Connecting JKBMS in parallel

[Familymandan]

Hello, I did my own solar system design and install. I have 48VDC.
Batteries: LiFePO4, 3 separate banks of 3.2VDC x 16 in series. 272 ah each. On each battery I have installed JK B2A24S15P BMS.
All 3 banks/BMS are in parallel wired to +/- bus bars.
I have 5 charge controllers, also in parallel, each wired to +/- bus bars.
I have a Sigineer 12kW inverter, also wired to the same +/- bus bars.
All of the + are tied together, all the - are tied together.
My purpose of 3 banks is to increase the Amp Hours of storage
My question(s):
Do I have to do anything to the BMS to make them work in parallel? Programming, wiring....?
I don't see any setting in the software to set a slave/master...
Will each BMS charge/discharge from it's own battery bank as it needs, not caring about the other 2?
I want them to charge/discharge relatively evenly with one another.
Do I have to do anything different to get all 3 banks to work as a 48VDC - 816ah battery?
I previously used (3) Daly BMS systems in the same manner and the system only used 1 of the battery banks. It would charge/discharge from the same bank every time. Never even looking at the 2nd/3rd bank. The inverter voltage would read the voltage from the 1st bank only. The other 2 could be full but if the 1st battery was low, game over.
Questions/comments???

 

[TacomaJoe]

The BMS takes care of its cells and isn't aware of the other batteries. In parallel, the batteries will share the load/discharge currents equally, giving you 816Ah of capacity.

Not sure what was up with your Daly. Again, tied in parallel they should share the load. A guess would be that two of them shut down (went to sleep) or something. I have 3 JBD BMS on my bank. I have seen one shut down on cell over voltage at the top of the charge cycle, but it only stops the charge side, it will still share the load on the discharge side.

 

[Familymandan]

The BMS takes care of its cells and isn't aware of the other batteries. In parallel, the batteries will share the load/discharge currents equally, giving you 816Ah of capacity.

Not sure what was up with your Daly. Again, tied in parallel they should share the load. A guess would be that two of them shut down (went to sleep) or something. I have 3 JBD BMS on my bank. I have seen one shut down on cell over voltage at the top of the charge cycle, but it only stops the charge side, it will still share the load on the discharge side.

That is good news. Thank you. I read to install a class T 125A fuse in each BMS circuit. Does it matter if it is on the + or -?

 

[S Davis]

That is good news. Thank you. I read to install a class T 125A fuse in each BMS circuit. Does it matter if it is on the + or -?

Fuse on positive of battery, BMS is on negative of battery.

 

[Familymandan]

Fuse on positive of battery, BMS is on negative of battery.

Totally makes sense. Thank you S.

 

[jeff164]

I…

 

[kommando]

Its a JK BMS with known failures as do most BMS's, you need a fuse.

 

[jeff164]

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[Familymandan]

I don't have first hand experience with an issue NOT having a fuse. But, I say, it can't hurt and may help.

 

[Familymandan]

I have another question. As stated at the beginning of this thread, I have the (3) BMS in parallel. No issues enabling charging/discharging when all 3 connected to the (5) charge controllers. When I connect the + and - of my inverter and turn the BMS Discharge on, I immediately get a "Protection (Discharge Short Circuit) error. It happens on all 3 BMS. Only when I connect the inverter. I def have it connected to the correct + and -. Even if the inverter is OFF. I have noting connected to the input OR output terminals on the inverter. Is there a setting on the JKBMS?

 

[jeff164]

!

 

[upnorthandpersonal]

Still not convinced I need a fuse.

You need a fuse. Like this:

JK 4S 200A BMS

If parallel battery packs are required, the same voltage can reduce the chance of failure, But it's hard to achieve, Or add a discharge diode in each battery pack, which is the way we are currently considering How is the same voltage hard to achieve? 90% of the charge curve is at the same...

diysolarforum.com

If you have multiple packs in parallel, and something goes wrong with one pack, the rest can dump their current into this pack. Imagine the following:

- Something is wrong with one BMS (it happens) and something happens in the pack
- Imagine three others in parallel with this, just fine.
- Each BMS can handle 200A.
- Because something is wrong with one of the packs, it starts drawing current from the others (not a dead short)
- Each parallel pack contributes 150A (well below their rating, so they don't shut off)
- The pack with the issue now gets 450A dumped into it and the BMS can't turn it off.

 

[mikefitz]

Still not convinced I need a fuse.

It's standard electrical practice to install overcurrent protection. Adding fuses and breakers to systems is not optional, its necessary for safety. It's probable your system is in a dwelling , for your safety and the safety of others please follow best practice.
Have a look at this section on the forum,

Up in smoke... learn from my mistake!

Did your experimental battery or home built inverter experience a rapid, unplanned disassembly? Reverse polarity a $3K inverter, and see it go up in smoke? Share it here!

diysolarforum.com

 

[jeff164]

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[jeff164]

2

 

[upnorthandpersonal]

The BMS does already have electronic over current protection built in, and I do consider using this feature a safe electrical practice.

It's still something that can fail. A MOSFET (the thing in a BMS that interrupts the current) most often fails closed. Put a fuse. It's a minor thing that might save you from major headaches, even with a smaller battery set-up.

 

[jeff164]

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[Partimewages]

@jeff164
I doubt the people that have had fires would agree with you. You get no do overs with a fire!

 

[upnorthandpersonal]

The MOSFETs in the BMS are not an electronic fuse. But it seems you've made up your mind, so best of luck!

 

[jeff164]

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[jeff164]

,

 

[Partimewages]

You won't be alive to write about it

 

[jeff164]

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[Familymandan]

The inverter has some very large input capacitors on the battery line. You will need to pre-charge these capacitors using a suitable resistor before turning on the BMS.

Using a jumper with one end connected to the resistor bypass the BMS untill caps are charged. It is a smart idea to connect alligator clips to both ends of your jumper for a safe one hand operation…

Usually this is done by bypassing the battery B+ disconnect switch. The resistor wills allow the capacitors to charge at a slower rate.



Remember to use extreme caution, 48 volts and above is enough voltage to overcome the bodies resistance. If that voltage goes between your right and left hand it has the possibility to stop your heart dead!

So this is a 1st time only thing? What size resistor? (Wattage/ Volts). Where do I connect the resistor to exactly? How many amps will be flowing?

 

[jeff164]

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