Which JK BMS should I use for 24v, 8 cells LF280K?

[juha_teuvonnen]

I am building a 24v 280 Amp-hr battery bank by connecting 8 LF280K cells in series. I was told that JK BMS is the top quality option. I was also told that for 280 Amp-hr bank I need a 300 or 350 Amp BMS. I can't seem to find one from JK. Also, unsure if that would be 300-350 Amp max or sustained? The JK site seems confusing. I am new to LeFePO4 batteries, but not new to wiring and computer projects. A model number and a vendor to buy from would be very much appreciated.

I am looking at:
jk-b1a8s20p
jk-b2a8s20p

jk-b2a20s20p
jk-b2a24s20p

Will all of them work for my application?

 

[DIYrich]

Amps is dependent on your inverter. I have a 280 Amp battery with a 200 Amp jk bms (350 Amp peak). But it is one of 3 banks, with a combined max of 275 amps from all batteries that the inverter can take. Most of the time the one bank is 90 amps max. But if 2 batteries fail, the one can handle 275 amps for a short period.

 

[juha_teuvonnen]

Amps is dependent on your inverter. I have a 280 Amp battery with a 200 Amp jk bms (350 Amp peak). But it is one of 3 banks, with a combined max of 275 amps from all batteries that the inverter can take. Most of the time the one bank is 90 amps max. But if 2 batteries fail, the one can handle 275 amps for a short period.

If I wire 8 lf280K cells in series, they would be capable of producing approximately 280 amps at 27-28 volts? Is the BMS limiting the current, or is it the consumer? I have a wimpy inverter and very little use for 110v. I have a 750 watt 24 volt DC mini split AC and a 24 volt DC fridge that draws roughly 3 amps. Running the mini split and the fridge is the reason for building the battery.

 

[meetyg]

If you're looking for reliability, JBD/Overkill has been pretty reliable here on the forum.
There were some reliability issues with early models of the JK b2a8s20p, especially those with Heat port (for adding heat pads while charging below 0° C).
Personally, I have quite a few JBD models (mostly 4S, one 8S) and they are reliable (haven't had any failed yet).
But, the big downside to the JBD is passive balancing which is too weak.

That's why for my new build (2 x 8S 24v 90Ah) I went with the JK b2a8s20p (without Heat port).
I can't say much as my build is still in progress. What I do like about the JK (other than 2A active balancing) is that you can connect an external screen without giving up on Bluetooth. Also, it supports RS485 communication which helps connecting to software like Solar Assistant.

Keep in mind that for basically any BMS, you don't want to run it at it's rated load (200A for the JK) for prolonged times. This can cause heat buildup and premature failure.

But it sounds like for your use, you are way below that, so a 200A BMS should be fine, with room for expansion (larger inverter) in the future.

 

[740GLE]

If I wire 8 lf280K cells in series, they would be capable of producing approximately 280 amps at 27-28 volts? Is the BMS limiting the current, or is it the consumer? I have a wimpy inverter and very little use for 110v. I have a 750 watt 24 volt DC mini split AC and a 24 volt DC fridge that draws roughly 3 amps. Running the mini split and the fridge is the reason for building the battery.

So how is this all adding up to 300a at 24-28v of load?

I’d source a 200a BMS and possibly plan for a second battery if you feel the need.

Once you get up in current over 200a connections and heat are tough to keep in check.

 

[juha_teuvonnen]

If you're looking for reliability, JBD/Overkill has been pretty reliable here on the forum.
There were some reliability issues with early models of the JK b2a8s20p, especially those with Heat port (for adding heat pads while charging below 0° C).
Personally, I have quite a few JBD models (mostly 4S, one 8S) and they are reliable (haven't had any failed yet).
But, the big downside to the JBD is passive balancing which is too weak.

That's why for my new build (2 x 8S 24v 90Ah) I went with the JK b2a8s20p (without Heat port).
I can't say much as my build is still in progress. What I do like about the JK (other than 2A active balancing) is that you can connect an external screen without giving up on Bluetooth. Also, it supports RS485 communication which helps connecting to software like Solar Assistant.

Keep in mind that for basically any BMS, you don't want to run it at it's rated load (200A for the JK) for prolonged times. This can cause heat buildup and premature failure.

But it sounds like for your use, you are way below that, so a 200A BMS should be fine, with room for expansion (larger inverter) in the future.

Thanks for the info, I appreciate it. I suppose I can just disable the balancing feature, and use an active balancer instead? They are not very expensive, are there any downsides to using an external balancer? Overkill only carries 100 Amp BMS in 24 volt. Do you know if the quality issues with JK were resolved?

I am also wondering what is the difference between b2a8s20p and bd6a8s20p? Seemingly, the difference between b2a and b1a prefixes is balance current of 2 amps vs 1 amp. What does bd6 stand for?

 

[Horsefly]

Where did you see bd6a8s20p? I've not seen it, and when I look on the Hankzor store on Aliexpress, I can't find it. Are you sure?

 

[juha_teuvonnen]

Where did you see bd6a8s20p? I've not seen it, and when I look on the Hankzor store on Aliexpress, I can't find it. Are you sure?

These guys:

JK 3S-8S 200A 2A Balance Current Smart Active BMS

JK 3S-8S 200A 2A voltage collection, active large current balancing, overcharge, overcurrent, overtemperature protection, Coulombmeter.

srikobatteries.com

Oddly enough, the picture shows b2a8s20p, but the web site claims bd6a8s20p. I am totally confused as to what this mystery BMS actually is. I have a lingering suspicion it's a b2a8s20p.

 

[juha_teuvonnen]

So how is this all adding up to 300a at 24-28v of load?

I’d source a 200a BMS and possibly plan for a second battery if you feel the need.

