JBD 4S 200A BMS in Parallel

[KaFun]

...
The problem comes to if it will shut down immediately or cause damage before it shuts down to the second BMS and that's the part I don't know and truthfully the Chinese manufacturers probably don't know either
...

There's a general problem I had to encounter unfortunately (independent of paralleled batteries):
When charging my batteries with a solar MPPT charger and the (last) BMS decided to switch off because the battery was fully charged, there had been a voltage spike destroying my inverter input circuitry.

My thesis is as follows:
As the MPPT charger is a buck converter, it consists of at least one heavy inductor. And an inductor doesn't like to be switched off when in full swing. If it is nevertheless, this leads to VERY high voltages (this effect had been used effectively for decades in car ignition systems). On the bright side, I can report that no BMS ever gave in (even not the ones that already had switched off).

So as a result I now make sure that the solar charger switches off below the BMS "trigger" voltage, i.e. the solar charger "Over voltage disconnect" has to be lower than the "sum volt high level 2" entry in the DALY software.

Furthermore make sure, there is no inductor somewhere in your setup (remember a coiled up surplus cable is already an inductor).

Coming back to switching off BMS under heavily load: As an inverter also uses inductors, it also might not like radical changes in current. But this holds true also for system using just a single battery.

So I have to agree with ericfx1984 and ereams65 ... BMS manufacturers just go on the safe side because they probably didn't went through the effort of testing it.

 

[Maintenance guy]

I see large Lithium battery bank units being stacked in racks with each having separate BMS then a total system monitor all the time on many video's. i have never heard of them experiencing problems like are being discussed on many threads. i agree with Kafun that the manufactures are just to lazy to test it as all they care about is quick money.

I will be building a power wall with (13) 48 volt 32ah modules each with it's own BMS. each module is capable of supplying 400 amp continuous. adding a APT2X61S20J Schottky Diodes in a SOT-227 package on heatsink on positive side with 60 amp Circuit breakers between the BMS and main busbar. i then will have a 400 amp main disconnect between the busbar and inverter/charger.

total system amperage for the 12K split phase inverter charger is 330 amp yet each BMS will only supply 26 amp with everything on in the house which is not going to happen. i am leaning towards using 60 amp BMS's. even if by some remote chance i have a disaster happen (7 down) 6 BMS's can still handle the load which by the way would never happen. each connection between modules and busbar will be matched ohm wise.
I will of course be posting on my entire build.

 

[KaFun]

Interesting project! If I understand correct, you'll have 13 separate battery systems, each 48V 32Ah connected in parallel. What I have trouble understanding is what you're doing with the diodes. If you put them on positive side of the each battery, then you allow each battery only to discharge (or charge if you put the diode in reverse). So I do not understand how this should work as a battery bank that shall be charged and discharged preferably at the same time.
If you're able to control the BMS (see my post here), you can leave the diode out as the BMS can take care of that, i.e.disabling unwanted back and forth charging between individual batteries ... if this would be a problem after all.

There is another reason why being able to control charge/discharge of each battery can be important: in the hopefully unlikely event of a BMS failure in which it shorts internally, all batteries would "contribute" to a pretty hefty heat up if the individual fuses are not being chosen carefully. In that case, by switching off all other BMS at once, the damage might get contained.

However, if you spend two diodes per BMS, you can create a charge rail and a discharge rail. In that case you do not have to worry about any short in an individual BMS as it would only "absorb" all of the charging current at the moment of failure. The remaining batteries would just "experience" a stop in charging but continue to supply power to your inverter. However at the cost of up to 54W power loss per diode (your Schottky diode has a Vf of 0.83V @ 60A = 54W). And you'll have losses also during charging ...

Looking forward to your thoughts and ideas!

 

[Maintenance guy]

Interesting project! If I understand correct, you'll have 13 separate battery systems, each 48V 32Ah connected in parallel. What I have trouble understanding is what you're doing with the diodes. If you put them on positive side of the each battery, then you allow each battery only to discharge (or charge if you put the diode in reverse). So I do not understand how this should work as a battery bank that shall be charged and discharged preferably at the same time.
If you're able to control the BMS (see my post here), you can leave the diode out as the BMS can take care of that, i.e.disabling unwanted back and forth charging between individual batteries ... if this would be a problem after all.

