Batteries charging daily but still decreasing charge overnight

[terah]

Our (newish to us) boat had 3 x Zenith ZGL 12v 120Ah AGM batteries on board. We have added 520W solar with a Victron SmartSolar MPPT 100/50. We're settling into living aboard and have only now spent an extended few days away from shore power.

Each day the batteries reach float, and the SmartSolar reports a max voltage of around 14.26v. Each night the min voltage reported is decreasing, with it last night down to 11.07v.

At night we are running fridge, freezer, and lights, but little else. In the short term we are going to switch the freezer off as we don't really use it. We're also going to swap out the remaining non LED lights. Longer term we'll most likely replace and increase the battery bank as we have plenty solar and want to be able to run fridge/nav/ap/lights on passage without running engine.

For now though, I'm trying to understand why the min charge overnight is decreasing when the batteries appear to be fully charged each day?

The SmartSolar had been on a preset with 14.4v absorption and 13.8v float, which are within the ranges for the batteries (14.4v - 14.9v and 13.6v - 13.8v). Have just changed them to 14.7v and 13.7v.

[smac999]

11v is a totally dead battery. You should not be going below 12v. 360ah is a pretty small bank.

Ideally you'd want a battery monitor / ah counter to know how much you are using overnight or each day.

My guess is the batteries are in bad shape if they are Droping to 11v overnight.

[StuM]

Definitely sounds are though your battery bank is past time for replacement.




But what would concern me first is that reported max voltage of 14.26. According to that, you are never getting to Absorption stage in your charging. Sounds are though your charge is dropping to float too soon.

[MikeFergie]

At least One of those batteries is “dead” for sure and pulling the others down. Split them charge them independently and put a load on and check them individually.

You don’t mention boat size but on my Leopard 40 I have 660amp hours and in the morning my monitor is down to 85%. It just depends of how many luxuries you want running at night [emoji4]

[terah]

Originally Posted by smac999

... 360ah is a pretty small bank.

Ideally you'd want a battery monitor / ah counter to know how much you are using overnight or each day.

The battery monitor is on my list to buy. And ideally I'd like to up the bank to 500 - 600Ah

Originally Posted by StuM

...But what would concern me first is that reported max voltage of 14.26. According to that, you are never getting to Absorption stage in your charging. Sounds are though your charge is dropping to float too soon.

I don't quite understand that part. The Victron app shows the batteries going in to absorption and float, and the respective values are correct.

Originally Posted by MikeFergie

At least One of those batteries is “dead” for sure and pulling the others down. Split them charge them independently and put a load on and check them individually.

You don’t mention boat size but on my Leopard 40 I have 660amp hours and in the morning my monitor is down to 85%. It just depends of how many luxuries you want running at night [emoji4]

We're hauling out in a couple of months so if we can last until then we can do a proper test. If one is bad though then most likely will replace all and increase capacity.

[gauvins]

It looks like your system has been running off the grid for something like 3 days.

1. Notice that the minimum voltage has been dropping steadily, from 12.45 to barely over 11V

2. Your daily yield suggests that you consume something in the neighbourhood of 400Ah/day.

You are almost certainly over drawing energy from a bank that is past its prime.

[Bleemus]

Set Max absorption time to 10 hours. If your batteries aren't trashed yet your problem will be reduced. But looking at it more closely it appears time for new batteries and running the engine more as you have a small bank and insufficient solar to run a fridge, freezer etc overnight.

[Nicholson58]

Originally Posted by smac999

11v is a totally dead battery. You should not be going below 12v. 360ah is a pretty small bank.

Ideally you'd want a battery monitor / ah counter to know how much you are using overnight or each day.

My guess is the batteries are in bad shape if they are Droping to 11v overnight.

I agree. Nominal 360 is small. Only 130 (50%) is really available. How old are they? May be near the end of their life. We are replacing ours this year for the same observations.

[a64pilot]

Everyone is saying they are old and shot.
I disagree, or said another way, they may not be old and shot. I'd say more likely that your charger is dropping into float well before they are charged, and your starting each day on a lower and lower charge so that after only a few days your nowhere near fully charged when it drops to float.

