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robbirobson

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Posts: 13
Reply with quote  #1 
Hello,

i just recently (2 month ago installed solar power in my container).
The system consists of 4 batteries @12V and 100AH, 3KW MPPT inverter (this silver type with blue lcd from china) and 6 Solar panels 24V - 190w. 2 Batteries are in series to have 24v and then 2 and 2 in parallel. I am not connected to the grid.

I am living in central america where the sun is mostly direct and hot, so the system is able to charge the four batteries in 1 full day of sun altough the system never get near its rated output. The maximum i get out of the solar panel direct it is 800w.

The container is on concrete blocks at a hight of about 30cm. The batteries are stored under it directly on the floor.

Now my problem is, that the batteries are always discharging over night and in the morning there is almost no power left. If i use it or not. I turned of everything at night and checked the current at the inverter display, there is just 0. Battery voltage about 26v. I can run various things at night but it will not last. If i run only a 15w ventilator in the morning there is no power left.

So my question is, do i still need to put diodes to prevent backflow of current even if i have a mppt inverter (i guess it should stop the current in the other way?)

And i did some research on the net before because somebody told me not to store lead acid batteries on concrete floor but it seems not to be true anymore. But what could be the cause? I mean this batteries Have 24v at 200AH  should be 4800wh they should not drain by a simple ventilator or even nothing?

stmbtwle

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Reply with quote  #2 
I would disconnect the batteries from the inverter overnight and see if they hold their charge. It will at least give you an idea where to start.

You should not need diodes. The charge controller/inverter is SUPPOSED to do that for you.

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Willie, Tampa Bay
robbirobson

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Posts: 13
Reply with quote  #3 
Yes i will do more testing, i would like to know if anyone ever experienced similar problem? And the storage on concrete would not harm the batteries in any way right?
The thing is also i can run for example my fridge and my computer about 10 hours without sunlight from batteries so the power is there - but if i turn everything off (disconnect by breaker switch) the batteries are empty in the morning and i used to check in the night but the mppt does not display any current flow but voltage of the batteries slowly decreases.
stmbtwle

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Reply with quote  #4 
I remember that claim from 50 years ago but I don't recall ever experiencing it, certainly not overnight. However you are getting a drain from somewhere, and there aren't that many possibilities. Is the hookup correct? Is anything getting hot?

You may have a bad battery. When batteries are in parallel, a bad one will pull down the others. The charging system will "hide" what's going on, for a while at least. Separate the two 12v units at sunset, record the voltage, and check them again in the morning.


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Willie, Tampa Bay
Gordy

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Posts: 86
Reply with quote  #5 
I had it happen (batteries going dead on concrete), I had to clean and repaint a rusty battery box on a US Army Jeep. The next mourning when the paint was dry, the batteries were dead. That was back in 1982, I still place batteries on wood just to be safe.
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Gordy,
Minnesota
stmbtwle

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Reply with quote  #6 
Worth checking, anyway. I have a 'workbench battery' which is normally fully charged. I'll set it on the floor and see what happens.

Hm. Just went out in the shop and found it was already on the concrete, and has been for several days. Still reads 12.6 volts. I'll try again tomorrow.

Concrete is pretty hard. I wonder if the jolt of setting a battery down damages it somehow? Wood at least is a bit softer.

Note that a battery under charge may read over 14 volts. Once the charger is disconnected the voltage WILL "slowly decrease" until it stabilizes somewhere around 12.6-12.7 volts.

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Willie, Tampa Bay
Rick H Parker

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Posts: 653
Reply with quote  #7 
Concrete, dirt, ect draining batteries is a myth. Self-discharge is what drains the batteries, which will happen however the battery is stored. People where and still are unaware of battery self-discharge characteristics, that is the root cause of the myth.

Float chargers AKA battery maintainers where developed to deal with the self-discharge characteristics of batteries.

Most likely he has a parasitic load on the batteries. The experiment Willie suggested would determine if that is the case.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
mvas

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Posts: 9
Reply with quote  #8 
What type of batteries do you have ?
a) Sealed AGM Battery
b) Flooded  Batteries?

What voltage are you charging the battery bank to, during the day ?
AGM = 28.8 Volts
Flooded = 30.0 volts

How do you know that you batteries are fully recharged ( 100% State of Charge - SOC ) every day?

Most likely, you have chronic under-charged and have sulfated the battery bank.

Tell me about the daily CHARGING process (very important) !
a) Bulk Charge at ? Amps & for how many hours per day?
b) Absorb Charge at ? Volts  & for how many hours per day?
c) Float Charge at ? Volts & for how many hours per day?

If flooded type then when was the last time you equalized you batteries?

800 Watts (net) of Solar Power should be enough to recharge your battery bank, if you are not  consuming much power.

800 Watts / 30 volts = 27 AMPS charging current.


mvas

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Posts: 9
Reply with quote  #9 
If flooded lead acid type then have you checked the electrolyte lately?

robbirobson

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Posts: 13
Reply with quote  #10 
Hello ok well, it turned out that one of the batteries was not fully charged, maybe it has been stored to long at the dealer without charging? Its not damaged, i disconnected all and charged the separately to the same level and connected them again. I also raised the charging amperage and voltage at the mppt a bit. As of now it is looking good. System went not down this night. I am just hoping the batteries will still last the promised 6 years as they have been drained way too much.
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