# Solar Battery Bank Balance (Discharge 1 bank)

Hi All,

I have 12x 12v 100Ah Batteries (6x 12V + 6x 12v = 6x 24v 100Ah)
Ive had problems recently maintaining a balance and one bank discharges very much
Id like to prevent this

I have all the components required to make some kind of batter balance kit.
such as,

1, a relay board, (will be used to pull a load on the battery with the higher voltage / use a 2nd charger on the bank with the least voltage) what ever…

2, I have a few arduino unos.

3, I have a resistor Kit with basically every resistor id need to hook something up.
dc-dc voltage controllers to run the arduino at 5v from the 24v batteries

anyways,
with respects to code.
I dont know where to start. is there any guides here you would recommend or perhaps help me to make a new code.

Id imagine I would want to use a resistor on the voltage outputs on the batteries to analog inputs.
id want to calculate the voltages into something arduino would find useful
id want arduino to digital write a pin to switch on a relay board when battery a battery is low.
i am thinking it would need to be some kind of compare between battery A and B.
and to turn one of 2 digital Output pins on.

thanks
Shaun

Am I correct to think that you have two groups of batteries. Each group has 6 x 12v x 100Ah batteries wired in parallel. In that case that group of batteries has a total of 12v x 600Ah and, if the two groups are connected in series you will have 24v x 600Ah.

If you are only drawing power at 24v and if one group of batteries is discharging more quickly then I reckon you have at least one faulty or worn-out battery in the group and IMHO the only solution is to replace it/them.

The Battery University website has a lot of useful information about all different battery types.

…R

toxsickcity: with respects to code. I dont know where to start.

Start with some sort of schematic capture software which you'd use to make a drawing of the current system configuration and perhaps your ideas on how to make it controllable. Only then is there much chance of getting meaningful advice on how to modify the system and how to control it.

Hi toxsickcity,

Would this be simular to what you are describing?

We need to at least know this much.

Daz

...R

Sorry first attempt, was from the HDD, will rectify.

(Quick edit: done thanks for the link) DAZ

Hi,
Are your batteries ALL the same age, type(manufacturer)?

What is your load current and what gauge wire are you using to connect the batteries?

Can you post a picture of your battery bank?

What type of battery are they?

If your batteries are “wet lead acid” do you do “equalisation” charge periods?

Tom…

And from the questioner, silence!

I guess they figured it out.

Daz

Sorry everyone,

I have been away, thanks for all the replies.

-Same brand/model/age
-bank de-equalization happens maybe 2-3 times a year, just I forget it and have a blackout for a night
-Battery are maintenance free deep cycle
-Charging source is approx 1500Watts of solar. (50-60Amps)
-I dont equalize as it over voltage my inverter... I might consider this for solo battery health as each cell gets an equalization.. might meaning disable inverter for a day when this happens.. not really doing this tho.

I have an image of how my batteries are wired together for 24v

replacing the batteries is an option, but Id rather not! as it's time consuming and expensive.

I am sure a simple charge balancer will help prolong the life of the batteries also.

MY ARDUINO PROJECT PHOTO,
so the plan is layed out in block form.

My main concern is how to power the arduino. I would like to via the batteries.
but external power source is possible and fine..
Most important would be getting arduino to read two analog inputs as voltage and might mean using the Grey rail as ground and Neg/Pos of the 24v for each 12v.. esentially making one of the analog inputs a -12V (Negative)

apart from that, I will use a relay board to turn on a relay with a light or other load / or additional charge from a solar panel and the arduino will decide which battery needs it.

Thinks I am unsure of, can arduino analog in take a Negative voltage?

the code would be an if statement, such as if analog 1 is higher when analog 2, then turn relay 2 on. else turn relay 1 on.

something like that.

but I dont know the important stuff like, do I need to calculate the incoming analog? what resistor would I need to use if arduino cannot read 12v.. I think it reads upto 5v? meaning I need to drop voltage with a resistor.

thanks everyone for interest in helping me.

cheers

toxsickcity: Sorry everyone,

I have been away, thanks for all the replies.

