What size BMS do I need for a multiple BMS system?

TommyHolly

Solar Enthusiast
Joined
Jun 24, 2021
Messages
193
As I've said before in this thread, I can't recommend Daly.
I'm glad to answer questions.
Not glad to repeat myself.
The previous owner had a QNBBM Lithium Battery Balancer attached to each and every cell in his system. It was 4 cells in series making 12v and then 12 batteries in parallel making 1,200Ah.

Should I use these in my 3P 4S battery system? Or is that the job of the Overkill 120A BMS that I purchased?
 

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TommyHolly

Solar Enthusiast
Joined
Jun 24, 2021
Messages
193
One BMS for each battery and they do not need to communicate with each other in any way. Each battery with its BMS is a separate system.

I just bought two JBD BMS’s exact same unit as the Overkill from Current_Connect, minor issue with the order on pre shipping, JBD shipped the wrong cell sense wire with the BMS so shipping was delayed a bit. Current_Connect was very informative and fixed the issue, response to calls was fast and informative. I am happy with the way they deal with customers.

My system is 24 volt with 2 seperate banks of 2P8S LFP pouch cells @ 200 amps per bank so you will be using a different BMS but very similar.

Post a pic of your boat, I only got sail my Brown for a few years
The previous owner had a QNBBM Lithium Battery Balancer attached to each and every cell in his system. It was 4 cells in series making 12v and then 12 batteries in parallel making 1,200Ah.

Should I use these in my 3P 4S battery system? Or is that the job of the Overkill 120A BMS that I purchased?
 

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Tecnodave

Solar Addict
Joined
Mar 22, 2021
Messages
761
Absolute use the QNBBM Active balancers in parallel with the BMS on each battery The BMS does a small amout of passive balancing using resistors to burn off excess power from each cell but the Active balancers actually move power form the more charged cells to the cells with less charge. One thing very important is to hook up all the cell wires first, then verify the correct voltage appears on the correct terminal in the correct order 0v, 3.2v, 6.4 v, 9.6v 12.8 v before plugging in the BMS and Balancers. Do this on every cable that plugs into each balancer and each BMS, Having the wires connected in the wrong order will instantly release the magic smoke smoke from the balance or BMS.

I am doing the same thing with very similar BMS and balancer, my system is a bit different as it is 2P 8S in each battery pack. I will end up with 2 each 24 volt batteries at 200 a.h.

I am using the same manufacturer BMS but supplied by current_connect instead of Overkill but the manufacturer is JBD for both brands and using Active balancers made by Heltec which are probably not as good as the QNBBM but I obtained my cells for nearly free but they are of unknown, untested quality.

At hookup time I will have a chart ready with all the leads identified and listed with all the expected voltages at each pinout. Sort of a check list with check off boxes for each wire. As i have 8 “cell packs” in each battery I will have 9 sense and balance wires on each battery for a total of 18 wires to each pack, one wire in the wrong location and i will be making magic smoke of my investment. check, verify,check,verify.....

Im using “pouch cells” which are what is inside each “prismatic cell” but no poster on this forum and 3 other forums has admitted to seeing anything like this. my pouch cells were removed from a “powerwall” deemed not suitable for the intended application.

Sorta out on the front lines with this one. I may well end up purchasing prismatic cells. this is a learning venture, been using FLA for many years now. currently Im using L-16 format FLA battery from Rolls Surette 6 volt 400 a.h. 4 in series for 24 volt system now 16 3/4 years old.....AND a second set L-16 FLA , US Battery 24 volt 426 a.h. now 17+ years old.. about 24 kw. total capacity as my main banks with 2 Midnite Classic 150 controllers and 4800 watts panels

Can I come down there for a sail? just wishing, really loved getting out there in the middle of stuff, my trimaran could easily run away from the storms as with a 31 foot boat I really did not want a confrontation with huge seas.

Pilots say “keep the blue side up” with sailing its the other way around. Your cat must be about 64 feet.

Here are some pic’s of pouch cells mounted in plastic frames, I have made compression frames with plywood and threaded rod as some posters on this forum have talked about....

