BMS Confusion for a 8S3P battery

It is time to pull the trigger and order 24 x EVE 280 from Amy to build the 840ah 8S3P battery
The question she has just asked is which BMS do I want and frankly, I have no idea.

Research on here suggests I don't want a Daly
Which leaves JBD and Chargery being offered
JBD seems most popular on this thread

As we do have some big loads onboard running multiple 240v fridge freezers, 240v water pump, 240v hot water system and a 240v still/boiler I'm guessing we need a bigger BMS but just how big?
The two items in bold are only run on sunny days and big solar support or with genset assist

Looking at the Victron battery monitor we have never seen more than a 60amp draw and that's only for a few minutes as I madly scramble to shut stuff down of fire up the generator.
Usual draw is no more than 20 amps as fridges kick in and a bit more for several minutes if having a shower as the pump is used


If I have a 100 amp on each 24v battery is that enough?
Does it equate to a 300 amp across the system?

One like this???

Thanks in advance

Hot Water tanks are one of the most wasteful energy pigs.
Think of it like having your car idling 24 hours a day, just because you might want to go for a 15-minute spin. On-Demand hot water works quite well and is more "frugal".

24V @ 250A = 6000W delivering which is a max of 50A @ 120V or 25A @ 240V (uncorrected for inverter efficiency).
A Low Frequency Inverter is capable of 3X surge while High Frequency only 2X surge capability.

Paralleling cells to make one pack should ONLY be done with Matched & Batched cells, NOT Bulk Cells.
Each battery pack needs a BMS and Fuse.
24V is 8S, regardless of the number of paralleled cells within the battery pack.
Remember these cells are 5kg/11lbs each 24V/280AH/8S with case and dressed to work 90 LBS.
Building 3 24V/ simple 8S battery packs will divide load/charge, will be more fault-tolerant and less stressful on the packs in general.

For proper fail-safe operation, each battery should be capable of fully operating as a "StandAlone" battery in the event the others cut off for any reason. Now of course that also depends upon your inverter and just how much it can pull from the batteries but you have to account for surge potential plus if you have kids, or worse teens about, expect "stuff" to happen.

I'm 24V with Samlex EVO 4024 4000/12000W Inverter. My 280AH packs are built to handle 250A out (except my two 175 packs) using 300A labeled equipment. MIdnite solar Classic-200 with 250A E-Panel that handles it. Wired with 4/0 because my wire run from Inverter to Batt-pack is just under 14' collective. I use the Chargery BMS' as those suit my purpose. Each pack also has a QNBBM-8S Active Balancer (kinda $$) but there are Heltec Active Balancers, Hankzor Active Equalizer ones as well.

My suggestion for a BMS is not to get hung up on 100A (most are because that's what drop ins are and it's subliminal) I suggest built to the Battery Handling Capacity or up to 250A max. Even if you never use 250A "now", tomorrow happens and we can't tell what it will be. Best to Build it Right the first time and not have to revisit for an upgrade. If you had 150AH cells then obviously the max would be 150A.
I suggest a BMS capable of 200-250A derate it a bit for margin.
Contactor Relay type of BMS can do this as the relays handle the power.
New FET Based BMS rated for 200A & 250A have also come available (not that common yet) so check on the forum... ignore Daly.

hope it helps

Steve_S said:

Hot Water tanks are one of the most wasteful energy pigs.
Think of it like having your car idling 24 hours a day, just because you might want to go for a 15-minute spin. On-Demand hot water works quite well and is more "frugal".

​

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Totally agree but it's what's onboard.
It only ever gets charged when batts at at 97% and the 2500 watts of solar are smashing amps in - or now, with a failing AGM bank, it gets done with the 7.5 kVA Genset as I give the batteries a head start charge in the morning.

Steve_S said:

24V @ 250A = 6000W delivering which is a max of 50A @ 120V or 25A @ 240V (uncorrected for inverter efficiency).
A Low Frequency Inverter is capable of 3X surge while High Frequency only 2X surge capability.