-Same brand/model/age -bank de-equalization happens maybe 2-3 times a year, just I forget it and have a blackout for a night :( -Battery are maintenance free deep cycle -Charging source is approx 1500Watts of solar. (50-60Amps) -I dont equalize as it over voltage my inverter... I might consider this for solo battery health as each cell gets an equalization.. might meaning disable inverter for a day when this happens.. not really doing this tho.

I have an image of how my batteries are wired together for 24v

replacing the batteries is an option, but Id rather not! as it's time consuming and expensive.

I am sure a simple charge balancer will help prolong the life of the batteries also.

You are missing one essential item of information. What is causing the two sets of batteries to be discharged unevenly.

Also, post a diagram showing the solar panel circuit that normally charges the batteries.

I suspect it would be better to use pairs of 12v batteries to make 6 x 24v batteries and then connect the 24v batteries together as in @Daz1712's diagram (and now, also in @TomGeorge's next Reply), rather than create two huge 12v batteries and then connect them together.

I also remain of the view that some of your batteries will need to be replaced as they have been over-used relative to others. And adding a few new batteries into a large group of used batteries will probably shorten the life of the new batteries making the whole problem expensive to solve.

...R

Hi,
Your connection arrangement is not ideal for your situation, you haven’t said what gauge wire you are using to interconnect the batteries but your daisy chain will not help the situation.

You have to realise you have current to charge your batteries, not voltage, so making sure the current flows somewhat evenly is essential with a system like yours that is capable of 50A charging to a large battery bank.

If in your setup you had 0.2V drop from battery to battery, 5 links = 1V difference between the one connected to the PV/load end and the battery furthest away, when charging or discharging that will have an effect.

This is arrangement will give a more even current distribution.

Have you measured the voltage difference across your links when high current is flowing.
When did you last service/clean your terminals/wiring?

Tom…

Hi Tom George

I have had to place my batteries as is due to space being a factor..

The two banks of (6x 12v batteries) are wired with thick heavy heavy duty welding wire

The two banks sit side by side I've only got 1 wire linking the two banks I might make additional wire and make it as if battery 1 on bank A and B are connected and battery 6 on bank A and B are connected. Essentially what you have drawn above..

Anyways. I don't want to spend money on batteries and batteries would be 3 yr old or so.

I just want to build the kit.

So can I get some assistance with coding. I'd also like to know if Arduino would accept one of the analog inputs being a negative value

I will start researching other projects with similar Arduino uses and see what I need to do

toxsickcity: Anyways. I don't want to spend money on batteries and batteries would be 3 yr old or so.

I just want to build the kit.

I understand that you don't want to spend money on batteries - which of us does?

However IMHO there is no simple fix that takes the form of building a kit.

If the batteries are 3 years old you may well be near the end of their lives. How many amp hrs have flowed in and out of the batteries during those 3 years?

If you re-wire your battery bands as @TomGeorge has suggested you may get a bit more life from them.

I get about 4 years from my lead-acid batteries with a lot of care.

...R

its in interesting concept none the less.

I have seen battery balancer on aliexpress for about \$35
thats cheap but i think it's discharge is around 0.5A which is very little for a 600A bank!

Id like a little more control over this, would be good instead of wasting the energy by loading, the idea can be reversed and add charge to the lowest bank.

I have just came up with a way negative voltages wont happen..

it means the arduino can be powered by the banks ob batteries too.

Dc-Dc converters always usually have common grounds which works well for the diagram I uploaded now

I'd need to divide the 0-1023 by 30V

Quality batteries should give a good 5-7 Years
My batteries are not sitting on the floor. they are raised a little too to prevent the bottoms of batteries holding a thermal difference, Ive read a lot on batteries.. and things such as a full DOD even once can F them for good... not good at all,

So the idea to build a arduino project that others will able to follow, can build an alarm into it even.. some sort of detection..
buying two volt meters is also another way to seeing.. but automated always seems better!

toxsickcity: Quality batteries should give a good 5-7 Years

That depends on how many amp-hrs are passed in and out of them, and how they are maintained. As you do not seem to have had an optimal wiring system my guess is that some of your batteries are now in poor condition.

What specific batteries do you have?

To my mind you are chasing a Will-o'-the-wisp.

...R

I came for support to build a project.

looks like I will just trial and error this bastard into submission

thanks for all the concerns.. Im happy with my setup. it works for me.. well kind of..