The the iCharger you see in one pic does some of the functions of a BMS but it does not have cutoff capability , it is doing monitoring now but I can charge, discharge batteries with this device, sort of a testing setup....really meant for electric model aircrafters.....I started with very small packs of LiPo and LiLo batteries for experience.
 

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TommyHolly

Solar Enthusiast
Joined
Jun 24, 2021
Messages
193
Absolute use the QNBBM Active balancers in parallel with the BMS on each battery The BMS does a small amout of passive balancing using resistors to burn off excess power from each cell but the Active balancers actually move power form the more charged cells to the cells with less charge. One thing very important is to hook up all the cell wires first, then verify the correct voltage appears on the correct terminal in the correct order 0v, 3.2v, 6.4 v, 9.6v 12.8 v before plugging in the BMS and Balancers. Do this on every cable that plugs into each balancer and each BMS, Having the wires connected in the wrong order will instantly release the magic smoke smoke from the balance or BMS.

I am doing the same thing with very similar BMS and balancer, my system is a bit different as it is 2P 8S in each battery pack. I will end up with 2 each 24 volt batteries at 200 a.h.

I am using the same manufacturer BMS but supplied by current_connect instead of Overkill but the manufacturer is JBD for both brands and using Active balancers made by Heltec which are probably not as good as the QNBBM but I obtained my cells for nearly free but they are of unknown, untested quality.

At hookup time I will have a chart ready with all the leads identified and listed with all the expected voltages at each pinout. Sort of a check list with check off boxes for each wire. As i have 8 “cell packs” in each battery I will have 9 sense and balance wires on each battery for a total of 18 wires to each pack, one wire in the wrong location and i will be making magic smoke of my investment. check, verify,check,verify.....

Im using “pouch cells” which are what is inside each “prismatic cell” but no poster on this forum and 3 other forums has admitted to seeing anything like this. my pouch cells were removed from a “powerwall” deemed not suitable for the intended application.

Sorta out on the front lines with this one. I may well end up purchasing prismatic cells. this is a learning venture, been using FLA for many years now. currently Im using L-16 format FLA battery from Rolls Surette 6 volt 400 a.h. 4 in series for 24 volt system now 16 3/4 years old.....AND a second set L-16 FLA , US Battery 24 volt 426 a.h. now 17+ years old.. about 24 kw. total capacity as my main banks with 2 Midnite Classic 150 controllers and 4800 watts panels

Can I come down there for a sail? just wishing, really loved getting out there in the middle of stuff, my trimaran could easily run away from the storms as with a 31 foot boat I really did not want a confrontation with huge seas.

Pilots say “keep the blue side up” with sailing its the other way around. Your cat must be about 64 feet.

Here are some pic’s of pouch cells mounted in plastic frames, I have made compression frames with plywood and threaded rod as some posters on this forum have talked about....

The the iCharger you see in one pic does some of the functions of a BMS but it does not have cutoff capability , it is doing monitoring now but I can charge, discharge batteries with this device, sort of a testing setup....really meant for electric model aircrafters.....I started with very small packs of LiPo and LiLo batteries for experience.
Hey thanks for the great advice. So these QNBBM balances will work the same even if it’s 1P 4S or my new setup 3P 4S???

Yes, the Overkill solar instructions I read through also said hook up all wires first and only plug in the BMS at the end.

I’ll hook up all the cells first, testing as I go along. And then make all the connections last. Then finally plug in the BMSs at the end.

I’m doing charters by the cabin on my Lagoon 450F so you can most certainly join us. I needed someway to try and pay for the $100,000 refit. Ugh I’m going broke.
 

Tecnodave

Solar Addict
Joined
Mar 22, 2021
Messages
761
Hey thanks for the great advice. So these QNBBM balances will work the same even if it’s 1P 4S or my new setup 3P 4S???

Yes, the Overkill solar instructions I read through also said hook up all wires first and only plug in the BMS at the end.

I’ll hook up all the cells first, testing as I go along. And then make all the connections last. Then finally plug in the BMSs at the end.