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We have a Victron 5000/120 24v

Steve_S said:

Paralleling cells to make one pack should ONLY be done with Matched & Batched cells, NOT Bulk Cells.
Each battery pack needs a BMS and Fuse.

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Asking Amy if that is done - there is test data on each battery but......

Steve_S said:

24V is 8S, regardless of the number of paralleled cells within the battery pack.
Remember these cells are 5kg/11lbs each 24V/280AH/8S with case and dressed to work 90 LBS.

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Weight is ok, currently we have 8 X 220ah AGM, these LFP will be considerably lighter

Steve_S said:

Building 3 24V/ simple 8S battery packs will divide load/charge, will be more fault-tolerant and less stressful on the packs in general.

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Was what we were thinking
Am sure we could get away with 2 but thought the extra capacity and light work would be a better thing.

Steve_S said:

For proper fail-safe operation, each battery should be capable of fully operating as a "StandAlone" battery in the event the others cut off for any reason. Now of course that also depends upon your inverter and just how much it can pull from the batteries but you have to account for surge potential plus if you have kids, or worse teens about, expect "stuff" to happen.

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No kids - We do have a ships cat and we are very careful to load share
But yes, we did want it so if one dropped out we were still running on 2 and, at a pinch one in an emergency if shutting some refrigeration down
After reading the whole post I now see the need for the larger amperage BMS

Steve_S said:

I'm 24V with Samlex EVO 4024 4000/12000W Inverter. My 280AH packs are built to handle 250A out (except my two 175 packs) using 300A labeled equipment. MIdnite solar Classic-200 with 250A E-Panel that handles it. Wired with 4/0 because my wire run from Inverter to Batt-pack is just under 14' collective. I use the Chargery BMS' as those suit my purpose. Each pack also has a QNBBM-8S Active Balancer (kinda $$) but there are Heltec Active Balancers, Hankzor Active Equalizer ones as well.

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We run our 250w panels 3x3 through a midnite classic 150
I did consider the chargery bms and it is on offer but I was under the impression that they were more "involved" so , being a newb ruled them out.

Steve_S said:

My suggestion for a BMS is not to get hung up on 100A (most are because that's what drop ins are and it's subliminal) I suggest built to the Battery Handling Capacity or up to 250A max. Even if you never use 250A "now", tomorrow happens and we can't tell what it will be. Best to Build it Right the first time and not have to revisit for an upgrade. If you had 150AH cells then obviously the max would be 150A.
I suggest a BMS capable of 200-250A derate it a bit for margin.
Contactor Relay type of BMS can do this as the relays handle the power.
New FET Based BMS rated for 200A & 250A have also come available (not that common yet) so check on the forum... ignore Daly.

hope it helps

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And thanks for all that but here be the issue, apart from Daly I have not yet found the elusive 200-250amp BMS suitable for 24v batts

Is this heltec a likely candidate as a 250amp BMS?
Discharge of 2.1is low but a saw mention made in other posts of somehow being able to change that?

I'm in the same situation. I originally looked at building 3 x 8S1P banks and hooking them up in parallel and sharing the load over 3 BMS's but everyone on here said not to.
Are you building a 8S3P battery or 3 x 8s1p battery banks? Decided on a BMS yet?

I'm in Australia and found this locally made product. There is an upgraded version using 2 x 240 latching relays. Slightly less than what i wanted but still adequate at the moment.
https://www.ev-power.com.au/product/bcu-nev/

JimmyL said:

I originally looked at building 3 x 8S1P banks and hooking them up in parallel and sharing the load over 3 BMS's but everyone on here said not to.

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I very Highly doubt anyone told you that 3 packs in Parallel is bad. QUITE THE OPPOSITE. Each pack can run independently if others cut off. They share both the Load Demanded & the Charge push (destress on batteries).

Putting cells in Parallel inside one Battery Pack is NOT advisable and most certainly NOT with Bulk Cells... Should only ever be done with properly Matched, Batched & Binned cells.

