More than 4 Renogy Smart Lithiums

[sunshinestatestreaming]

Going all out with a Renogy install using 6x100 Ah Smart lithium that renogy said wouldn’t work as it may cause balancing issues, however I am not seeing it yet. Has anyone else tried this and if so how did it work?

 

[MisterSandals]

said wouldn’t work

It definitely won't work if you wire your batteries like that (from the ends of parallel batteries).

 

[Sverige]

It definitely won't work if you wire your batteries like that (from the ends of parallel batteries).

Hogwash. It will work just fine. Those interconnects are so short that at the worst case there might arise a tiny inbalance in SOC between batteries, which will even out as you reach the steeper incline part of the charge or discharge curve.

This superstitious belief that any inbalance in SOC of parallel batteries is somehow dangerous seems only to be held by those who’ve never actually done it.

 

[Pi Curio]

Going all out with a Renogy install using 6x100 Ah Smart lithium that renogy said wouldn’t work as it may cause balancing issues, however I am not seeing it yet. Has anyone else tried this and if so how did it work?

Are all of these in parallel?

If so, why not something similar to this?

Best,
D.

 

[Pi Curio]

Hogwash. It will work just fine. Those interconnects are so short that at the worst case there might arise a tiny inbalance in SOC between batteries, which will even out as you reach the steeper incline part of the charge or discharge curve.

This superstitious belief that any inbalance in SOC of parallel batteries is somehow dangerous seems only to be held by those who’ve never actually done it.

Maybe I'm wrong, but I have a feeling you're talking about the wrong kind of imbalance here.

Yes, the batteries will balance themself out under no load.

However, each individual battery wired as in the OP, will have a different level of use under load especially, thus, will not provide the full battery bank capacity. Given time, it will wear out individual batteries at different rates and lead to a significant amount of imbalance between the batteries in a battery bank and become less and less usable.

 

[sunshinestatestreaming]

It definitely won't work if you wire your batteries like that (from the ends of parallel batteries).

So if it won’t work this way, can you provide an example of how you would do it

 

[MisterSandals]

So if it won’t work this way, can you provide an example of how you would do it

Sure. There is a thread that is a nice body of work on this topic. Its quite long and detailed. But if you can get thru the first 4 posts, you will understand that current flows in the path of least resistance. And with batteries wired in various ways, in parallel in this case, the charge current does not reach each battery equally.

I think the best way is at the bottom of post #4. Its more doable with bus bars as you have them as opposed to a wiring scheme (where its hard to connect to midpoints).

Edit: Your exact case is covered in post #14 (which is similar to conclusion in post #4, example 9 but 1/3 offset, not midpoint).

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...

diysolarforum.com

 

[MisterSandals]

Those interconnects are so short that at the worst case there might arise a tiny inbalance in SOC between batteries, which will even out as you reach the steeper incline part of the charge or discharge curve.

Thank you for the opposing point of view. I am not sure if your are referring to the "interconnects" between the 3P batteries or between the 2 different 3P packs. I was referring to within the 3P packs. I posted a link to a thread that looks to be a definitive guide, but everything is up for debate and scrutiny.
Are you saying that the current flow calculations are incorrect? Or are you saying that current flow differences do not affect SOC?

This superstitious belief that any inbalance in SOC of parallel batteries is somehow dangerous seems only to be held by those who’ve never actually done it.

"Dangerous" is your word, not mine. I've wired cells incorrectly and have seen first hand how improper wiring can create imbalances. We see it nearly every day on this forum. Batteries and cells that become increasingly out of balance over time create a wide variety of problems, mostly manifested as significantly reduced battery capacity due to undercharging batteries/cells that get less charge current.

I'm all for learning something!

 

[Sverige]

Sure. There is a thread that is a nice body of work on this topic. Its quite long and detailed. But if you can get thru the first 4 posts, you will understand that current flows in the path of least resistance. And with batteries wired in various ways, in parallel in this case, the charge current does not reach each battery equally.

I think the best way is at the bottom of post #4. Its more doable with bus bars as you have them as opposed to a wiring scheme (where its hard to connect to midpoints).

Edit: Your exact case is covered in post #14 (which is similar to conclusion in post #4, example 9 but 1/3 offset, not midpoint).

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...

diysolarforum.com

Oh good! A whole thread of wrong people I’ll be happy to add something to the end of it to upset them all, but it will have to await me having more time to write.

I’ll give you a sneak preview though - calculations of theoretical current splits based on IR are worthless in real world situations because they ignore the feedback mechanism which occurs when cells actually receive inbalanced currents, which is that their terminal voltages rise proportionally in response to that current. This provides a self limiting mechanism whereby even even if one cell or a few cells in a string begin to receive more charge, eventually this evens out as their voltage rises relative to the others (due to receiving charge faster) and at that point they receive less and the relatively undercharged ones will then charge faster.