It does not end here as there are others out here.

Claims on wireing and what the incorrect wire can do can be right but i would not be making statements unless i could see and do testing myself.

The comany a worked for ran a 12 volt 4400 Ah backup supply that would supply 500 amps continuous from a 3 phase power supply and 2 banks of 2 volt 2200 Ah cells and yes they were big! Each cell measured half a meter square and stood almost a meter tall, there were of course 12 of them and they were wired series parallel with the connections to the controller off one end as per instructions from the company. It worked! The wires were almost 20mm of copper.

We all know that there are optimal ways of wireing but physical space does not always comply with the theory of optimal.

Enough of that.

In reguards to your question, i am currently working on a system to go in my car (much less nerve racking than the thought of shorting a system capable of delivering 1000 amps ar 13.8 volts for 30 minutes). It will be set up to run my car fridge and other electronics off the main car battery and a jumpstart pack which it will switch the load to before the main battery gets to low.

Any how i have looked at how to monitor the voltage on both batteries as well as amperage in and out of both. I wanted to use the Arduino to control and store data but how? when the batteries operate between 0 and 16 volts. I want to display voltage to two decimal points but the 1024 steps of the a to d dont give that resolution. Then i realised that anything below 10 volts is useless to me! Yay the good old Zenar! Working on a voltage swing of 10 to 18 volts and using an 8.2 volt zenar inline to drop my voltage followed by a voltage divider of 2K7 and 2K2 ohms gave me a voltage swing of 0.8 to 4.4 volts, purfect for the Arduino 5 volt input.

So by using the above and setting up another to handle 24 volts you can now monitor the two banks and set off an alarm if an inbalance occurs.

And yes i know the above COULD have ways of going wrong (lets face it Adruinos are cheap) but i did say i was working on it and it does not involve op amps masive voltage dividers or optocouplers.

Using a cheap boost/buck converter from ebay to run the Arduino off the battery bank is not hard.

Once in place you can start looking at more data and narrow down the faulty units, it will at least cut the problem in half.

Please dont set up a system that discharges the higher bank that seems wasteful. Look at the way they do lithium cells in a pack this could be used for your system as well.

Still if you have cells that are not at full capacity (a speculation not a fact at this time) then the string will only run at the lowest capacity.

Could you tell me what is the largest current draw and how long it would go for?

Hope this gives more to think on and wait for more questions.

Daz

Hi,
This will would be the easiest to measure your banks voltages, using some simple maths to get the top bank's voltage level.

It will identify which bank is lower, but not if it is only one battery in the bank.

Sealed batteries unfortunately do not make individual battery condition easy to establish.
Wet cells of course, all you need is a hydrometer.

You need to find the suspect batteries not try and discharge or charge a complete bank.

If you have a DC clamp meter you can check your link currents, with the banks completely unloaded and with no charging.

Checking the current in each link will tell you where your suspect batteries maybe, the current will be flowing into them and dragging the good ones down.

However if you have a battery with high series resistance, then an individual load test is probably another alternative.

Tom.....

TomGeorge:
Hi,
This will would be the easiest to measure your banks voltages, using some simple maths to get the top bank's voltage level.

It will identify which bank is lower, but not if it is only one battery in the bank.

Sealed batteries unfortunately do not make individual battery condition easy to establish.
Wet cells of course, all you need is a hydrometer.

You need to find the suspect batteries not try and discharge or charge a complete bank.

If you have a DC clamp meter you can check your link currents, with the banks completely unloaded and with no charging.

Checking the current in each link will tell you where your suspect batteries maybe, the current will be flowing into them and dragging the good ones down.

However if you have a battery with high series resistance, then an individual load test is probably another alternative.

Tom.....

Um tom, is that an Arduino? Are you running 24v direct into A1?

Daz

toxsickcity: thanks for all the concerns.. Im happy with my setup. it works for me.. well kind of..

Assuming that the problem has arisen because you have all the 12v batteries in a parallel row on each side and only joined in series at the ends, then it may be worth reversing the order of the 12v batteries in each row so that the ones at the tail are now at the front, so to speak. The batteries that are presently at the tail are likely to have been used a little less.

...R