ADVICE NEEDED ON BMS PRUCHASE!

[Embracing The Journey]

Purchased 8 180ah CALB 3.270-3.273 batteries. Connecting batteries in 4 groups of 2 (series) then connecting those groups in parallel for a 12v battery for our RV.

Will a S4 100ah BMS be a correct match with my battery pack described above or is another S? BMS be better?

 

[Pierre]

Consider 4s2p and 2 x 4s BMS’s , one across each series string ? If the one string dies you still have the backup of the other string.

 

[Steve_S]

You can use a 4S BMS to build one Battery Pack with paired cells, this would give you 12V/360AH but it is One battery and you are only watching (managing) 4 of 8 cells in the battery pack. if something goes awry then the pack shuts down.

You can build two 12V/180AH Battery Packs each with a 4S BMS and be able to manage each cell within that pack. If one pack fails for some reason the other keeps going.

There is technically nothing wrong with placing cells in parallel, especially if you know you have High Quality Premium Cells but if you have just one dubious cell paired to a good cell, the good cell could effectively camouflage a failure while it is happening. Often "Shlock Dealers" with put a mix of good & so-so cels and paired them accordingly to hide the weak cells and the BMS only monitoring 1/2 way would not know till it's too late.

The cost of a 100A 4S BMS is not very much. Typically if they are rated to 100A discharge, they "should" handle 50A charge rate. It is generally recommended to use a FET Based BMS rated at 25% higher than what you will actually pull so as to prevent from using the BMS to it's "limit". Therefore a 125-150A BMS provides lots of elbow room and safety margin.

The various BMS available can come with a wide assortment of features & functions, which one you will specifically need largely depends on what you want to do with the BMS and what you want the BMS to do for you. There are simple BMS that you plug in and just accept they are working. Then you can get ones which have Active or Passive balacing, some with BlueTooth interfaces which are programmable & can be actively monitored, some can communicate wit external devices like an Inverter or Charger and more. Of course features, functions and capabilities come with costs too.

Hope it helps, Good Luck.
Steve

 

[Giela]

Purchased 8 180ah CALB 3.270-3.273 batteries. Connecting batteries in 4 groups of 2 (series) then connecting those groups in parallel for a 12v battery for our RV.

Will a S4 100ah BMS be a correct match with my battery pack described above or is another S? BMS be better?

I will use the same setup but can't find myself a good BMS. I really want to see what's going on so a normal Daly isn't on option. Also the BMS Will adviced with bluetooth is not working for me. I bought on but it isn't working properly. The Chargery is the best option then?

 

[Steve_S]

A Chargery BMS8T will handle 2S to 8S cell configuration but 2S-4S requires an external power source of 15V @ 3A max.
Chargery only has the Display Module which you can interact with, it has no Bluetooth capabilities. The RS232 Interface only outputs data for monitoring purposes (no application for that is available from Chargery).

There are a few different BMS' that people use here that have Bluetooth and other features with great success. I cannot personally speak to them as I do not use them myself, I use Chargery because it fits my use case & my techy requirements. I have lost track of the "current" recommended/suggested ones. Things are developing quickly so it's a tough target to nail down which is better "today" versus what was 6 months ago even.

@Will Prowse Suggestion / Thought.
Would it be possible for you to updated Listing on the Website (linked to from the forum) for recommended BMS's with the features/functions and capabilities including the links to the BlueTooth apps etc for them. This would be a great of value for the folks here looking at the various options.

Have a look at TinyBMS, link below. This is a European SmartBMS with all the goodies & bells & Whistles and modular so you can add what you want/need for your application. Top Notch product with good reputation but now we are getting into more $ but it is good for comparing smarter BMS' against each other.

https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4

 

[Giela]

A Chargery BMS8T will handle 2S to 8S cell configuration but 2S-4S requires an external power source of 15V @ 3A max.
Chargery only has the Display Module which you can interact with, it has no Bluetooth capabilities. The RS232 Interface only outputs data for monitoring purposes (no application for that is available from Chargery).

