Struggling to put my BMS strategy together

[BillCaswell]

Hello All,
- I am swimming in the amount of information available on this forum that I've been reading for the past few weeks.
- I have some gaps in my thinking that I need to close.
- I am planning a 96 cell installation in my sailboat organized into 4 battery packs of 24 Fortune 100ah cells 2C (6C peak, 10 sec) arranged as 3P8S to provide 24 volts to the house system. (see the enclosed picture)
- I do not want to cut corners. This build needs to be bullet proof using the most reliable and safest components I can source.
- The rest of electrical system is Victron Energy.

96 cells divided into 24 cells in a 3P8S configuration to provide 24 volts
4 x battery packs to create the house bank
3P gives me 600 amps continuous at 24v
The house bank is also used the drive 20 hp (14 kW) electro-hydraulic bow thruster motor. It draws 700 amps. It is used sporadically 3-10 seconds at a time. The specs on the Fortune cells appear to be the best fit.
I believe that this requires that I use a contractor

I am overwhelmed by the discussions regarding the best BMS to focus my attention on. REC, Batrium, Chargery and Electrodacus, and Orion, etc.

Questions:

- Does my application of the 3P8S packs x 4 house bank configuration make is it obvious to others which BMS to look at as a first, second and third choice?
- Will I be attaching a BMS lead to each cell or one lead per each 3P group?
- Do I need a master-slave BMS to manage all four packs that make up the house bank, or do I treat each battery pack as independently managed by their own BMS without any communications between each battery?

Thanks in advance for any insights you can provide!

 

[BillCaswell]

I've looked at the REC website and can't figure out which of their products to specify. I had an initial reach out from Current-Connected but after asking me for some clarifications they have gone dark on me.

 

[Steve_S]

These are 24V/8S so you will require an 8S BMS for each pack.
Each parallel set of cells is viewed by a BMS as ONE unit. The BMS Sense/Balance wire will go Mid Busbar on the (+) side.
IF attempting to dump that many Amps and manage that, pushes you out of MOSFET BMS' into using Relays/Contactors that can handle high amperages (small Fets used for BMS' don't cut it). *BEWARE of High Amp FET Based BMS' !
None of those packs (singularly) will be able to handle 700A, at best you could squeeze 300A bursts IF the cells can actually do 3C Discharge. Now with 300AH Cells @ 1C, they can safely dump up to 300A without reaching over the edge.
There is NO NEED for a Master Slave setup. Each Battery Pack is it's own entity with it's own BMS & Relays/Contactors.

Clarity is important here....
A Battery Pack is a collection of cells & a BMS - ONE Battery Pack. (regardless if there are cells in parallel within the pack)
A Battery Bank is a collection of Complete Batteries in Parallel ! this can be 2 or 20 packs !
In your case, this is 4 Battery PACKS in One Bank of Batteries.
4, 300A Battery Packs for 1200A Available (they share/divide load & charge) in one bank will work.
Charging that bank will require serious input !

Appreciate the 100AH cells are just that and by doing 3P they are still 100AH cells and subject to those limits.
Burst Rates should NOT be a consideration for regular use, that capability is not for that purpose, it is for outlier cases.
You would be far better off buying 304AH Cells and keeping it simpler with a straight 8S config that allows for the pack to discharge up to 300A (1C rate).

PARALLEL CELL GOTCHA ! If you parallel cells they REALLY NEED TO BE MATCHED & BATCHED to be identical. Meaning that they have identical cell IR (Internal Resistance) throughout the entire Working Voltage Range. So if the cells are at 3.000, 3.200 or 3.400 Volts per cell that they have the same Internal Resistance or the set will unbalance as time progresses putting more strain on stronger cells to compensate... This causes issues! Remember that Lithium Based battery cells ARE Millivolt & Milliohm sensitive, it is NOT Brute Force tech like lead acid. BTW: Many people have issues with Paralleled cells within packs and not realizing why, end up chasing their tails because they bought unmatched cells.

Relays or Contactors:
Both have Pros & Cons... Both are designed for higher Amperage Handling, relays are electro-mechanical while Contactors are Solid State with heavy duty FETS and support circuitry for the purpose. Relays typically use more power to function and MUST be the type that will fail OPEN should they fail, this prevents power from flowing in such a case. Avoid Low Cost Relays ! Contactors use less power and can work quite well if properly setup and if they have active cooling as they do get pretty warm to hot under high loads. *NB* EV's use Relays NOT Contactors and for good reason.

Hope it helps, Good Luck.

 

[BillCaswell]

Hope it helps, Good Luck.

This is a lot of information. I will be reading this several times to fully digest. I believe that others in my situation will find this info useful as well. Thanks for taking the time!

I would like to come back with some clarifying questions, one or two at a time. Just let me know when I've exhausted your patience!

 

[Steve_S]

This is a lot of information. I will be reading this several times to fully digest. I believe that others in my situation will find this info useful as well. Thanks for taking the time!

I would like to come back with some clarifying questions, one or two at a time. Just let me know when I've exhausted your patience!

