JK-BMS question?

[gray webber]

Hello folks.
I just received my JK-b2a24s20p BMS that I hopped would do the job for my 8s 280ah pack. If course it came without a manual so I did the search and found two conflicting options???
1-it will not work on an 8s so needs to be returned and get a b2a8s20p? The Bangood site lists it as an 8s-24s but no paperwork confirming this and after watching Off Grid Garage, it may be one that only works from 14s to 24s?
2-it will work but without manual to make certain I do not fry it I should keep searching?
Suggestions?
Thanks.

 

[NVS]

These is not for 8s configuration.

Active balancer BMS - JK BMS

Below bluetooth active balancing BMS also support RS485/CANBus for optional are available for sell: JK-BD6A17S6P JK-BD6A20S6P JK-BD6A24S6P JK-BD6A20S10P JK-B1A24S15P JK-B2A24S20P The above

www.jkbms.com

 

[Nami]

These is not for 8s configuration.

Active balancer BMS - JK BMS

Below bluetooth active balancing BMS also support RS485/CANBus for optional are available for sell: JK-BD6A17S6P JK-BD6A20S6P JK-BD6A24S6P JK-BD6A20S10P JK-B1A24S15P JK-B2A24S20P The above

www.jkbms.com

this is not JK-BMS offical website

 

[gray webber]

I have built my 8s 280ah EVE battery using a JK 8s20p BMS. It seams to be working well.
The BMS came without a manual of any kind. I accessed Aliexpress to find the wiring info.
Now I hear from Off Grid Garage video that the JK does not support parallel battery builds?????? So if I want to double my battery storage I would have to find a different BMS???? Anyone have answers like . Is it true no parallel battery build?
If so, what BMS would be good to go to?

 

[740GLE]

Andy is running a JK 16s, JBD 16s and a QUCC 16s BMS in his 48v bank. I can’t imagine why a JK BMS can’t run in parallel, assuming load isn’t crazy high.

 

[rhino]

There is this thread discussing that confusing statement about not being able to parallel them which doesn't make sense to me: https://diysolarforum.com/threads/jk-4s-200a-bms.38623/post-511179

 

[hwse]

I have built my 8s 280ah EVE battery using a JK 8s20p BMS. It seams to be working well.
The BMS came without a manual of any kind. I accessed Aliexpress to find the wiring info.
Now I hear from Off Grid Garage video that the JK does not support parallel battery builds?????? So if I want to double my battery storage I would have to find a different BMS???? Anyone have answers like . Is it true no parallel battery build?
If so, what BMS would be good to go to?

Sorry, I am the one who got this whole question started and @Nami is saying that paralleling full batteries each protected with a JK BMS is in her words and capitalization "NOT RECOMMEND" in post #75 of the thread that rhino linked to above.

It is the craziest thing I have ever heard. Her contention is that no BMS of any manufacture other than Daly (using there Parallel "sports car brick" can be used in parallel. [Nami post #67 "Currently only one SP04S028A for JBD can support concatenation. For daly, only the new Configuration Parallel Module supports the use of Parallel PACK. I know these products very well. For the sake of battery safety for all users, we do not recommend parallel use. Thank you. We are considering..."

I suspect it is a misunderstanding of the usage or miscommunication between her and the engineers at JK but I cannot imagine that this is actually true. There is just too much "real-world" experience of successful installations out there. In looking at what the Daly Parallel Module does, it appears that the concern is about the in-rush current that will happen when two batteries are connected with different resting voltages. This can be completely overcome by bringing each battery to the same voltage before connecting in parallel. In real world testing (Andy) even when there is significant difference in voltage, the current being transferred is really not all that high because of the flat charge curve on the LFP cells.

 

[DThames]

Sorry, I am the one who got this whole question started and @Nami is saying that paralleling full batteries each protected with a JK BMS is in her words and capitalization "NOT RECOMMEND" in post #75 of the thread that rhino linked to above.

It is the craziest thing I have ever heard. Her contention is that no BMS of any manufacture other than Daly (using there Parallel "sports car brick" can be used in parallel. [Nami post #67 "Currently only one SP04S028A for JBD can support concatenation. For daly, only the new Configuration Parallel Module supports the use of Parallel PACK. I know these products very well. For the sake of battery safety for all users, we do not recommend parallel use. Thank you. We are considering..."

I suspect it is a misunderstanding of the usage or miscommunication between her and the engineers at JK but I cannot imagine that this is actually true. There is just too much "real-world" experience of successful installations out there. In looking at what the Daly Parallel Module does, it appears that the concern is about the in-rush current that will happen when two batteries are connected with different resting voltages. This can be completely overcome by bringing each battery to the same voltage before connecting in parallel. In real world testing (Andy) even when there is significant difference in voltage, the current being transferred is really not all that high because of the flat charge curve on the LFP cells.

I use the JBD BMS and with the phone app you can turn the battery output off. So you can monitor two or more BMS and then when you get the bus (already connected and active battery(s)) voltage to match the additional battery voltage, turn on that battery with next to zero voltage difference. Procedure is to turn off all batteries output, connect the power wiring, determine if you want to charge or to discharge to make bus adjustments. Bring first battery (highest or lowest) on, then adjust the bus toward the next battery that you want to connect.

 

[hwse]

I use the JBD BMS and with the phone app you can turn the battery output off. So you can monitor two or more BMS and then when you get the bus (already connected and active battery(s)) voltage to match the additional battery voltage, turn on that battery with next to zero voltage difference. Procedure is to turn off all batteries output, connect the power wiring, determine if you want to charge or to discharge to make bus adjustments. Bring first battery (highest or lowest) on, then adjust the bus toward the next battery that you want to connect.