There are a few different BMS' that people use here that have Bluetooth and other features with great success. I cannot personally speak to them as I do not use them myself, I use Chargery because it fits my use case & my techy requirements. I have lost track of the "current" recommended/suggested ones. Things are developing quickly so it's a tough target to nail down which is better "today" versus what was 6 months ago even.

@Will Prowse Suggestion / Thought.
Would it be possible for you to updated Listing on the Website (linked to from the forum) for recommended BMS's with the features/functions and capabilities including the links to the BlueTooth apps etc for them. This would be a great of value for the folks here looking at the various options.

Have a look at TinyBMS, link below. This is a European SmartBMS with all the goodies & bells & Whistles and modular so you can add what you want/need for your application. Top Notch product with good reputation but now we are getting into more $ but it is good for comparing smarter BMS' against each other.

https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4

That's a great idea Steve. Maybe the Chargery is also something that will work for me. I don't really understand what you mean by you need an external powersupply of 15V @ 3ah max.

Like I said, have a 8S 12V pack (4x2S). Will the Chargery work?

 

[John Frum]

[QUOTE="Giela, post: 99021, member: 8099"
Like I said, have a 8S 12V pack (4x2S). Will the Chargery work?
[/QUOTE]
What is (4x2S)?

 

[Giela]

I have 4 packs of two cells. So four packs of two in parallel and then in serie so I get 12V but double the AH.

Like this:

 

[John Frum]

I have 4 packs of two cells. So four packs of two in parallel and then in serie so I get 12V but double the AH.

Like this:

Cool, Thats means a 4s bms each lead balancing 2 cells.

 

[Giela]

Yes, but I was thinking about an 8S BMS so I can monitor each single cell

 

[John Frum]

Yes, but I was thinking about an 8S BMS so I can monitor each single cell

8s is for a 24 volt battery.

 

[Steve_S]

The BMS can be powered by the pack itself IF the pack has the voltage. a 12V pack (4 LFP cells) isn't enough. Now that being said, the requirement is for 15 Volts capable of delivering 3A for their two standard electro-mechanical Contactors. If using Contactors which require less volts/amps like the TE/Kilovac EVE series that external voltage requirement can drop a bit. Depending on Configuration, the Chargery normally uses two relays and can be used in Common-Port or Separate-Port configurations. With Common-Port, it is possible to eliminate One Contactor by using an Optocoupler to receive the two relay signals and actuate only one contactor.

For more detailed info, refer to this post below. There is my DRAFT Chargery BMS8T Owner's Manual attached to that post. It may be worth your while to download that and review it, it should answer several of your questions. The Official Manuals should be out next week, there is lag between Json in China and myself and he's been "tweaking" a few things too.

Trying to find a BMS to fit my setup

Welcome to the forum. Regarding setup. I have to say, the 280AH cells ate 5.2Kg EACH / 11 Lbs ! These buggers are HEAVY and put 16 together, you will need help shifting it all around. 48VDC pack requires 16 LFP cells 88Kg / 194 Lbs. I highly recommend applying KISS rules to your build...

diysolarforum.com

You can ONLY MONITOR CELLS Which have a Balance Lead Attached to it. If Cells are paralleled you will only see the median of BOTH cells. This is what I mean by "ghosting cells".

Typical 4S + 4S w single BMS8T
this will allow you to monitor all cells, as there is one lead per cell.


Here we have 4 Cells in Parallel but 2 cells in parallel is similar.
This will only monitor cells with the leads attached. This shows an "average" of the paralleled cells.
In this instance below, you are reading the average of the 4 cells in parallel per lead.


! NOTE !
The BMS Harness is only 600mm long. If extending the wires, they should be of equal length and have soldered & heat-shrink wrapped connections, including the terminal rings on the ends. Such an installation is usually within one single cabinet with all cells close at hand to the harness.

 

[Giela]

The BMS can be powered by the pack itself IF the pack has the voltage. a 12V pack (4 LFP cells) isn't enough. Now that being said, the requirement is for 15 Volts capable of delivering 3A for their two standard electro-mechanical Contactors. If using Contactors which require less volts/amps like the TE/Kilovac EVE series that external voltage requirement can drop a bit. Depending on Configuration, the Chargery normally uses two relays and can be used in Common-Port or Separate-Port configurations. With Common-Port, it is possible to eliminate One Contactor by using an Optocoupler to receive the two relay signals and actuate only one contactor.

