Mix Matching LiFePO4 Batteries

[SolarAntics]

OK, and why the three separate bus bars?

Brain wanted to keep the groups separate to their own bars for some reason:

This better?

 

[SomethingAppropriate]

Better? If at least I don't get to successfully create a design here, I would like to at least get some theoretical discussion and knowledge here. All these condescending comments are the opposite of constructive. Like what is the point of a forum? To help teach, learn and grow a scientific community, or to restrict the attainment of knowledge and development? I say humbly.. I am very new to this, and wasn't BORN with the knowledge of electrical engineering. Funny thing about knowledge, is your aren't born with it; so everything you know, you learned at some point.

I would not go to a forum and ask how to construct a house. There are far too many details to cover. It also takes time to understand things>
I speak for my self in saying; Learning is about making THOUSANDS of mistakes. That is how I learn.

We are trying to help you not burn your house down.

 

[SolarAntics]

I

Oh, and unfortunately, in a public forum, everybody can comment, ya have to weed through the trolls and seek out the teaching information...

Reporting posts that simply insult or goad you is what moderation tries to fix, but bad apples happen.

A thick skin is often needed to glean info in forums.

You sound like a very good moderator, and I am very happy that you have joined in on my thread. This community seems very intelligent and helpful. Everyone can have their snarky and arrogant side, and I get that when you get to the upper levels of the scientific community because you start dealing with theoretics pushing the boundaries of what the book says to advance science. So there is a certain air to that level of forum and sometime people forget how to treat the plebeians / newbies such as my self. I'm adult enough to have a conversation about shitty and deconstructive attitude. I'm no angel and have made my fair share of demeaning comments before that I regret; having failed to put the 1 million foot view into perspective. Anyhow. Water under the bridge and I am sure we are all on the same page and in agreement here. Thick skin, like body armor always breaks at some point when hit over and over again, so foster a healthy community of values, principles, and liberties. Thank you again and nice to make your acquaintance.

 

[SolarAntics]

I would not go to a forum and ask how to construct a house. There are far too many details to cover. It also takes time to understand things>
I speak for my self in saying; Learning is about making THOUSANDS of mistakes. That is how I learn.

We are trying to help you not burn your house down.

I know you are, that is why I am here. Just had to test the forums fortitude with a snarky comment of my own. Thank you from the bottom of my heart for your help and guidance!

 

[SomethingAppropriate]

Brain wanted to keep the groups separate to their own bars for some reason:

This better?
View attachment 253585

This is what you want. But again, I dont understand why you dont just get a 24/48v batttery and inverter/charger

If your 12v system has an AC charger, just connect that to your new 24v system.
You would only have to have solar connected to the 24v system in this case.

Is this a house? An Rv? Shed?

As Supervstech mentioned

We certainly could use specific models of your equipment.

 

[SolarAntics]

I meant wxactly what do you have?

Not just batteries, what inverter do you have?

What are you planning to load on it?

For my RV

A 24v 2500w pure sine wave inverter by VEVOR
\_ Most draw at one time would be the microwave/air fryer that pulls 1700w plus the RV lighting, water pump, some draw for the water heater startup, and a 45amp 120vac rv converter to charge and maintain an independent 100ah lifepo4. I will likely be adding a 12v fridge that would pull 60w (will plug into 120vac).

 

[robbob2112]

Brain wanted to keep the groups separate to their own bars for some reason:

This better?
View attachment 253585

This has 4 bus bars in it, would be better to just get a 12 position pure copper set from signature solar and have enough room to put everything on its own post.

600A 12 Stud Busbars | Red & Black Kit

Manage high-current electrical connections efficiently with the 600A 12 Stud Busbars in a Red & Black Kit, ensuring organized and reliable power distribution in your electrical setup.

signaturesolar.com

 

[SolarAntics]

This is what you want. But again, I dont understand why you dont just get a 24/48v batttery and inverter/charger

If your 12v system has an AC charger, just connect that to your new 24v system.
You would only have to have solar connected to the 24v system in this case.

Is this a house? An Rv? Shed?

As Supervstech mentioned

We certainly could use specific models of your equipment.

Financial constraints to answer your first question.

MPPT 24v charger is from LiTime rated at 30a output and 100v max input >> Connected to 800w total of solar (two 400w arrays in parallel (each - OCV=47.2v SCC=11a))

The 120vac charger (LiTime 29.2v 40a) is isolated for charging by means of a generator for emergencies only.