Steve_S said:

I very Highly doubt anyone told you that 3 packs in Parallel is bad. QUITE THE OPPOSITE. Each pack can run independently if others cut off. They share both the Load Demanded & the Charge push (destress on batteries).

Putting cells in Parallel inside one Battery Pack is NOT advisable and most certainly NOT with Bulk Cells... Should only ever be done with properly Matched, Batched & Binned cells.

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I think I ask the question on the Electrodacus forum and everyone said its too complex and one 8S3P is better. I much prefer individual packs so the whole system doesn't shut down.

I'm only buying cells from Amy. Unfortunately have been sent 8x LF280N and 8x LF280K. Not sure if they should be paralleled together in one pack.

Make 2 8S packs, one N & one K, K's are slightly larger too. I have NOTHING NICE (in 5 languages) to say about Dacus Comment.

And what BMS? I have found an Australian BMS that uses 2 x 240 amp latching relays on charge and load. Great for 1 unit but probably too expensive to 2 systems.

JimmyL said:

Are you building a 8S3P battery or 3 x 8s1p battery banks?

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8S3P is 3x 8S batteries in parallel... so its the same as 3x 8S1P. (where the 1P is redundant or implied in 8S)

Are you sure you're not thinking about 3P8S where you put 3 cells in parallel, and 8 of those in series?

Steve_S said:

I very Highly doubt anyone told you that 3 packs in Parallel is bad.

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Agreed. I think JimmyL might be confusing 3P8S which has been a controversial topic (how many cells to parallel before putting into series).

I think a lot of this discussion revolves around this misuse of 8S3P (which is supposed to be 3x 24v packs connected in parallel, and each requiring an 8S BMS).

Gosh i hope i didn't muddle the terms...

MisterSandals said:

8S3P is 3x 8S batteries in parallel... so its the same as 3x 8S1P. (where the 1P is redundant or implied in 8S)

Are you sure you're not thinking about 3P8S where you put 3 cells in parallel, and 8 of those in series?


Agreed. I think JimmyL might be confusing 3P8S which has been a controversial topic (how many cells to parallel before putting into series).

I think a lot of this discussion revolves around this misuse of 8S3P (which is supposed to be 3x 24v packs connected in parallel, and each requiring an 8S BMS).

Gosh i hope i didn't muddle the terms...

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Yeah i'm probably confusing everyone and myself.

Originally i wanted 3 or 4 separate 8S packs (individual BMS) similar to commercially available batteries in racks that can just be paralleled. Quite a few said it wasn't a good idea (too complex) and instead build 1 pack 3or4P8S.

JimmyL said:

Quite a few said it wasn't a good idea (too complex) and instead build 1 pack 3or4P8S.

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I have a 2P4S pack that works fabulously. I tested and matched 8 cells out of 13 that I had available.

The problem with a 2P4S pack is that the BMS supplies one wire to each pair of cells and there is no individual cell monitoring. If you have a 3P8S pack, then you have 3 cells in parallel (8 times) with only a single BMS wire to monitor 3 cells at a time. So if one or even two of the cells in a parallel "bunch?" go bad, it might not be detected or noticed by the BMS. The good news though is that its a buddy system where a strong cell can help a weaker cell.
With this thought, i took my 8 most similar cells and paired strongest with the weakest. Then second strongest with second weakest... this gave me as good as i could achieve with equal pairs.

If you have 3P, then it would take a huge effort to get this right. And even then, in the event of a single cell failure, there are 2 other cells joined to it in parallel to carry the load.

And a 3P8S battery would only require one 8S BMS.
A 8S3P battery bank would require 3 BMSs (one for each 8S battery).

I opted for a single BMS. Others choose individual cell monitoring and a BMS per battery.

JimmyL said:

.
Are you building a 8S3P battery or 3 x 8s1p battery banks? Decided on a BMS yet?

