why battery voltage drop much at bigining ?

[Matrix]

hi sunking ,, thanks for reply ,
first what is SOC please .

Hi Zolar, Welcome to the forum. You are getting advice from some folks that really know (not including myself). Listen and Learn. SOC = State of Charge.

Also, to help you get your head around things, it might be helpful to do some load calculations for your daily need of Watt Hours (not watts). It is irrelevant to say "I have a coffee pot that uses 1200w" or "I plan to use 4 12w LEDs". Only you can determine how many Hours per day each of the devices attached to your system will run in a 24 hour period. That is the only way to determine:
- how large a battery bank you need
- The size inverter you need
- And the number of panels to provide the needed Amps to recharge those batteries as fast as possible when you have sun

You really need to do the work of Load Calculation so that you will know what your are demanding and what size system you need to avoid discharging more that 50% per day.

Where do you live? This will determine how much sun isolation you get each day. As SK said, it has nothing to do with the time from sunrise to sunset.

Here are 2 really helpful tools to help you get your head around your daily Loads (needs) and basic off grid system design. Look up the tools "Load Calculator" and the "Off Grid Calculator" at a place called the ALTE Store online - Both are very basic, but helpful in grasping the simplest of basic design. It will help you see visually want SunKing is saying. Simply Google search "alte store calculators" and you will find these calculators.

But as to sun hours for solar, here is a very basic chart ...

Solar Isolation Chart.JPG

[zolar]

when I said the time of sunrise and sunset only to tell you the day time but as I said i calculated the good sun shine as 7 hours just to be sure of sun hours for my panel
and sorry bro didn't understand much for last reply , but I am in united arab emirates close to abudhabi the capital

[Sunking]

first what is SOC please .

State of Charge voltages you are expressing as 100 to 85%.

I am living about sea level , sea only 400 meters from my house although I don't go to sea, and sunrise here 6:20 am and sunset 5:35 pm, and that's I think more even than 10 hours,and at summer more hours by the way,,

That has nothing to do with Sun Hours. You are making a huge DIY mistake. You are associating daylight hours with Sun Hours. They are not the same thing. A panel never ever generates its rated power. At best for a few minutes around noon a panel might generate 90% of its rate power. If you look at the output of a panel is a Bell Curve. At first light the panel will generate 2 to 3% of rated power. As the day progresses power slowly rises and peaks at Solar Noon, then immediately starts to taper down till sunset.

So if you had say a 1000 watt panel operating into the grid where all power is harvested and utilized over the course of the day in Summer you may see 5500 watt hours produced. That would mean you had 5500 watt hours / 1000 watts = 5.5 Sun Hours despite having 14 hours of day light. In winter that can go down to 2000 watt hours or 2 Sun Hours. In that example you design for worse case winter 2 Sun Hours. You are using make believe numbers that are not based on reality.

Where are you located so I can look up your solar insolation numbers?

[zolar]

hi sunking ,, thanks for reply ,
first what is SOC please .
and actual sun hours daily now more than that , I am not living on mountain , I am living about sea level , sea only 400 meters from my house although I don't go to sea, and sunrise here 6:20 am and sunset 5:35 pm, and that's I think more even than 10 hours,and at summer more hours by the way,,
but as I said I calculate 7 hours to make sure that the sun mostly vertically to the panels , and I can be sure they have good sun shine.
and my batteries are GEL and sealed , I don't think I can use hydrometer also they are brand new.
but what you think ?::::: 3 panels of 200watt each can recharge the 400 amps in aday? putting in mind they are 50% discharged only...
according to my hours time I mentioned? or you think I have to add more panels?

[Sunking]

all items in system new only 2 weeks ago connected. and having sun 8hours ~ 9hours daily , but I calculated as 7 hours when I build my system to be sure.

You do not receive anywhere near 7, 8, or 9 sun hours in a day. Where did you come up with that nonsense? No place on earth receives that much sun. Well maybe here in Panama near the equator at high elevations on a mountain with freezing temps might touch 7 hours 1 or 2 days out of the year. . This is winter months and your Sun Hours are down to 2 or 3 Sun Hours. If you designed at 7, 8, or 9 Sun Hours will fail because that means you only have 1/3 the power you thought and your system will fail. First thing you will notice is your batteries keep getting lower and lower each day until dead because they are never recharged.

You cannot determine SOC by voltage on a working system. Only way to measure SOC on a working system is with a battery hydrometer.

Bottom line is you design for worse case. If you fail to do that, then you planned to fail. You used make believe fantasy numbers.

[SunEagle]

For a 400Ah battery bank you need about 40 amps of charging. Depending on what those 200 watt panels produce and how well they are aimed at the sun will determine you best charging ability.

As for the amount of useful sun hours I seriously doubt you get more than 5 hours so you can forget about any calculations using 7 hours a day.

[zolar]

hi all,,,
having 12v system consist of::: , 2x batteries 12v and 200amh each connected parallel ( means 12v with 400amp output ) charged by.. 1- sun yoba L60 charge controller as 60amp ( its not MPPT but equal to MPPT as written in catalog of the device ), and 3x panels of 200w each. connected parallel also , suppling 600w ( group of lights ), after sunset for about 8hours. all items in system new only 2 weeks ago connected. and having sun 8hours ~ 9hours daily , but I calculated as 7 hours when I build my system to be sure.

the problem is directly after the lights comes on the capacity of the batteries bank drop Significantly from 100% to 85% then keep reducing then Stabilizes at 81% , but after that it goes slowly to 50% for all 8 hours , is it normal or there is something weird .
btw I see the reading in the charger display ,
I am thinking that the charger reading not correct ( I mean either the batteris not fully charged or they are fully charged but the drop not correct ). any comments plz?