I am talking to a friend which has 10 strings of solar panels.
Each string delivers around 12 Ampere @ 650 Volts.

These are connected to a DC bus and go from there to frequency drives where the DC is being converted into 3 phase AC 480V.
Usable DC fluctuates from around 500VDC to 850VDC.

The idea is to have a battery bank directly connected to the DC bus.
166 pcs LFP batteries @3.6V = 600V and @3.0V = 500V

with the use of 11pcs JK-BMS 16S we could disengage the batteries below 500V and above 600V
In theory the BMS's should be enough to control this function?
I was also thinking about using a microcontroller and a high voltage DC/DC solid state relay to connect and diconnect the battery.

 

You need an MPPT controller.
At a guess, 850V is the open circuit voltage, so the peak power will occur at 722V. Without an MPPT the output will get clamped at the battery voltage (600V) so you will lose the difference, which is about 17% of available power.
The peak power voltage varies with temperature at about 0.3%/°C, so at 75°C it will be well matched to the battery, but not if the temperature is cooler.

 

hi thank you @Ian0 But no we don't need nor want an MPPT controller, as described we are not going to use one.
We want to make it work as described. we are in the dominican republic (temperature), no MPPT needed / wanted.

Not sure what VOC is, 850V is also under load, not sure though at what condition / load.

 

hi thank you @Ian0 But no we don't need nor want an MPPT controller, as described we are not going to use one.
We want to make it work as described. we are in the dominican republic (temperature), no MPPT needed / wanted.

Not sure what VOC is, 850V is also under load, not sure though at what condition / load.

It won't work very well.

 

To safely charge any sort of batteries you will need a battery charging circuit to control the current . Battery charging with no control over the current can damage most types of batteries and will certainly reduce the useful life of batteries as well. It can also cause fires and explosions.
So while getting the maximum efficiency is not a priority, safety should be a priority. Thus you will require a battery charge control scheme with a battery charging regulator.
So what you need to know is what the charging current and voltage requirements are for the batteries that you intend to use will be. When we know that requirement we will be able to create the design of a suitable charging control system.

 

Battery charging with no control over the current can damage most types of batteries

The TS did say they were planning on using a JK-BMS which will handle charging, balancing and monitoring. To quote the JK website: "The device features precise cell voltage monitoring, temperature sensing, and real-time current measurement to ensure optimal battery performance and longevity. It incorporates advanced balancing algorithms that maintain cell voltage equilibrium, preventing overcharging and extending battery life. The system includes built-in Bluetooth connectivity, allowing users to monitor battery status and adjust parameters through a dedicated mobile application. With its robust protection mechanisms, including overcurrent, overvoltage, undervoltage, and short circuit protection, the JK BMS 16S 48V 200A ensures safe operation in various conditions. The system's compact design and efficient heat dissipation make it suitable for electric vehicles, solar energy storage systems, and industrial applications."

I've not used their products or endorse them (preferred to roll my own), but they do have a good reputation. Also LFP cells are much more robust and safer than LiPo or LI-ion cells, they will take a lot of abuse with minimal damage and won't catch fire or explode.

 

OK, it seems that I missed the part about including a battery management system.
So my comments about the need are valid, but not applicable. The fact is that I am not familiar with the "JK-BMS" and so unable to comment as to how suitable it would be for the application.

BUT, "The idea is to have a battery bank directly connected to the DC bus. 166 pcs LFP batteries @3.6V = 600V and @3.0V = 500V" as a plan still requires a scheme to avoid both excessive charging current as well as charging over-voltage when the batteries have reached full charge. ALSO, it is important to avoid an excessive discharge.
Consider that the power levels of the system here are able to cause a lot of damage if "things go wrong", the project is no place for experimenting.

 

BUMP

Let's try to go from all the "it doesn't work"-negativity back to looking into the challenge.
I am looking for productive brain activity

 

The basic math does not work. How do you get a 650V battery from 11 48V controllers?

11 x 48 = 528

 

BUMP

Let's try to go from all the "it doesn't work"-negativity back to looking into the challenge.
I am looking for productive brain activity

My professional "brain activity" sends a warning that such power levels, any small errors are dealt with in a most unforgiving manner.

 

The basic math does not work. How do you get a 650V battery from 11 48V controllers?

11 x 48 = 528

This is for people that understand the math of LFP / LiFePo4 batteries.
you are welcome to join my post again once you have done your homework.
Until then please do us a favor and stay away, you are not contributing anything, you are just hindering with your lack of knowledge.