I do not normal "watch" threads I reply to anymore but am now watching this thread... Watching everything became somewhat overwhelming after a few years on here. I now only selectively respond and rarely watch the occasional thread. I've written a few docs, manuals & guides on this subject, even BMS Manuals & Docs for companies... You might say I have left an "Extended Trail" (like deer tracks in fresh snow) lol.

 

[BillCaswell]

Relays or Contactors:
Both have Pros & Cons... Both are designed for higher Amperage Handling, relays are electro-mechanical while Contactors are Solid State with heavy duty FETS and support circuitry for the purpose. Relays typically use more power to function and MUST be the type that will fail OPEN should they fail, this prevents power from flowing in such a case. Avoid Low Cost Relays ! Contactors use less power and can work quite well if properly setup and if they have active cooling as they do get pretty warm to hot under high loads. *NB* EV's use Relays NOT Contactors and for good reason.

I bought these from batteryhookup.com. As you can see, the little plastic nipple is bent over on the righthand side.

Question:
1. Is this damage or is it ok to use?
2. What is this nipple used for?

 

[Rocketman]

My guess on Contractor you don’t want to use the broke one in a boat. The salt air will corrode the inside guts over time - just when you need it…

Let me add my perspective- I use a Batrium BMS for my MotorHome. 540ah 12v battery. I like the bms. (I use that same contactor).

With a Batrium it Will Monitor every supercell (more than one cell hooked in parallel). But if there is a problem with one supercell (goes too high/low) it will shut down the whole pack.

Now I like those fortune cells (used eight 25ah ones to make a portable battery). They seem REALLY good! I think they are the right battery for a sailboat. They stay better in sync than my 272ah cells.

One thing you could do if using Batrium - is actually get two Batrium Core bms’s. Have two batteries on one and two batteries on another. If one died - you could reconfigure to have them all on one Core.

The downside of that is then you would not use the Batrium to Can-Buss into the Victron. You would need a BMV712 or Smartshunt for the Victron battery levels.

Good Luck!

 

[Steve_S]

The one on the right is Junk ! Do not use.
I actually have a box full of those TE-Kilovac's. Never wound up using them because the Chargery DCC's came out of our experiments & testing where Jason from Chargery took up the challenge and developed them... This was after I had commissioned 500A & 1000A Solid State contactors from a company in China.

I eventually retired my fleet of Chargery BMS' with all the extras and changed my fleet to JKBMS' making my life a heck of a lot simpler.

 

[BillCaswell]

Clarity is important here....
A Battery Pack is a collection of cells & a BMS - ONE Battery Pack. (regardless if there are cells in parallel within the pack)
A Battery Bank is a collection of Complete Batteries in Parallel ! this can be 2 or 20 packs !
In your case, this is 4 Battery PACKS in One Bank of Batteries.

Thanks, I corrected my original post.

 

[BillCaswell]

@Steve_S, you wrote, "Each parallel set of cells is viewed by a BMS as ONE unit. The BMS Sense/Balance wire will go Mid Busbar on the (+) side" which is consistent with other posts and documentation that indicates putting the balance wire at the mid-point of the bus bar for batteries in parallel. But I also see documentation that says to put the balance wire at the end of the bus bar. The picture is from the Rec-BMS documentation, page 19, fig. 7. Is the placement of the balance wire dependent on the BMS mfg., or is there a subtly that I am missing? And why one end vs. the other end?

 

[Rocketman]

I think being consistent is most important- I don’t know why Rec would specify the end cell. That may be a good question to ask them and then let us know.

 

[BillCaswell]

I think being consistent is most important- I don’t know why Rec would specify the end cell. That may be a good question to ask them and then let us know.

I've sent them an email asking for a response. Because I am new at this, I'm not sure what information is known to those with more experience and that which is truly a good question.

 

[Steve_S]

I think that virtually all BMS Makers will indicate to place @ Mid-Point of the (+) side on a busbar with paralleled cells. Now putting them all on one end (the most outlying) is fine as well AS LONG AS IT IS UNIFORM across the pack is okay too but it may present slightly differently when viewing configuring BMS parameters. I use Best Practices as established and this applies to EV-LFP Packs as well and how they do it too.

I suggest that you should likely download THIS PDF Resource which may answer several questions and provide other info... do check the links on the end to other resource source info as well. I wrote this up and gave it to one of our best vendors and my personal favorite.
Luyuan Tech Basic Lifepo4 Guide V1.0A

I will again reiterate that unless you are using properly Factory Matched & Batched cells it is "not" a wise idea to put cells in Parallel within a battery pack.

 

[BillCaswell]

I suggest that you should likely download THIS PDF Resource which may answer several questions and provide other info... do check the links on the end to other resource source info as well. I wrote this up and gave it to one of our best vendors and my personal favorite.
Luyuan Tech Basic Lifepo4 Guide V1.0A

Can I assume that "THIS PDF" refers to the link at the end of the paragraph and NOT an embedded link that is accessed by clicking on the "THIS PDF" phrase. (Sorry for being so literal)

 

[Steve_S]

There is no embedded link, it is the link at the bottom. That takes you to our resources and you can download the PDF File.

 

[BillCaswell]

There is no embedded link, it is the link at the bottom. That takes you to our resources and you can download the PDF File.

Thanks, just wanted to confirm. I appreciate your patience as I learn all that I can...