charging, how much power do you use.

It may well be that your power input is too low gor a large battery bank so you never fully charge it, or the batteries are failing and have some shorting.

3

Thanks for your reply. 3 x 110ah batteries. The solar panels via the mppt can achieve 15A charging - certainly sufficient to raise the battery voltage near to the 14.4v transition point. However, when in absorption mode, the charge current is reduced settling at a 13.6v applied (and measured) voltage at the battery terminals.

4

I am confused now.

You say the batteries can reach 14.4V transition point, 14.4V is normally absorption voltage, but you say this is set to 13.8V and only get 13.6V in absorption, which is more like float voltage.

Using Victron connect post screenshots of your battery settings and the history plot of battery voltage and current.

One thing to be aware of is the MPPT varies the charge voltage with battery temperature. Hotter temperature, lower charge voltage. This may explain what is happening.

1 Like
5

I have to agree with @pwfarnell; I think you have a PV array/battery bank capacity issue. We will know more after you answer his questions.

Basically, the bank is 330Ahr. A lead acid battery will accept about 20% of capacity so your bank will accept 66A. The maximum of 20A from the MPPT just may not be enough to (1) bring the bank up to the abs. voltage while (2) supplying DC loads.

6

Thanks for both replies. I think that you are correct 8n that it may well be temperature compensation. It was indeed a very hot day when I recorded the voltages. I will try again on a cooler day and see if at least tge voltage at which it stabilises is nearer the 13.8v that is set.

Thanks again.