My professional "brain activity" sends a warning that such power levels, any small errors are dealt with in a most unforgiving manner.

Please read the original post again. Nowhere does it say "looking for a safety officers brain activity".

Please contribute in a positive way, if you are even capable, otherwise look for a post where a safety officer is required.

I am not looking for a safety officers brain incapacity.

Thank you to everyone for understanding.

BUMP, let's try again

Only positive people are allowed to post from now on.

 

This is for people that understand the math of LFP / LiFePo4 batteries.

Math is math, it does not change with what you apply it to or what you opinion is. And yes, I do understand LiFePo4 cells. They have a maximum voltage to 3.65V when fully charged, which drops almost instantly to 3.2V when discharging.

A 48V LiFePo4 batteries is 15 cells, which is 48 x 3.2. When fully charged, it is 3.64 x 15 which is 54.75V. 11 of those are 602.25V. And, like the individual cells, it will drop to 528V for most if its useful life.

You mentioned 166 cells, which comes out to 605.9V. That is not a multiple if 15, so you cannot use 48V charge controllers to make your battery.

If you cannot do grade school math, I suggest you take you take up different hobby.

Ih, and you do not get to say who posts.

 

OK, so the TS is offended when I offer a caution, which was not intended to be negative at all. Likewise the cautions about avoiding overcharging. NONE of that was intended to be at all negative. In my profession I was legally obligated to point out hazards to people. No where was I saying that any of the ideas would not work.

BUT, since you do not want any advice, YOU WILL NOT GET ANY MORE ADVICE.

 

so you cannot use 48V charge controllers to make your battery.

but what charge controllers are you refering to?
(please don't answer )

In my profession I was
legally obligated to point out hazards to people.

this is not about your profession. please read the post.
I would appreciate it.
No question has been asked about hazard advise.


I appreciate people helping me, but I am not interested in your previous life nor job.
You probably should be on a dating site and try to get attention there?
This is about a 600V LFP battery.

BUT, since you do not want any advice, YOU WILL NOT GET ANY MORE ADVICE.

not about hazards, this is about a 602.325728301V LFP battery.
thank you, I appreciate it.

 

This is about a 600V LFP battery.

So that explains why is says 625 Volt LiFePo4 LFP Battery in the title?

 

You seem to have failed to grasp some of the major concepts about solar panels, and are then getting angry when the experts point out your lack of knowledge. The output is a constant current source with the current dependent on the amount of light falling on the panel, so the voltage measured on the output will vary, but it varies with the load.

If you connect the output from solar panels to a battery, the battery will stabilise the output voltage.

By "frequency drive" do you mean a Variable frequency drive? They are for driving motors, and they normally take a single or 3-phase AC input, and would soon shut down with an error message if given a randomly varying DC input, so I'm presuming that what you have is actually a grid-tied solar inverter. You were not too specific about what this device was: probably you don't know what it does.

If I am correct about what it is, then supplying it from a battery is a really bad idea, because it is an MPPT controller (you know, the thing that you refuse to use) and its job is to extract the maximum power from the source. Attempting to extract the maximum power from a battery is probably not such a good idea.

 

not about hazards, this is about a 602.325728301V LFP battery.
thank you, I appreciate it.

Welcome to AAC.

I'm afraid you are mistaken.

Unlike a search engine or an AI agent, AAC involves transactions between human beings. Because of this, when you post questions to the forums, you may find you get answers that you don't expect—but this doesn't mean they are off-topic.

You came here to take advantage of the expertise of the members, there would be no other reason to post your questions here. In the process you will find that you may also get corrections or additions to your question, or even to the project that provoked the question.

This is particularly true for issues of health and safety since not only do we have reasons to be careful providing advice that could lead to injury or even death, but one here wants to imagine another member suffering such a fate,

So, when potentially dangerous project is described, and the expertise and experience of the poster is unknown, there is a legitimate impulse to warn (or remind) the poster about the danger,

This is intensified when the post(s) suggest a naive approach, or specific gaps in knowledge since these things multiply the risk inviolved.

On a related topic: your attitude that this is all about you, and the rude dismissal of credentialed engineers who go out of their way to provide advice free of charge, is very undesirable and is very likely to render you persona non grata—accompanied by an enforcing ban from AAC.

If you believed this was a place to get free, custom, engineering consultation according to your strict specification of what constitutes "legitimate" advice, you were mistaken about that too.