For more detailed info, refer to this post below. There is my DRAFT Chargery BMS8T Owner's Manual attached to that post. It may be worth your while to download that and review it, it should answer several of your questions. The Official Manuals should be out next week, there is lag between Json in China and myself and he's been "tweaking" a few things too.

Trying to find a BMS to fit my setup

Welcome to the forum. Regarding setup. I have to say, the 280AH cells ate 5.2Kg EACH / 11 Lbs ! These buggers are HEAVY and put 16 together, you will need help shifting it all around. 48VDC pack requires 16 LFP cells 88Kg / 194 Lbs. I highly recommend applying KISS rules to your build...

diysolarforum.com

You can ONLY MONITOR CELLS Which have a Balance Lead Attached to it. If Cells are paralleled you will only see the median of BOTH cells. This is what I mean by "ghosting cells".

Typical 4S + 4S w single BMS8T
this will allow you to monitor all cells, as there is one lead per cell.
View attachment 16802

Here we have 4 Cells in Parallel but 2 cells in parallel is similar.
This will only monitor cells with the leads attached. This shows an "average" of the paralleled cells.
In this instance below, you are reading the average of the 4 cells in parallel per lead.
View attachment 16803

! NOTE !
The BMS Harness is only 600mm long. If extending the wires, they should be of equal length and have soldered & heat-shrink wrapped connections, including the terminal rings on the ends. Such an installation is usually within one single cabinet with all cells close at hand to the harness.

Hi Steve, thanks for you reaction. If you have 2 (or more) cells in parallel. Won't they balance eachother?

 

[Steve_S]

Hi Steve, thanks for you reaction. If you have 2 (or more) cells in parallel. Won't they balance eachother?

Well, yes & no. They, in theory, should balance between themselves while AT RES. During a Charge Cycle, they are essentially stupid and the cells will take as much volts & amps as they can but if one cell has a slightly lower resistance it will fill up faster than one with a higher resistance. Now you get some cells higher and others that are lower because the threshold max is 3.65V per cell. Take one cell @ 3.65V and the paired pal at 3.30V the BMS would see that "pair" as 3.475V and keep pushing to it. By the time the 3.30V cell hits 3.65V the other one could be at 4.0 (near death) and so you have an issue that will compound itself. Now if the BMS cuts off the pair @ 3.65V (the max Volts for LFP and 100% full) the BMS has no way to differentiate the pairs so you could have one Hi cell (even over volts) and one Lo cell and it would not know it.

All that said, it is never good to take LFP to 100% as your tickling the dragon's toes there. It is commonly suggested to operate between 80-90% of capacity to ensure longevity & maximum cycles possible. This also offers passive protection against Overcharging the cells.
3.285V per cell is 90% full, X 16 cells = 52.56V. The Bottom @ 2.75V per cell is 10% from the bottom of 2.5V per cell, which is 44V for cutoff.

There is more to it but I am just trying to keep it simple and prevent a headache for anyone reading it... I'm just keeping the numbers simple for that purpose.

A final note of sorts. With EV's using Li-Ion NMC cells they are usually configured in parallel and then set in series. EV's use between 350VDC to 450VDC depending on brand/model. Each individual cell is fused independently as well as some other safeties depending on the type of pack assembly. The BMS' to manage an EV Battery Bank is very complex and seriously expensive. While this is the current Norm for an EV they do manage their battery packs quite a bit differently, especially with the fast charge High C-Rate they can accept. Folks often do not realize the big differences and assume all "Lithium" is the same which it is definitely not.

woof, too much time on the board today....

