16 * 200ah lead-acid array voltage difference

Thread Starter

Fhorst

Joined Aug 16, 2019
15
Hello all,

I have 4*4 12 Volt 200Ah deep cycle batteries.

Configuration is the standard, 4* parallel and 4* series to get 48 Volts array.

Left up is negative right down the positive connection.

So far, so good.

During discharge the first batteries discharge the most.
The one that have the negative connection and the one that have the positive connection.

While the middle batteries still have 12.4 volts, the first and last can be as low as 8.5 volts!!

Now I've always learned that lead acid below 10.5 volts is a dead battery.
Not able to recover, need to replace.

When I disconnect the load, slowly the voltage is rising, up to 10.5 and higher in time.

If I wait several hours, it's turns out to be about 12 volts, officially nothing to worry about.

But still....
8.5 volts??
That doesn't seem right to me.

It is not difficult to have the leads from the 4 connect to one point, not Daisy chain.

That would be more balanced discharge, as 4 batteries are used at the same time
(4 at the negative connection, 4 at the positive connection, and the 8 in the middle)

It have to do with resistance, as the first connection have the lowest resistance, that one gets the heavy load.

So, why do all the lead - acid setups advise to Daisy chain and make the connection to one battery and not all 4 at the same time?

(Cables need to have the same length to get the same resistance, so all are charged/discharged at the same time)

I can't understand why I should abuse the first connection batteries.

If someone could explain why it is a good idea to daisy chain instead of star, please inform me!!

The batteries are charged with solar panels, normally enough to have them fully charged at noon again.

Having the 8.5 volt reading worries me!
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
Lol.
How does that comments help?

"Stuffed"
Stuffed with cotton?
Like pluche bear?
Lol

If you want to contribute, please answer the question I ask.

Why daisy chain and not star?
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
some of your batteries are stuffed ...
Fyi,
The batteries are "new", about 6 months old.
Never have been discharged below 20%.
Streight from the warehouse, production date was a month before I receive them.

While Thailand can be hot, the batteries never went over 38 degrees (and that was a short time)

Stuffed, as in old...
Not really possible.

And without accurate measurement, you must be psychic medium to see from far :)

Specific gravity is within normal range, load test works just fine.

It is "normal" behaviour that the first connection batteries have lower voltage.

I can't understand why people like to abuse the first connection if they can share the discharge over 4 connections.

Yet, that is the "normal" setup.
Daisy chain parallel and daisy chain serial.
With one connection in, and one connection out.

Why?
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
I understand for the parallel, that makes sense.
It also makes the 12 Volt go to 48 Volts.

But the series to 4 x 200 ah@48 volt...
That puzzles me.

As the first connection is at only one negative pole,who then daisy chain down to the other 3 rows.

And The same on the positive connection, not the same row as the negative connection, it is connected to the 4th row, last positive pole.

As result the first negative and the first positive connection gets the biggest beating during charge and discharge.

Result during load (not even high load, about 500 watts)
The first batteries measures way below the minimum 10.5 volts.

I am aware that measuring wet batteries under load does not give accurate information.

Still 8.5 volts..
That's low.

Going down the daisy chain Voltage go up, next is 11 then 12 and 12.5 (roughly)

Let the array rest (no charge, no discharge) for several hours, it stabilise to about 12 volts per battery. (= 30-40% charged)

If I would connect in a star the discharge would be split between the 4 rows, more even then a daisy chain does.

It does costs little more cable.

Fyi, batteries are connected with 35mm2 cables, all even long/short (+/- 20cm)
and the cables to the inverter/charger are 50mm2. About 2 meters)

lead poles are clean, so are the copper connections.
 

Orson_Cart

Joined Jan 1, 2020
11
Your: "
Specific gravity is within normal range, load test works just fine.

It is "normal" behaviour that the first connection batteries have lower voltage.

I can't understand why people like to abuse the first connection if they can share the discharge over 4 connections.

Yet, that is the "normal" setup. "

does not make sense - are you implying people ( others ) always use the lowest 12V paralleled string?
- if this is a the case you have no control over the discharge - why then be surprised that they are the flattest?

also you did not answer my qu about proper 4 x 4 connection ...
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
"not last long" is relative term.
Yes, life span is shorter.
Not many countries around the globe have 24/7 temperature between 15 and 25 degrees.

Colder and hotter reduce lifetime.

4*4 is not that difficult.

4 x 4 12v 200ah batteries make a 48v 200ah battery

If I would have only 4, I have no other option for positive and negative pole connection.

If I have 8 batteries, 2 strings of 4.
I have options.
I can connect both negative as a split (star) and both positive as a split (star) or daisy chain.
Have the first row connect to the second row.
Both positive and negative the same length cable.

Then, connect the positive to the first string, and the negative to the second string.

With 3, 4, 5, 10 rows it stays the same, only more layer.

The battery that is the first connection in the array apparently receive the heavy beating, as after load, that battery have the lowest Voltage.

If it would be a star, with 10 rows the star have 10 legs.
All ten "first" battery have the same lower voltage.

Except this voltage is a lot less different from the rest of the batteries in the array.