I will cut the solar charger off to batteries using a switch when not connecting solar panels and/or using the generator (panels will be disconnected anyways). The 120vac charger goes to an outlet facing outside my rv (again to reiterate, this is completely isolated from any other system) to connect my generator to.

 

[SolarAntics]

This is what you want. But again, I dont understand why you dont just get a 24/48v batttery and inverter/charger

If your 12v system has an AC charger, just connect that to your new 24v system.
You would only have to have solar connected to the 24v system in this case.

Is this a house? An Rv? Shed?

As Supervstech mentioned

We certainly could use specific models of your equipment.

I am stuck with the 4 12v batteries, and am now thinking of using a 24v instead of two additional 12v in series for that 3rd pairing. Same cost for a 24v 100ah as it is 2 12v 100ah and a balancer. I wish I had known about balancing series before buying the 12v batteries. Should have really planned for a 48v system instead. I live and learn. Thanks for your help! I will get a new schematic up soon.

 

[SolarAntics]

Thinking buying a 24v battery is going to be easiest and not much more money considering costs of balancer, cabling, and space. Unfortunately I am stuck with the Brand B and C 12v batteries.

 

[wpns]

Thinking buying a 24v battery is going to be easiest and not much more money considering costs of balancer, cabling, and space. Unfortunately I am stuck with the Brand B and C 12v batteries.
View attachment 253616

That's better. Too many bus bars, but better.

 

[SolarAntics]

That's better. Too many bus bars, but better.

The theory I have is that the bus bars connecting all the 100ah batteries together is to create a capacity group close to the 180ah capacity group. My understanding is that you want capacities very close when connecting in parallel? So the bus bars will separate the 180ah group from the 200ah group. So we have 200ah bus bars connecting to the final distribution bars, that the 180ah group connect into as well complete a parallel connection of a 180ah system and a 200ah system. Is this logical?


180ah ---v____ 380ah total
200ah ---^

Instead of:

180ah ---v
100ah --<>--- 380ah total (but again now hooking up very different capacities in parallel.
100ah ---^

 

[Mattb4]

... My understanding is that you want capacities very close when connecting in parallel? ...

Does not matter all that much.

 

[SolarAntics]

I just wanted to express a huge amount of gratitude to all of you guiding me here. It has been an incredibly productive and educational weekend. Your frustration, hard work, and patience with me here, in best efforts to steer me true, is seen and immensely appreciated!! God bless you all!!

 

[SolarAntics]

Does not matter all that much.

I thought charge and discharge rates is a major factor here.

Great videos, thank you

There are definitely limitations in this extreme of a set up between a 5ah bank limited to 3a max in (BMS fluttering like crazy) and overall current potential reduced to the 304ah bank which probably can handle much more than the attempted 21a. Very interesting to see the eddy current in action. I still think it is a very good idea to try and match the capacities as much as possible to get the most efficient charge and discharge currents available. Logical?

Also to note the charge voltage curve... - Upon further consideration, I don't think this matters as that the groups should be at the same voltage the whole time.

 

[Supervstech]

Keep in mind, the fewer connections you have between the batteries and the load, the better.

 

[Horsefly]

I just wanted to express a huge amount of gratitude to all of you guiding me here.

I will say you have come a long way in a short time. The first few diagrams you posted included (as you now know) direct short circuits across all three batteries that would have caused a very nasty / expensive surprise. Now you seem to have got it. As others have said, get all three of you 24V batteries (two of which are built from a couple of 12V batteries) on one pair of bus bars.

I don't enough about the cross-battery balancers to have much of an opinion, but I wouldn't count on them to help much.

 

[Ectropian]

I’m interested to know how the latest build is doing for you? I currently have 2x12v 200ah batteries in series and am in the process of adding a 24v 200ah battery in parallel. Is the balancing working well with your system and how necessary do you think the balancer is?

I currently have 2 MPPT controllers bringing the PV load into the bus bars.

 

[SolarAntics]

I’m interested to know how the latest build is doing for you? I currently have 2x12v 200ah batteries in series and am in the process of adding a 24v 200ah battery in parallel. Is the balancing working well with your system and how necessary do you think the balancer is?

I currently have 2 MPPT controllers bringing the PV load into the bus bars.

It's on a bit of a hold due to weather - Here is a link to my project page though - https://diysolarforum.com/threads/m...kw-lifepo4-2500w-inverter.95256/#post-1283870