The very most you can say of such an arrangement is that it’s very marginally inefficient, not that it “definitely won’t work”!

 

[StuartV]

In short, your positive cable should be at the back of the pack, keep the negative at the front. The way you have them at the moment, it will use all the power from the front battery, causing the back two to charge the front battery. Also, the back batteries wont get fully charged, as the front one will use up the charge.

(laymens answer).

 

[rodrick]

Oh good! A whole thread of wrong people I’ll be happy to add something to the end of it to upset them all, but it will have to await me having more time to write.

I’ll give you a sneak preview though - calculations of theoretical current splits based on IR are worthless in real world situations because they ignore the feedback mechanism which occurs when cells actually receive inbalanced currents, which is that their terminal voltages rise proportionally in response to that current. This provides a self limiting mechanism whereby even even if one cell or a few cells in a string begin to receive more charge, eventually this evens out as their voltage rises relative to the others (due to receiving charge faster) and at that point they receive less and the relatively undercharged ones will then charge faster.

The very most you can say of such an arrangement is that it’s very marginally inefficient, not that it “definitely won’t work”!

In your sneak peek you just made our point as some will charge faster but the others will eventually catch up,well in the real world using Lifepo batteries that are over sized for our systems we may not hit full charge due to low solar inputs on some days which is fine for Lifepo batteries not so good for fla and as everyone knows it take time for batteries hooked in parallel to balance out evenly so you can end up with a large state of charge spread so if you only used your batteries like once a week you would be fine but in the real world we use them daily

 

[Mousie]

I have the 4 Renogy Smart batts and wired using the halfway method. Really wanted 5 but whilst I understand balancing parrallel banks, I think the OP may be referring to the BMS interconnects as their Renogy battery monitor can manage more than 4 interconnects but the Renogy manual say max 4 or else issues. So with six, I don’t know if anyone knows how the BMS interconnects behave with more than four. I think the app can handle more than four batts so asking the OP on that part. Or are you using 2 separate interconnect banks here? Dis you try 6 x 1 bank and how did the app handle this?

 

[Texas-Mark]

However, each individual battery wired as in the OP, will have a different level of use under load especially, thus, will not provide the full battery bank capacity. Given time, it will wear out individual batteries at different rates and lead to a significant amount of imbalance between the batteries in a battery bank and become less and less usable.

Size your cables and bus bars properly and it will be a non-issue. Especially for such short runs as shown here. The OPer’s setup looks fine.

 

[50ShadesOfDirt]

A consideration is the vendor (Renogy) saying not to do it ... we can always go self-supporting and do whatever we want, but this will most likely be a "void your warranty" scenario. OP would have to analyze whether or not this is a "void the warranty" w/ respect to Renogy, and a concern.

There might now be a record of you calling in and asking "can I hook up MORE than the allowed amount of these" ...

Don't get me wrong ... I love voiding the warranty in many test scenarios ... half a dozen cheap LFP's and a test bench (separate from the house) ... higher chance of explosion ... that's good stuff!

(if done safely, of course)

 

[HRTKD]

I have the 4 Renogy Smart batts and wired using the halfway method. Really wanted 5 but whilst I understand balancing parrallel banks, I think the OP may be referring to the BMS interconnects as their Renogy battery monitor can manage more than 4 interconnects but the Renogy manual say max 4 or else issues. So with six, I don’t know if anyone knows how the BMS interconnects behave with more than four. I think the app can handle more than four batts so asking the OP on that part. Or are you using 2 separate interconnect banks here? Dis you try 6 x 1 bank and how did the app handle this?

What are these BMS interconnects? Are you referring to the cables attached to the terminals or a communication connection? The Renogy batteries have no inter-battery communication. One battery has no idea that it is connected to another battery.

Even numbers of batteries are easier to connect than odd numbers of batteries. The connection method that @Daxo provided in post #4 looks good.

I suspect that the "no more than 4" restriction is because people tend to connect the newer technology batteries using old technology methods and end up with less than optimal results.

 

[Mousie]

Renogy Smart 100 ah Batts variety use communication interconnects and you can see them connected in two banks going to their Bluetooth Dongles on the wall in original post. Apparently they undertake auto balance functions on charging so they do see and talk to each other in the string.

 

[HRTKD]

Renogy Smart 100 ah Batts variety use communication interconnects and you can see them connected in two banks going to their Bluetooth Dongles on the wall in original post. Apparently they undertake auto balance functions on charging so they do see and talk to each other in the string.

Thanks for the correction. I didn't zoom into the picture far enough. I see the communication cables now.