Try this, fully charge them, it is going to take shore power and likely 8 or more hours in absorption to get there, monitor with a specific gravity tester if your proficient using one and tailing charge current if your not. Do not trust you charger to be charged when it drops to float, they won't be, you will have to force it to stay into absorption voltage, often this can be done by turning off the charger, and back on. It should wake up in Absorption voltage. My Sterling Pro Charge Ultra, I have to cycle power four times to get to fully charged. Fully charged for me with my 660 AH Lifeline bank is when charge acceptance rate is only 3.3 amps

Then set your Solar so that it never drops to float, I did that on mine by setting my float voltage to absorption voltage, so that when it drops to float, voltage stays the same.

You may still have to replace your bank, but I strongly suspect if all you do is replace it, You'll be right back with the same symptoms, soon

[zeehag]

test your batteries, but i think you will find that the charge level will drop nightly as a norm. unless you have a battery charger in use 24/7. there are specific norms to consider when using solar and batteries. fact one is charge level drops at night. guess what sun goes away at night

[masonc]

We need to know one thing - how much power you need to consume every night. It looks like you have used 30KWh in four days, so you need 7.5Kwh a day.
That established, if correct, you need to keep your discharge to 75% SOC if your Lead Acid batteries are to last. Therefore, you need 7.5/100*75 = 30KWh storage. 30KWh/12V = 2,500 Ahr @ 12V
Now, if you use 7.5 KWh per day, you have to put back 7.5KWh plus 20% or 7.5 x 1.2 = 9KWh of solar production per day to stay at 100%. More is better.
How much solar do you make per KW per day? Around here that number if 5, and you are unlikely to match the tropics but I don't know where you are. Let's use 4.
9KWh /4 = 2,250W of PV.
You may adjust to suit your real numbers but the formula is real. You NEED to know how much power you consume. On my boat, a very small system, I use about 480Wh per day.

[Stu Jackson]

We're hauling out in a couple of months so if we can last until then we can do a proper test. If one is bad though then most likely will replace all and increase capacity.

Why wait to check the individual batteries?


What is your daily energy budget?


Have you investigated battery monitors and the Smart Gauge yourselves yet?

[Wayfarer1008]

Check the solar panel sequencer, it sounds like the energy you are picking up through your solar panels is bleeding out through the panels at night. Its as simple as placing a diode in the electrical line so electricity can only flow in one direction. That diode is generally in the sequencer but you can just buy on the right size and put it in line yourself.

[terah]

Originally Posted by a64pilot

... Try this, fully charge them, it is going to take shore power and likely 8 or more hours in absorption to get there, monitor with a specific gravity tester if your proficient using one and tailing charge current if your not. ...

We're in a marina tonight, so I can cycle the battery charger to make sure they get a full charge. How do I monitor tailing charge current? On the boat I have the Victron SmartSolar, the boat electrical control panel with meters for volts (per battery bank), consumption, and charge (per alternator / charger). And also a multimeter.

Originally Posted by zeehag

test your batteries, but i think you will find that the charge level will drop nightly as a norm. unless you have a battery charger in use 24/7. there are specific norms to consider when using solar and batteries. fact one is charge level drops at night. guess what sun goes away at night

Originally Posted by masonc

... We need to know one thing - how much power you need to consume every night.. ...

Originally Posted by Stu Jackson

Why wait to check the individual batteries?


What is your daily energy budget?


Have you investigated battery monitors and the Smart Gauge yourselves yet?

I'd figured it would be a lot easier to test the batteries and also work out how much power is actually being used by individual items when we're somewhere where we can easily turn things on one by one, so while hauled out seemed a bit more practical. If there's a simple way to test the batteries while we're still using them then great, can do that straight away.

I've only looked at monitors in the loosest way so far. I'd wanted to see how much useful came from the SmartSolar before working out what to add next. I'd been thinking the Victron BMV but will look at the SmartGauge too.

Originally Posted by Wayfarer1008

Check the solar panel sequencer, it sounds like the energy you are picking up through your solar panels is bleeding out through the panels at night. Its as simple as placing a diode in the electrical line so electricity can only flow in one direction. That diode is generally in the sequencer but you can just buy on the right size and put it in line yourself.

I'd assume this is in the SmartSolar, but not sure how to find out?

[travellerw]

Originally Posted by terah

I'd been thinking the Victron BMV but will look at the SmartGauge too.



I'd assume this is in the SmartSolar, but not sure how to find out?

The SmartGuage is nice, but stupid expensive for a slightly more accurate product than the Victron. To me its a waste of good boat funds to spend the extra on it.

As to the Diode.. YES its in your SmartSolar, ignore that advice as you do not need a diode if are running through a Victron solar controller (or any controller for that matter).