That is what I have always assumed to be the correct method but with the seller saying "NOT RECOMMENTED", it makes you wonder. I suspect that this is not the bid deal that Nami is making it out to be but am not happy about the seller saying an emphatic NO!

 

[rhino]

If I am understanding what the concern is; using example of 2 battery banks using 2 separate BMS's:
- battery #1 has very low SOC and BMS has battery cut off for whatever reason
- battery #2 is full and BMS is active
- BMS #1 turns back on and there would be nothing besides the BMS itself limiting the amount of current being dumped back into battery #1 from battery #2

Is that the issue?

 

[NVS]

I can see why they don't recommend connecting them together. The charge current the bms is rated for can easily be exceeded by in rush current from another battery. I think if you have 2 battery banks that are fully charged it would be safe to connect them.

Bad design:
If you design a system that uses 175amps to run and can charge at 80amps. So you put two 100amp battery banks to get 200amp capacity and 100a charge capacity. If one bank fails or faults you now have 1 bank trying to supply 175a or charging at 80a. Both of which is more than 1 bank can handle.

Good design.
All banks and bms can handle the needed supply current and charge current. So no problem if one bank shuts down.

 

[DThames]

Just an application note......I built up two 36v Li-ion batteries with a BMS on each one, in parallel. I was testing it to see what happens when the batteries are at a low state of charge and because of current demand, a cell voltage drops enough to trigger BMS cutoff. The first one shut off and then right away the second one did. I got it back to the house and when put on a charger only one of the BMS came back on to start taking a charge. I spotted this right away because I was watching to see what would happen. I shut charging off, shut off the battery (in the BMS software) and started charging again. The second battery now started taking a charge. I got them both back to the same voltage before turning both on at the same time. So, yes, for those not equipped to manage such a setup, this would not be an ideal solution. (two independent BMSs on the same load)

 

[gray webber]

Wow! So what BMS do all these battery manuf use? Most say ok to 4p and 2s or 4s.
They all have a BMS built in. They have no issue figuring a good design to manage both series and parallel connections. With warrantees from 1-10 years!
I could imagine issues with series due to internal resistance and voltage imbalance but parallel does not bring the voltage issue. If both are close in resistance then current imbalance should also be small and one BMS should stop charging when voltage is reached and the second would continue till it’s voltage is reached?
Could the SOC get out of balance? Yes but if full charge is set up to be the same on both batteries then each time a full charge is reached the imbalance is removed (reset).
My thought is that after a long time if batteries are not brought to full charge then one will work harder then the other and SOC will get out of balance.
Solution? Frequent full charges and same voltage settings on both BMS?????
Thoughts????

 

[Nami]

Wow! So what BMS do all these battery manuf use? Most say ok to 4p and 2s or 4s.
They all have a BMS built in. They have no issue figuring a good design to manage both series and parallel connections. With warrantees from 1-10 years!
I could imagine issues with series due to internal resistance and voltage imbalance but parallel does not bring the voltage issue. If both are close in resistance then current imbalance should also be small and one BMS should stop charging when voltage is reached and the second would continue till it’s voltage is reached?
Could the SOC get out of balance? Yes but if full charge is set up to be the same on both batteries then each time a full charge is reached the imbalance is removed (reset).
My thought is that after a long time if batteries are not brought to full charge then one will work harder then the other and SOC will get out of balance.
Solution? Frequent full charges and same voltage settings on both BMS?????
Thoughts????

If parallel battery packs are required, the same voltage can reduce the chance of failure.
But it's hard to do.
Or add a discharge diode in each battery pack, which is the way we're currently considering

 

[gray webber]

If parallel battery packs are required, the same voltage can reduce the chance of failure.
But it's hard to do.
Or add a discharge diode in each battery pack, which is the way we're currently considering

Where would the diode be placed? High power type?

 

[Nami]

Where would the diode be placed? High power type?

Since BMS is usually the same port for charging and discharging,
You need to change the link order of your BMS
The charger at the charging end is connected before the diode,
Load at discharge end is connected behind diode

 

[gray webber]

Since BMS is usually the same port for charging and discharging,
You need to change the link order of your BMS
The charger at the charging end is connected before the diode,
Load at discharge end is connected behind diode

Thanks for providing that but I’m a novice and do not follow your recommendation.
Any chance of a schematic?
Thank you!

 

[Nami]

Thanks for providing that but I’m a novice and do not follow your recommendation.
Any chance of a schematic?
Thank you!

We're still experimenting and testing,
There is no accurate reply yet,

 

[Kuy Bicol]

Hello folks.
I just received my JK-b2a24s20p BMS that I hopped would do the job for my 8s 280ah pack. If course it came without a manual so I did the search and found two conflicting options???
1-it will not work on an 8s so needs to be returned and get a b2a8s20p? The Bangood site lists it as an 8s-24s but no paperwork confirming this and after watching Off Grid Garage, it may be one that only works from 14s to 24s?
2-it will work but without manual to make certain I do not fry it I should keep searching?
Suggestions?
Thanks.

So I have the JK-B2A24S15P BMS, and am using it on 16x EVE 280AH cells configured in 2P8S 24V system. It is working in 8S configuration, new system build, running for about a month now. After installing the mobile app and connecting for the first time, it detected that cells didn't match with the pre-configured 16 cells but I was able to adjust down to 8 cells, and also adjusted few other parameters.

This JK-BMS is great in my opinion, I was able to top balance the newly installed pack just by using the integrated 2A balancer. So it works at 8S and I assume it's going to work also at 24S and everything in between. Hope this helps.

 

[Nami]