JBD BMS 48v, two in parallel, fuses?

[Swing]

TLDR: 48v li-ion NMC battery modules, why does JBD 3.7v bms 7s-20s descirption say that it is not good to parallel them, if I don't expect balancing currents higher than BMS can handle, protected with a fuse for each 48v module?

Long version:

Hi all, I have 2 times a 14s 10kWh block, it is NMC chemistry (so 3.7v nominal) They are rated 202Ah each.
I have one load which can pull up to 250A, peak power output. So that it is 0.625C for the whole pack, which is fine.

Now I would like to put a JBD BMS 200a or 300a on each battery module, as well as a 250A fuse for each block. I could add another 250A or 300A fuse where the positive lines come together, so that both modules will not deliver 500A in case of a short.

But the JBD BMS says in the description not to put them in parallel. This will have to do with high currents when one of them disconnects or reconnects (for example the temperature was too high and became lower again)

I realize there are better alternatives with CAN bus communicating slave modules and a master. However, it is much more cost effictive to put in two JBD BMSs.

The system is made as such it should never reach the limits of the battery modules.
However, it could still happen. If it does, a fuse of 250A could go out if the balancing current between the modules can be that high for a few seconds.
Next to the 250A fuse I could put like 150A DC breakers for easy resetting, but I don't really like them as they can burn out or burn fixed shut.

If I see youtube videos of what Will Prowse and others are building, they are often paralleling large amounts of 48v batteries, although typically LiFePo4, but the basic problem is the same.

Since this is an electric boat with NMC chemistry, things may be a bit different. If one module fails (bms disconnects) you still could reach the harbor on the remaining active battery module.

Thanks in advance.

 

[time2roll]

I agree with using a separate fuse for each BMS. Fuse rating can be close to the BMS rating and certainly correct to protect the wire. Max load by design should be max 80% of the BMS rating (together). JMHO.

If one disconnects under high load it will cascade to the other for full shut down. System design should be to avoid BMS disconnect in normal conditions. Carry extra fuse and prepare to reduce load to operate on one battery for critical systems.

 

[Denis]

TLDR: 48v li-ion NMC battery modules, why does JBD 3.7v bms 7s-20s descirption say that it is not good to parallel them, if I don't expect balancing currents higher than BMS can handle, protected with a fuse for each 48v module?

Long version:

Hi all, I have 2 times a 14s 10kWh block, it is NMC chemistry (so 3.7v nominal) They are rated 202Ah each.
I have one load which can pull up to 250A, peak power output. So that it is 0.625C for the whole pack, which is fine.

Now I would like to put a JBD BMS 200a or 300a on each battery module, as well as a 250A fuse for each block. I could add another 250A or 300A fuse where the positive lines come together, so that both modules will not deliver 500A in case of a short.

But the JBD BMS says in the description not to put them in parallel. This will have to do with high currents when one of them disconnects or reconnects (for example the temperature was too high and became lower again)

I've got the same BMS and I was also wondering if I could parallel them, I ordered two and paralleled them and are working really well, and I also have a 90 amps breaker on each banks. Six months after I added another 16s bank 280ah with another bms in parallel, and breaker, all is good.
If I work on one bank,I always make sure that all the banks are full charge and on float, before disconnect, and then once when I'm ready to reconnect the power I make sure the voltage is the same as the other banks. ( float voltage)
Never had any problems.

I realize there are better alternatives with CAN bus communicating slave modules and a master. However, it is much more cost effictive to put in two JBD BMSs.

The system is made as such it should never reach the limits of the battery modules.
However, it could still happen. If it does, a fuse of 250A could go out if the balancing current between the modules can be that high for a few seconds.
Next to the 250A fuse I could put like 150A DC breakers for easy resetting, but I don't really like them as they can burn out or burn fixed shut.

If I see youtube videos of what Will Prowse and others are building, they are often paralleling large amounts of 48v batteries, although typically LiFePo4, but the basic problem is the same.

Since this is an electric boat with NMC chemistry, things may be a bit different. If one module fails (bms disconnects) you still could reach the harbor on the remaining active battery module.

Thanks in advance.

 

[Swing]

I agree with using a separate fuse for each BMS. Fuse rating can be close to the BMS rating and certainly correct to protect the wire. Max load by design should be max 80% of the BMS rating (together). JMHO.

If one disconnects under high load it will cascade to the other for full shut down. System design should be to avoid BMS disconnect in normal conditions. Carry extra fuse and prepare to reduce load to operate on one battery for critical systems.

Yes I thought about choosing a BMS at 200A on purpose. Of course 300A would allow you to continue full power boating on the remaining module. However, I think it is a nice indication that something is wrong if you pull full power and it only does it for 10 seconds and then disconnect and reset. That way the user knows something is wrong, and one module has disconnected.

A fuse that pops, I could give one on the road, however, I would rarther have it that the user then has to come back for maintenance, or that we gp to the boat.
Because I am going to put a charger on each battery module, the boat can be plugged in to fully charge, and then replace the fuse.

A master slave can bus based bms would prevent all of this. However, it is so much more expensive.
The design is as such that the BMS should never intervine.

 

[Swing]

I've got the same BMS and I was also wondering if I could parallel them, I ordered two and paralleled them and are working really well, and I also have a 90 amps breaker on each banks. Six months after I added another 16s bank 280ah with another bms in parallel, and breaker, all is good.
If I work on one bank,I always make sure that all the banks are full charge and on float, before disconnect, and then once when I'm ready to reconnect the power I make sure the voltage is the same as the other banks. ( float voltage)
Never had any problems.

Thanks. Are you also using NMC? Or LiFePo4? Because internal resistance can be a bit different.