question

How long has it been since this battery bank was at 100% SOC ?
I do not see 14.4 volts on any day.
What is the voltage setting for Absorb mode?
Flooded or AGM ?
How old are these batteries?
These batteries appear to be chronically under-charged.

They've been a 100% by 1300h every day for the past 30 days at least. They stay at 100% until the sun gets low in the sky in the evening here in Greece.

It never gets to 14.4vas indicated on the charger, but I think that's because of a voltage drop in the cables from the batteries to the charger measuring the battery voltage. There's a Matervolt shunt type monitor that always shows a higher voltage.

Absorb mode 14.4V. Pic of setting attached.

Flooded

They're about a year old and have always exhibited the same charge/discharge profile for these given Med-sunny-day conditions.

Undercharged... How come with the settings on the chargers? It's dark now the near-resting voltage is 12.7V with a few LEDs drawing 0.4A and the monitor saying 98%

Please post a shot of the battery settings in the shunt.

I guess you're getting similar figures from the other mppt. Are the batteries connected as a single bank?

The shunt appears to be monitoring one mppt not the whole battery bank.

The battery monitor is an old Mastervolt CSC on a Combi Dakar. So, no app and screen shot, but BULK is 12.0v to 14.4V rising, ABSORB is 14.4V constant, FLOAT is 13.5V constant (battery current less than 2% of capacity). Peukert Exp 1.27P, C.E.F. 90%, Number Cycles 15.

Yes. Two 100/20’s in parallel showing very similar data, but usually slightly different.

Yes. Single bank of 3 Bosch L5 075 flooded LA 140Ah.

Does this help shed any light… At the beginning of today, before the mppt’s started charging and at a typical lowest daily SOC the mppt’s showed battery at 11.96V 0A. At the same time the monitor said 12.04V discharging at 4.2A.

On the charging. The MPPT has to see a battery voltage of 14.4V. At this point it switches to absorption mode, maintains 14.4V until the current drops to the tail current setting. Usually 4% of battery capacity. At the start of the 14.4V absorption phase the battery is roughly 85% charged. Once tail current setting is reached, MPPT switches to constant float voltage.

Your graphs and the MPPT trend shows this isn't happening.

Attached graph from my system showing how it should look. Note my 24V voltage settings converted to 12V are lower than yours due to different battery type. Note also the increasing SOC when the constant voltage absorption phase is reached.

Keygermany, that’s very useful.

My history screen shows bulk, absorption and float for each day. How is this happening if the mppts never see the 14.40V initiation voltage?

Now the batteries are in absorption. The mppts each say 14.20V and 11.90A. While the battery monitor says 14.17V, 21.6A and 95% full. Does this suggest anything?

What should I start looking at to sort this out? Any ideas will be most welcome.

Nevertheless, I appear to have full batteries at the end of each day and adequate power to run the boat. And the daily profile has been the same since the batteries were installed a year ago. If I can’t find an answer is there any way this could be damaging/shortening the life of the batteries?

nickdb (and all), See pic. I turned all off, but the anchor light overnight. The batteries bottomed out at 12.76V. Consequently, they reached absorptions early in the day at the set 14.4V, before it gets ambient hot here in Greece. It then when into float at the set 13.8V. After a few hours it dropped to 13.5V, still in float. I read your comment and turned the -16.5mV/degree compensation of and it went back up to 13.8V. The temperature sensor is in the charger (not a remote sensor on the battery). The casing of the charger is currently sitting at 33C. The batteries are at 27C.

On previous days, after a full overnight load. I think the bulk phase took long enough that the chargers temperature compensation kick in during bulk and the batteries never saw 14/4V. Does this sound feasible?

Do I need to have temperature compensation on?