There is another reason why being able to control charge/discharge of each battery can be important: in the hopefully unlikely event of a BMS failure in which it shorts internally, all batteries would "contribute" to a pretty hefty heat up if the individual fuses are not being chosen carefully. In that case, by switching off all other BMS at once, the damage might get contained.

However, if you spend two diodes per BMS, you can create a charge rail and a discharge rail. In that case you do not have to worry about any short in an individual BMS as it would only "absorb" all of the charging current at the moment of failure. The remaining batteries would just "experience" a stop in charging but continue to supply power to your inverter. However at the cost of up to 54W power loss per diode (your Schottky diode has a Vf of 0.83V @ 60A = 54W). And you'll have losses also during charging ...

Looking forward to your thoughts and ideas!

What really bothers me is the losses used with the diodes as that adds to 700 watts loss. this is not acceptable by any means. i plan on top balancing then installing the BMS so everyone will be balanced and full when installed in system. with the cells being rather new i see no imbalance happening soon.
I like the control of the BMS better then the diode idea and yes i am choosing the fuses or circuit breakers wisely in case of disaster.
i have also considered two stacks of 60280's @ 64 each but then i would have to purchase a crap load of copper plate around 1 grand worth plus very hefty BMS's. i just like the pre built one's in the previous post that will save a grand plus.
so what is your thought on separate charge discharge BMS lines verses same line.? i am leaning towards separate.

 

[KaFun]

You write "with the cells being rather new i see no imbalance happening soon." - this I would not bet too much on! If you do not cycle your batteries all the way through, i.e. also allow for full charging following by balancing (DALY BMS is supposed to balance cells as well), this will not work out. I have batteries running for almost a year basically floating on a solar charger. In summer, this is not problem as they get fully charged up, but right now, two of my three batteries ended up with cell2cell differences of more than 300mV simply because the battery did not reach balancing level before the sun went down again. So there is need for grooming ...

And regarding separate lines for charge/discharge: This can only be realized with your additional diodes and hence implied losses. So that is no option for me at least.

 

[Maintenance guy]

The 12K split Phase inverter/charger i will be using states it is off grid meaning no feed back but it does have a feature that allows grid utility to be connected as back up. if the solar panels are to week to charge the batteries the inverter will allow the grid utility to charge them and supply house.
so basically using the grid utility as backup only allowing the batteries to get fully charged all the time.

this is an awesome feature to me plus the inverter/charger has automatic generator startup plus two MPPT charge controllers that allow different string voltages and amperages. with that in mind the inverter/charger allows combination charging ie.. grid utility and MPPT solar simultaneous charging.

to me it is worth the 25 buck utility connection fee per month if solar fails in winter as i am still covered yet never used in summer.

 

[KaFun]

Yes, this is a great feature. Unfortunately, in Germany, utility provider do not allow for such systems to be installed.

 

[Maintenance guy]

How sad and pathetic on their part. greedy companies must be broken.
in the US in the state i live in they want a blueprint of the system because they thought it was grid tie. so i explain to the dumb guy the system is NOT grid tie so no feed back into the grid using only for backup so now i need NO blueprint for installation. i am installing the system myself then having a qualified electrician check it over then christen it.

 

[Just John]

I think the JBD is more dependable than Daly.

I own both. I can confirm from actual experience the JBD is more dependable.

 

[Just John]

The manufacturer rep said only the JBD 50a to 100a BMS's worked in series or parallel. Looks like I'll be reselling 3 200a BMS's. Eventually, I will be rebuilding to 24v or 48v where this won't be a problem, however, that requires replacing my $1000 inverter. Maybe next year.

I know the 150 amp models work fine both in series and parallel.
I would have no qualms with hooking up the 200 amp models in parallel, but not in series.

I wouldn't sell those BMS until you have tested that. I'll probably be testing it soon myself. But I expect no problems.

 

[DENWA]

Just to clarify my understanding of everyone's terminology.

Parallel BMS meaning they have 2 BMS connected to the SAME set of Cells. this causes an issue as 200Amp draw may not be split evenly between them and would never be practical.