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I am in Aus as well and went this BMS

Using matched and batched cells from Amy
8 cells into 24v X 3
Each with its own 200amp BMS
3 for redundancy and less stress on the batts.
Boat can run on 2 and probably run on one bank of 8 cells for 24v @ 280ah at a pinch

MisterSandals said:

If you have 3P, then it would take a huge effort to get this right. And even then, in the event of a single cell failure, there are 2 other cells joined to it in parallel to carry the load.

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There is unfortunately a gotcha in that.
3 cells in parallel A-B-C. Cell B 'fails'. A&C try to make up for it but it drags the set down, the lowest common denominator effect. The result is that it drags the entire pack down by a percentage.

Worst Case, is B cell failure is a catastrophic one, leakage/bloat thermal ....
With individual cells being monitored its likely to catch the severe fault for the single cell, and disable the pack for protection (attention) which can be masked by paralleled cells.

Think of "runner" cells, they are the ones most likely to create issues, including Thermal. Think about Li-Ion in EV's paralleled cells & thermal failures.

Honestly the cost of a BMS = 1 or 2 cells cost and what it does and how it protects the investment, to me makes sense to do.
But then, I'm rural & remote offgrid, can be snowed in for days in winter and depend on my gear to live, so I'm a bit particular about it, I guess.

Steve_S said:

.
But then, I'm rural & remote offgrid, can be snowed in for days in winter and depend on my gear to live, so I'm a bit particular about it, I guess.

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And we are several months at a time away from civilisation as well so have the same considerations.

Steve_S said:

Honestly the cost of a BMS = 1 or 2 cells cost and what it does and how it protects the investment, to me makes sense to do.
But then, I'm rural & remote offgrid, can be snowed in for days in winter and depend on my gear to live, so I'm a bit particular about it, I guess.

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My place is also rural and i work away so the pack has to be reliable for the family. What reliable BMS? FET or contactor?

Simi 60 said:

And we are several months at a time away from civilisation as well so have the same considerations.

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Are you happy with the chinese BMS?

JimmyL said:

Are you happy with the chinese BMS?

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Only finalised payment today.
I don't care who makes it as long as it works.
JBD/Overkill seems to get good reviews here.

Simi 60 said:

Only finalised payment today.
I don't care who makes it as long as it works.
JBD/Overkill seems to get good reviews here.

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I don't care either but there is a difference between running a battery for camping and then running your home 24/7

JimmyL said:

I don't care either but there is a difference between running a battery for camping and then running your home 24/7

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Yep, but plenty on here running JBD for more than camping
They get better rating and seem more reliable than Daly and that's what many commercial "drop in" batteries use like this for example

I myself am the "Chargery Guy" as such, BMS8T-300's with DCC's, see the top link in my signature.
I also have a "Hot-Swap" board for the DCC's if one fails, the Board is setup with dual TE-Kilovac 200A Energy Saver Relays, Delay Board & Shunt.
But I also have a JBD120A/4s and am building another 24V/105AH pack using a JBD-150A/8S for my toolshed. These are very light duty.

My personal take with 280AH packs, use a BMS that is capable of handling the cells attached, because our usage & needs change, it is simply a fact of life. Build it for "today" and tomorrow you'll need more for one reason or another. I build my system to handle 300A knowing I'll only hit 250A and maybe a surge over that IF needed. My typical running Amp draw is between 6-12A. 24V@250A=6000W @ the Inverter (uncorrected).

I'd suggest Common-Port 200-250A Capable Smart-BMS, preferably Relay/Contactor. Passive Balancing does little on large cells such as these, but does help tweak Good Matched cells. I use an Active Balancer on all of my packs, which is a separate device.

The JBD Model with Relay is likely a Good Candidate, I've seen reviews & tests, looks good, they use TE Saver relays which is good.

* Chargery is not for everyone, there are new models coming which are one major step up but I'm not at liberty to discuss that at this time. Soon.
Active Balancers: I use QNBBM-8S' on my 5 production packs. The two Light duty ones, Heltec Capacitance Balancers.

In case you cannot see my Signature (apparently some don't see them) here's to my About My System pages. (I have to update to my final configuration)

Hope it helps.

Lately much negative news on Daly - there's posts about it on here.