Once you get up in current over 200a connections and heat are tough to keep in check.

I doubt that I will ever have a need for 200 amps. But I like overbuilding things when it doesn't cost me all that much.

 

[DIYrich]

These guys:

JK 3S-8S 200A 2A Balance Current Smart Active BMS

JK 3S-8S 200A 2A voltage collection, active large current balancing, overcharge, overcurrent, overtemperature protection, Coulombmeter.

srikobatteries.com

Oddly enough, the picture shows b2a8s20p, but the web site claims bd6a8s20p. I am totally confused as to what this mystery BMS actually is. I have a lingering suspicion it's a b2a8s20p.

Typo.

 

[meetyg]

These guys:

JK 3S-8S 200A 2A Balance Current Smart Active BMS

JK 3S-8S 200A 2A voltage collection, active large current balancing, overcharge, overcurrent, overtemperature protection, Coulombmeter.

srikobatteries.com

Oddly enough, the picture shows b2a8s20p, but the web site claims bd6a8s20p. I am totally confused as to what this mystery BMS actually is. I have a lingering suspicion it's a b2a8s20p.

I think the b2a is limited to 8s, while the bd6 or other models can be up to 20s.
I think that the b2a is a newer model than the rest (exists around 2 years).

The downside to having an external active balancer, is that it needs to be (manually) switched on only when cells are above 3.45v. Otherwise, it an actually mess up your top balance. Andy from Off-Grid-Garage @YT has shown this a few times.

There are "smart" active balancers from NEEY (also tested by Andy), but with the JK it's already built in, so it makes everything simpler to build and maintain.

My conclusion regarding reliability is that if you buy the JK from a known store on Aliexpress (Like Hankzor or HeltecBMS), get one without Heat port, and it's fairly recent model, reliability should be pretty good, given that you don't push it to its limits.

 

[740GLE]

I doubt that I will ever have a need for 200 amps. But I like overbuilding things when it doesn't cost me all that much.

I like over building too, over build with more storage, not higher current BMS.

Why have one battery when two will work just as good!!!

 

[BobR]

Amps is dependent on your inverter. I have a 280 Amp battery with a 200 Amp jk bms (350 Amp peak). But it is one of 3 banks, with a combined max of 275 amps from all batteries that the inverter can take. Most of the time the one bank is 90 amps max. But if 2 batteries fail, the one can handle 275 amps for a short period.

Google this:

JBD SMART BMS Lifepo4 Battery Balance 8S 12V/8S 24V/12S 36V 60A-200A w/Bluetooth​

 

[DIYrich]

Google this:

JBD SMART BMS Lifepo4 Battery Balance 8S 12V/8S 24V/12S 36V 60A-200A w/Bluetooth​

??? My comment to Juha is the amps out of the bank is dependent upon how much power the inverter needs. If he never needs more than 3kW, then a 200a bms is more than enough. If he needs the full 280 amps (6kW) for a full hour, then he needs a larger bms.

 

[Zwy]

I doubt that I will ever have a need for 200 amps. But I like overbuilding things when it doesn't cost me all that much.

300A at 24V = 7200W

7200W divided by 120V = 60A

I run my whole house on a pair of LV6548's which are 6500W each. I rarely use 4000 watts per inverter and that would be when running the electric dryer and the microwave at the same time.

There is a point of derating some Chinese sourced items. I have a 250A 24V Daly BMS in my truck camper and I originally derated it by 50%. I've never seen more than 2500W draw on the battery. Some China sourced items are proven to handle the rated capacity, JK, JBD are a few examples and I own some JBD. Overbuilding is fine but can lead to wasted money.

 

[Zwy]

I like over building too, over build with more storage, not higher current BMS.

Why have one battery when two will work just as good!!!

Yes, parallel batteries make life easier, less heat, easier sourced components and redundancy.

 

[juha_teuvonnen]

??? My comment to Juha is the amps out of the bank is dependent upon how much power the inverter needs. If he never needs more than 3kW, then a 200a bms is more than enough. If he needs the full 280 amps (6kW) for a full hour, then he needs a larger bms.

I didn't find a JK BMS that's more than 200 Amps sustained (300-350 amp peak). Is there a BMS that can handle sustained 280 amps at 24V? I am new to this, and I haven't found one. I don't mind spending a few extra dollars to get a system rated for more amps. Even if I never use the full capacity, a bigger BMS will handle my meager needs with ease.

 

[hwse]

These guys:

JK 3S-8S 200A 2A Balance Current Smart Active BMS

JK 3S-8S 200A 2A voltage collection, active large current balancing, overcharge, overcurrent, overtemperature protection, Coulombmeter.

srikobatteries.com

Oddly enough, the picture shows b2a8s20p, but the web site claims bd6a8s20p. I am totally confused as to what this mystery BMS actually is. I have a lingering suspicion it's a b2a8s20p.

They have misnamed it. the spec says it has 2A balancing so it is a b2a8s20p not a bd6a8d20p. d6 means decimal 6 or 0.6A active balancing. I personally prefer the 2A B2a8s20p

 

[hwse]

I didn't find a JK BMS that's more than 200 Amps sustained (300-350 amp peak). Is there a BMS that can handle sustained 280 amps at 24V? I am new to this, and I haven't found one. I don't mind spending a few extra dollars to get a system rated for more amps. Even if I never use the full capacity, a bigger BMS will handle my meager needs with ease.

JK makes the B2a25s60p which does 500A split-port with contactors. It can have protect currents up to 600A and +/- 500A continuous current.

 

[brianonmull]

Is it possible to successfully to create 2 8S EVE 280Ah based 24v batteries, and then series them to 48v, that is on the basis that I have 2 sets of active balancing going on at any one time 4A as opposed to 2A with a single JK 16s BMS.
Not sure of the rules here?