Parallel Batteries are two independent sets of BMS's and cells, whose outputs are combined in Parallel (~100A + 100A = 200A @ 12V). This is OK as each BMS can regulate its output independently as it was intended.

Series BMS meaning they have 2pcs of 4S BMS in a pack to make an 8S BMS. Bad idea as current would have to flow through both and it would be a mess!

Series Batteries meaning they have two independent sets of BMS's and cells, whose outputs are combined in Series (~12V + 12V = 24V @ 100A). this is really a function of the Voltage ratings on the BMS MOSFETS if they can handle the peak Vds.

 

[RCinFLA]

There are many batteries that do not allow parallel configurations. It has to do with backfeed I think.

Usually, there is a limit number in place, like, no more than 4 in parallel, or, all in parallel must be identical specs. I do not remember.

Most 'dual port' BMS with separate load and charger inputs cannot be paralleled. They accomplish the two separate ports by just splitting the normally back to back MOSFET's. This allows current to flow backwards through MOSFET body diodes so a parallel battery could back feed current into the other battery array dual port BMS.

Should just stay away from dual port BMS's.

 

[RCinFLA]

Problem with paralleling two BMS's to achieve higher current is each BMS has a tolerance range to their shut down trigger points. One BMS may shut down before the other putting all the current on the remaining BMS.

Multiple battery packs with individual BMS's should have inter-BMS communications so if one BMS shuts down, they all shut down. Some individual BMS's with CAN or RS485 Mod bus communications can do this.

 

[Maintenance guy]

"Multiple battery packs with individual BMS's should have inter-BMS communications so if one BMS shuts down, they all shut down. Some individual BMS's with CAN or RS485 Mod bus communications can do this."

This is why people are running into trouble because of lack of research on products. these are must have features in my book. all one has to do is ask for Inverter RS485 specs spec sheet then either buy one to match protocol or talk with BMS manufacture to align RS485 specs which is what i did.
end result, inverter talks to all BMS and displays right parameters.

 

[Kerry downunder]

If I have 2 JBD 200a in paralle, will that allow the system to handle an inverter with a 284a requirement?

 

[Just John]

If I have 2 JBD 200a in paralle, will that allow the system to handle an inverter with a 284a requirement?

There is a lot of "it depends" for any accurate answer. More details would allow an answer.
For instance, if you are talking about two in parallel on a single set of 100 amp hours cells, probably not.

 

[Maintenance guy]

You can of course contact these people and order a BMS that can handle your requirements. https://www.lithiumbatterypcb.com

I have talked to them and they seem willing to accommodate just about anything. I am sure they make a 300A BMS using a relay just not sure it is for 12 volt. please contact them to avoid the parallel issues. I looked and they redesigned their relay BMS that is no longer external. it is now built under the aluminum heat shield which is very nice indeed.

PS I know one of their relay BMS's can handle 600A peak. I am also buying their 48 volt 900 watt bat charger for LiFePo4 system.
Regards,
Maintenance Guy

 

[A.Justice]

You can of course contact these people and order a BMS that can handle your requirements. https://www.lithiumbatterypcb.com

I have talked to them and they seem willing to accommodate just about anything. I am sure they make a 300A BMS using a relay just not sure it is for 12 volt. please contact them to avoid the parallel issues.

I've ordered five different BMS's from them. They answer questions quickly, and everything I've ordered from them functions and looks exactly as advertised. Highly recommend.

 

[Maintenance guy]

Excellent , I even think they will work with you on CAN protocol so it can communicate with your Inverter. I really like this company so far and am very impressed. I even talked to them about adjusting LiFePo4 battery charger down to stay out of the knee and I was told that there is a voltage adjustment pot on the board. wow is all I said.

 

[bryn]

If I have 2 JBD 200a in paralle, will that allow the system to handle an inverter with a 284a requirement?

The answer is yes, if i recall you have 280ah cells?

The issue you may have is if one of the BMS's shuts down and dumps the entire load on one BMS.

Im running 2 of these BMS, with 12 volt 304 ah packs, splitting the load.

I've set up restrictions to reduce the load to no more than 200ah as my main reason was to have 2 independent systems while one the road in case one started play up.