Under load, with one pole, I have readings as low as 8.5 volts.
It will stabilise when the load is removed.

But still...
How does daisy chain provide more control?
 

Orson_Cart

Joined Jan 1, 2020
11
you have not answered:
"does not make sense - are you implying people ( others ) always use the lowest 12V paralleled string?
- if this is a the case you have no control over the discharge - why then be surprised that they are the flattest? "
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
No, sorry, I think I'm explain wrong.

4* 12 = 48 Volts.
A full battery is 12.75 volt.
4* 12.75 = 51 volt fully charged.

When I measure every single battery, all give 12.75 volt.

During discharge, this changes.
The first and last battery, when measuring one battery (not the string) will be lower voltage then the 2 in the middle.

After discharge, they equalise and return to 12.5 volt per battery, total 50 volts. (In a few hours)

"Direct" after the discharge, the total voltage is 50 volts, only per battery there are differences.

Extend this situation with more strings.
Not one row of 4 batteries provide 51 volt (fully charged)
But 3, 4, 10 what you like :)

The Voltage stays 51 volt.
Ah increase with every string added.

The strings are Daisy chained, positive to positive, negative to negative.
Can go as many as you like.
Voltage stays 51 volts.

For charging and discharging one line is connected to the negative and one to the positive.
(See picture of 3 batteries, only one I could find)
You get the idea.

In this picture the first and last will have more discharge .
Adding more strings doesn't change this.
But it does increase the total capacity of the array.
More total capacity is higher discharge possible without reduce the discharge rating (normally per 20 hours)

With higher discharge, the first batteries in the string discharge the most, as I can measure even down to 8.5 volt on that battery.
Total voltage is still around the 48-50 volts, the total array have no problems.

But that first battery.
That reading.
Is it "nonsense" or real voltage of that battery at that time?

If discharge stops, and it have several hours then all individual batteries are again 12 - 12.5 volts.

The alternative I talk about ,the "star" apparently is used with battery balance system?

(See picture)
 

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Orson_Cart

Joined Jan 1, 2020
11
respectfully, nothing you have descibed is a 4 x 4 battery connection - nor have you answered the qu about the lower 4 x 12V parallel section being drained most often ...
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
Ok,

Please tell me What you think a 4*4 battery is.

For me it is 4 times a 12 Volt battery to make 48 Volts
And 4 times 200ah to make 800ah.

We agree that there are 16 X 12 Volt battery.

Nagetive
(-) 12+12+12+12
12+12+12+12
12+12+12+12
12+12+12+12 (+)
positive

When I drain due load the batteries look like
Negative
(-)8.5+11.5+11.5+12
11+12+12+12
11.5+12+12+11
12+11.5+11.5+8.5 (+) positive

After a few hours the battery array look like

(-) 11.8+11.8+11.8+11.8
11.8+11.8+11.8+11.8
11.8+11.8+11.8+11.8
11.8+11.8+11.8+11.8 (+)

You get the idea.

Center batteries are still at 12
First + and - are low, next one in line little higher.
 

Orson_Cart

Joined Jan 1, 2020
11
you are not paralleling the strings properly, put 4 x 12V in parallel, do this 4 times, put the 4 lots of 12V in series to get 48V ( 54V float )
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
48 volt at 800ah.

Go left or right.
4 x 800ah (12v)= 48v@800ah
or
4 x 200ah (48v)@= 48v@800ah

in theory it even can be combined, but I don't see anyone doing this.

i tried a string to connect to the lower string.
(Not thick cable, just to test if it would short anything)

seems to be working.
(-) |12+12+12+12|
| | | | |
|12+12+12+12|(+)
The | is wire connection between the batteries

The star is like the use of busbar.

(-)12+12+12+12(+)
(-)12+12+12+12(+)
(-)12+12+12+12(+)
(-)12+12+12+12(+)

Setup now is

(-)| 12+12+12+12 |
| 12+12+12+12 |
| 12+12+12+12 |
| 12+12+12+12 |(+)

Where | the connection between the rows is
 

Thread Starter

Fhorst

Joined Aug 16, 2019
15
If I understand you correctly, the mostly suggested setup, making to de desired voltage, and then the amperage is wrong.
This picture 3*3
3* 12 to 36, the 36 to ?? Ah.

The lines I drew are making first the ??ah and then the 36 volt.

Interesting.

Why?

As most of all the examples of installations first go to the Voltage, then the amperage.

Not first the amperage then the voltage.

Never too old to learn.

Why??
 

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Thread Starter

Fhorst

Joined Aug 16, 2019
15
In theory you could add the yellow lines.

Making the amp and voltage increase at the same time.

And make use of same length cable to connect to all 3 (-) and (+) at the same time.

Schematic diagram looks like it would share the load (charge and discharge) the most equal on all batteries.

Real life?
I don't know.
 

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Thread Starter

Fhorst

Joined Aug 16, 2019
15
I am looking to buy a battery balancer.

I've seen some reviews on YouTube, people are quite impressed on how they work.

I'll need to ask if every row needs its own balancer, or if it could do 16 at the time :)
 

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