You are welcome to reconsider your approach and become part of the community—or to leave—but you are not welcome to engage in freelance moderation. The decision is yours.

Again, welcome to AAC—sincerely. Sometimes we get off to a bad start, but restarting is available and I hope you choose that path.

 

For what it's worth, you have the attention of the entire staff on this thread and you, the thread starter.

 

Welcome to AAC.

I'm afraid you are mistaken.

Unlike a search engine or an AI agent, AAC involves transactions between human beings. Because of this, when you post questions to the forums, you may find you get answers that you don't expect—but this doesn't mean they are off-topic.

Thank you Ya’akov. I came here because I was looking for answers that I didn't expect. Those are the ones that I can learn from. But I expect from people that reply to my post to respect the basics of a conversation etiquette.
They have to do a lot of homework, I don't like to be insulted nor disrespected, do you or do you think they do?
They just came here to hijack my post with the subjects that they had in mind without proper reading the basics of my aticipated project.

Only one did.

You came here to take advantage of the expertise of the members, there would be no other reason to post your questions here. In the process you will find that you may also get corrections or additions to your question, or even to the project that provoked the question.

To be entitled to a correction you should have read the subject, thought about it and have the required understanding.
I am open to ideas, additions and corrections if it is from people that have read the post, have sufficient knowledge of the subject and their correction is about the subject. Otherwise just ask me politely and I will explain it to them where they misunderstood something or are lacking fundamental knowledge.

This is particularly true for issues of health and safety since not only do we have reasons to be careful providing advice that could lead to injury or even death, but one here wants to imagine another member suffering such a fate,

So, when potentially dangerous project is described, and the expertise and experience of the poster is unknown, there is a legitimate impulse to warn (or remind) the poster about the danger,

This is intensified when the post(s) suggest a naive approach, or specific gaps in knowledge since these things multiply the risk inviolved.

They are more than welcome to open a post where they inform the entire audience of the forum about the dangers of electricity and point the people towards that thread.. Everyone can then descide for themself whether or not they are lacking knowledge regarding high voltage, and whether or not they want to participate in that subject that differs. I feel that it is rude to hijack someones post.
Start your own.

It is dangerous to connect a 120V AC socket. It is rude to highjack every post that talks about voltage above 12V and for them to throw that in there because that is what they have in mind.
Etiquette of a conversation is to listen and to understand each other.

Every AC socket is a minimum of 120V.
All solar installations are 1000V of 1500V these days.

Yes I can fall down the ladder aloft connecting those panels.
Yes I can fall down the stairs going down to get some tools from the truck.
Yes I can have a deadly accident in the car when I buy the cables not wearing a seatbelt.
...
Don't highjack my post please for things that are important to you but nobody else!

On a related topic: your attitude that this is all about you, and the rude dismissal of credentialed engineers who go out of their way to provide advice free of charge, is very undesirable and is very likely to render you persona non grata—accompanied by an enforcing ban from AAC.

If you believed this was a place to get free, custom, engineering consultation according to your strict specification of what constitutes "legitimate" advice, you were mistaken about that too.

Those credentialed engineers have to learn to read and put some though into the task in question. If you are not capable of doing so you will never become a credentialed engineer. If you don't read the questions and don't put any thought into it but still chose to drop your off-topic subject into and engineers topic that is looking for smart advise, then you are just rude.

Don't highjack every post for the purpouse of improving your forums-ranking. I didn't dismiss the only one engineer here, that has responded so far and that has an understanding, and more important put some thought to it.
I don't respon well to rude people. And yes I initiated this post, and I can expect conversational etiquette. If you want to educate people about dangers of electricity please do so in your own post and send me an invitation to your discussion.
My post was about another subject, please join but show common conversational etiquette and respect.

I have taken your points but only can agree with you on some of them and I will work on them. I don't appreciate your threats though, I don't consider them professional nor good attitude either.

You are welcome to reconsider your approach and become part of the community—or to leave—but you are not welcome to engage in freelance moderation. The decision is yours.

Again, welcome to AAC—sincerely. Sometimes we get off to a bad start, but restarting is available and I hope you choose that path.

I appreciate you expressing your opinion in such a polite manner, but there is nothing wrong in my expectation to receive the basic conversational etiquette here.

 

For what it's worth, you have the attention of the entire staff on this thread and you, the thread starter.

But what is this here? 23,726 posts... I just can't geat my head around this "I post just to have more posts than someone else and very soon 1000000"-thing.
Can you please elaborate on your post?