I hope I covered your Q's. Others can fill in blanks in need be.
Steve

 

[Giela]

Well, yes & no. They, in theory, should balance between themselves while AT RES. During a Charge Cycle, they are essentially stupid and the cells will take as much volts & amps as they can but if one cell has a slightly lower resistance it will fill up faster than one with a higher resistance. Now you get some cells higher and others that are lower because the threshold max is 3.65V per cell. Take one cell @ 3.65V and the paired pal at 3.30V the BMS would see that "pair" as 3.475V and keep pushing to it. By the time the 3.30V cell hits 3.65V the other one could be at 4.0 (near death) and so you have an issue that will compound itself. Now if the BMS cuts off the pair @ 3.65V (the max Volts for LFP and 100% full) the BMS has no way to differentiate the pairs so you could have one Hi cell (even over volts) and one Lo cell and it would not know it.

All that said, it is never good to take LFP to 100% as your tickling the dragon's toes there. It is commonly suggested to operate between 80-90% of capacity to ensure longevity & maximum cycles possible. This also offers passive protection against Overcharging the cells.
3.285V per cell is 90% full, X 16 cells = 52.56V. The Bottom @ 2.75V per cell is 10% from the bottom of 2.5V per cell, which is 44V for cutoff.

There is more to it but I am just trying to keep it simple and prevent a headache for anyone reading it... I'm just keeping the numbers simple for that purpose.

A final note of sorts. With EV's using Li-Ion NMC cells they are usually configured in parallel and then set in series. EV's use between 350VDC to 450VDC depending on brand/model. Each individual cell is fused independently as well as some other safeties depending on the type of pack assembly. The BMS' to manage an EV Battery Bank is very complex and seriously expensive. While this is the current Norm for an EV they do manage their battery packs quite a bit differently, especially with the fast charge High C-Rate they can accept. Folks often do not realize the big differences and assume all "Lithium" is the same which it is definitely not.

woof, too much time on the board today....

I hope I covered your Q's. Others can fill in blanks in need be.
Steve

Thanks, that is some good and understandable information

But do you not have the same with a simple 4S 12V pack for example? If one cell fill up faster then the other, then you have that problem anytime right?

But for example, with this BMS:

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I can monitor and balance every cell of my 8S (4 packs of 2 cells) 12V pack right?

 

[Ampster]

I can monitor and balance every cell of my 8S (4 packs of 2 cells) 12V pack right?

There will be no voltage difference between the two cells because they will rest at the same voltage. It might even confuse the BMS because it expects to see 3.2 voltage increments from lead to lead.

 

[Embracing The Journey]

Hello, thanks for info and KIS. Providing additional information to assist in pointing me in the right direction on a BMS.

1. we are completly off grid, no grid access at all nor will there be.

2. not electricity savey, working at learning. want to learn/know, but most of all want to be safe and not ruin the 5thw rv or batteries.

3. want/need/love bluetooth monitoring as a means to monitor/learn and understand proper/correct settings.

4. like bells and whistles on BSM to protect us from my ignorance and willing to pay more $ for that.

Like the Tiny BMS suggestion, will look at it. reviewing the Electrodacus BMS as well.

(any advice, pros/cons on either?)

thank you!

 

[Ampster]

......any advice, pros/cons on either?

I am not familiar with either one but data is important to me. When running a Frankenpack of used cells, it was invaluable to me to observe the changes in cell deltas at various stages of charging and discharging. With my new pack that analytical ability will allow me to isolate a weak cell and replace it with a spare.

 

[Craig]

Hello, thanks for info and KIS. Providing additional information to assist in pointing me in the right direction on a BMS.

1. we are completly off grid, no grid access at all nor will there be.

2. not electricity savey, working at learning. want to learn/know, but most of all want to be safe and not ruin the 5thw rv or batteries.

3. want/need/love bluetooth monitoring as a means to monitor/learn and understand proper/correct settings.

4. like bells and whistles on BSM to protect us from my ignorance and willing to pay more $ for that.

Like the Tiny BMS suggestion, will look at it. reviewing the Electrodacus BMS as well.

(any advice, pros/cons on either?)

thank you!

If you are 12v. I think hands down the electrodacus would be the way to go. And I am a Chargery guy. I do not use electrodacus because it wouldn't work for me. But if it did I would.

 

[madmax]

I may have undersized my bms. While the discharge is fine, 50a charge rate is a big limiter, considering 4000w of solar input.

A single bms on a 2p7s was good in theory but the charge rate is limiting...