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Old 31-01-2021, 10:47   #1
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Domestic 12v batteries not going above 13.1v with 500w solar?

Hi all,

Just after some advice as not sure if I have an issue or not but first time at anchor for a while and we have 4x125w solar panels fed in pairs to 2 x mppt controllers. Also have a domestic/house battery bank of 470 ah (1 x 180ah, 1 x 185ah and 1 x 105ah). Yes I know I should have all the batteries the same but this is not anything to do with the issue I believe.

Anyway, even on a very sunny day here I am greeting at least 8a per pair of panels, so 16a total. But for some reason the house bank will not go above 13.1v and then by the morning it is down to 12.1v.

We do have a separate fridge and freezer, as well as nav instruments on overnight but the fridge and freezer compressors are not always on, reckon about 10% of the time.

So, is it because the batteries are always drawing a load they will not go to float?

Should I worry too much about the house bank getting to 12.1v overnight as that is shike it is under load?

On shore power the batteries get to float as that is with a 30a charger.

I am going to change the house batteries and upgrade the bank at some stage anyway.

Cheers
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Old 31-01-2021, 11:15   #2
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

The answer is very simple, you are pulling more power OUT of your batteries than you are putting IN.

That obviously can't last for very long before your batteries turn into nothing more than expensive lead bricks.
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Old 31-01-2021, 11:26   #3
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

BillKny is right, but I'll add to it and say you may be producing as much power with your solar as you use in a 24hr cycle, but due to charging inefficiencies you aren't replacing enough power in your batteries. And FLA batteries are sensitive to partial charge/discharge cycles, which tend to limit their lifespan.
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Old 31-01-2021, 11:53   #4
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Sounds normal for the amount of solar and power draw
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Old 31-01-2021, 13:01   #5
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Cheers, gather tomorrow I will check all the wiring form each solar panel is good as a start and then check each of the MPPT controllers.

We have the generator to use if needs be but would rather not depend on that as thought 500w solar would be more than enough for our usage.

Could it be the batteries on their last legs I wonder?
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Old 31-01-2021, 13:42   #6
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

I will be the fourth to say you probably just dont have enough solar panel capacity. Plus you didnt say where you are located but for us, this time of the year the sun angle is such that we get less efficiency. And i suspect unless you are in cold temps, refrigeration running 10% of time is an optimistic estimate. As per float, if each refrig/freezer are really running that short, that leaves about 80% of the time there is no load, and then your contoller should drop to float if the batteries are full.
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Old 31-01-2021, 13:48   #7
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Quote:
Originally Posted by davethedog View Post
Cheers, gather tomorrow I will check all the wiring form each solar panel is good as a start and then check each of the MPPT controllers.

We have the generator to use if needs be but would rather not depend on that as thought 500w solar would be more than enough for our usage.

Could it be the batteries on their last legs I wonder?
I'm a self taught DIY solar charging person so I'm just talking from our experience. Others will correct me if I give any bad advice.
I wouldnt necessarily blame the batteries. Try running the generator for say 1 hr in the morning & then see if the batteries come up.
We get over 10 amps out of our solar in peak sun & only run a small Engel fridge & anchor LED overnite & thats fine for getting the batteries up to float by midday ( nominal 225 amp )in general. But running the fridge at freezer temps & nav instruments might well put it well behind.
The best way to find out what is going on is to put a watt meter on your power supply & see what you use in 24 hrs & compare that with what your panels produce.
As others said its most likely you are using more than you are producing.
You are definitely aging your batteries faster if you dont get them up to the point that they switch to float voltage & have some hours at that.
Good idea to check everything as you plan to do.
Have a look at Battery University or Mainesails advice on battery charging.
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Old 31-01-2021, 16:28   #8
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

you are producing 16a. (this is 200watts from your 500w solar) maybe for 5 hours / day this time of year? so that is 80ah per day you are making.

when you wake up at 12.1v your battery bank is at 50% so you are down 235ah

so if you turn everything off it would take 3 days to get them charged. ( 3x80ah to get the 235 back)

but durring the day you are probably using 100ah+

so you wake up with 50% batteries. put 80 in and take 100 out and when you go to bed you are still at 50% batteries. slowy draining and never charging. you are just slowing the drain.


what you need is a battery monitor like a victron 712 to watch your battery usage

you probably need to run the gen in the morning for a couple hours each day. though with the 30a charger you are wasting your time. get your self an 60-80a charger. then maybe you can run for 1 hour a day instead of 3 hours a day.


upgrading or changing the bank does not solve this issue. you are using more then you are charging.

I would also look at why the 500w solar is making 200w. but that is likly normal for winter. since both pairs are equal.
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Old 01-02-2021, 04:57   #9
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Bit more of an update:

Have disconnected all loads from the 12v house bank and even with the blazing sunshine here in Gran Canaria we are still only seeing a charge of 1.7A going to the batteries. I have also realised that the Victron MPPT controller is not actually putting any charge into the battery bank at all (this is connected to one of the batteries). Even though i have tested the panels coming into the MPPT and the output which both seem in line with the what the Victron app is showing.

So, any further ideas as next step is to test all the batteries with a load tester as thinking they may not be good, or that the Victron MPPT controller is not good (but the input and output terminals seem fine).

Forgot to mention, we never used to have this issue in the UK at anchor...so thinking it could be the battery/batteries?

Thanks

So, could a defective battery be causing these issues?
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Old 01-02-2021, 05:25   #10
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Might be worth checking the little fuse on the MPPT first.

After that,the cables that go from the MPPT to the batteries with a clamp on amp meter.

I suspect this is going to be a difficult to find but easy to fix problem. Broken wire or poor connection etc.

Pete
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Old 01-02-2021, 06:40   #11
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Well it will give me something to do I guess lol.

Am erring towards a dead battery in the bank but will have a proper look tomorrow.
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Old 01-02-2021, 06:56   #12
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

When you have the loads on is any more than the 1.7 amps going into the battery?
If a battery is really knackered it wont accept a charge but yours are running your fridge etc overnite so I doubt thats it.
Still no harm in testing them.

I'm with Pete7, more likely faulty MPPT or broken wire etc.
MPPT's arent that reliable apparently.
Our Chinese one only lasted 3 weeks lol. Admittedly it was lowest end.
PWM been going 5 years
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Old 01-02-2021, 07:57   #13
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

Thanks and going to look at adding a busbar into the system from the mppt controllers so they go to all the batteries directly rather than to one battery and then to the others.

Think I will get 3 new batts anyway, all the same type and capacity this time and thinking of agm rather than sealed lead acid.
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Old 01-02-2021, 10:02   #14
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

I had a similar amount of solar and battery capacity. my batteries were brand new and the solar 1 year old so I thought the 12.1v was just how it was. it wasn't until I moved onto the boat a year later that I found i had a dead cell... probably there since new.
buy a specific gravity tester. they are cheap. and check each battery cell to make sure you don't have a dead cell bringing the whole thing down.
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Old 01-02-2021, 10:13   #15
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Re: Domestic 12v batteries not going above 13.1v with 500w solar?

I don't know that another data point will help but here you go.
Location Bahamas
House 4xT-125 (480Ah) 18 months old
Four panels going to two Victron 75/15
2X (72w + 108W)
On anchor DC uses - Refrigerator (est. 720Wh / day), lights, phones / tablet / laptop charging


Our panels would regularly generate over 1KWh per day bringing the battery voltage up to 14.5.


I think you are on the right track of needing to go through the system to track down the culprit. The idea of seeing if your generator can do better might help you decide where to look. If possible you might start taking one battery at a time out of the circuit and see if charging increases.


Harry
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