I’m doing charters by the cabin on my Lagoon 450F so you can most certainly join us. I needed someway to try and pay for the $100,000 refit. Ugh I’m going broke.
These balancers will “see” the 3 cells as one cell so yes they will work in exactly the same manner. The only job that the balancers do is balance, but they do it better than the BMS can as they move more current actively whereas the BMS can only blow off of the excess charge of the “too high charged” cells as heat. The BMS also monitors for excess heat, excess high voltage, and too low voltage by shutting off that battery. Do be sure to get all the wires to the correct locations , check and double check, it just takes a fraction of a second to fry the delicate components of the BMS and balancers. Both devices do their job independently of each other. Do be sure to check the voltages on each pin of the connectors at each connector before plugging each connector to the BMS and the Balancer.

The one advantage of the Overkill package that you bought is the support that they provide. Very good instructions along with good support of the product.

You could have bought the same item from China but with zip squat nada support and documentation written by persons who speak and write pigeon english. So you made the right choice in buying good support along with a highly regarded BMS.

From what I have read the QMBBS balancers are the top of the line, but I did not want to put that much money in unproven cells so I opted for what I perceive as the “next best”

Please do note that all of my experience is with far smaller lithium battery packs, with only a small amount of power for portable applications. I have sucessfully repowered devices with lithium cells using no BMS on discharge but using a charger/balancer/discharger/tester to recharge. Absolutely no fails in about 5 years doing this. I have a fascination with model airplanes that can break 100 m.p.h. using only a small battery pack. That is where i started doing lithium.

The person whose knowledge of large scale LFP cells that i respect the most is on this forum as @Steve_S , you would do well to read some of his posts, he has a quite large set of lithium cells to run his homestead.

Would love to join you on a cruise in blue water but I am in California for medical care which I cannot find in Alaska, my home ground......Now that you have identified which cat that you cruise on I will look it up on the internet, My Trimaran was more of a backpackers rocketship on the water, Wicked fast with minimal accommodations, guess that i am a speed sailing junkie, had a Hobie cat, wicked fast...
 

Tecnodave

Solar Addict
Joined
Mar 22, 2021
Messages
761
The JBD have allready been ordered, paid for, delivered and at least partially installed. I have seen far too many Chinese suppliers weasel out of support, i just have no desire to deal with that. If there were LFP cells made in America I would have bought them. Tesla is local to me and as such I do have quite a few Tesla cells as used in their auto’s. I said cells, not packs.....right off the production line including 20700 cells

Most the gear in my solar system is “Made in America” high quality well supported gear meant to last.....MidNite, Exeltech, Trace, Morningstar, etc....My main battery is manufactured in Nova Scotia, By the best quality manufacturer.
I do have some offshore gear but made by well known well respected companies including Victron (Holland) and Samlex (Denmark)...etc....all these companies have great product, support, etc.

Every piece of Chinese equipment that I have purchased has had zip, squat, nada support or warranty as to the claims including but certainly not limited to EPneverreliable and Cotek to name a few

I will say that my Cotek inverter did give me 10 years which I consider exceptional but with Exeltech (21 1/2 years MTBF) why do i need less reliable.
 

TommyHolly

Solar Enthusiast
Joined
Jun 24, 2021
Messages
193
Gr
These balancers will “see” the 3 cells as one cell so yes they will work in exactly the same manner. The only job that the balancers do is balance, but they do it better than the BMS can as they move more current actively whereas the BMS can only blow off of the excess charge of the “too high charged” cells as heat. The BMS also monitors for excess heat, excess high voltage, and too low voltage by shutting off that battery. Do be sure to get all the wires to the correct locations , check and double check, it just takes a fraction of a second to fry the delicate components of the BMS and balancers. Both devices do their job independently of each other. Do be sure to check the voltages on each pin of the connectors at each connector before plugging each connector to the BMS and the Balancer.

The one advantage of the Overkill package that you bought is the support that they provide. Very good instructions along with good support of the product.

You could have bought the same item from China but with zip squat nada support and documentation written by persons who speak and write pigeon english. So you made the right choice in buying good support along with a highly regarded BMS.

From what I have read the QMBBS balancers are the top of the line, but I did not want to put that much money in unproven cells so I opted for what I perceive as the “next best”

Please do note that all of my experience is with far smaller lithium battery packs, with only a small amount of power for portable applications. I have sucessfully repowered devices with lithium cells using no BMS on discharge but using a charger/balancer/discharger/tester to recharge. Absolutely no fails in about 5 years doing this. I have a fascination with model airplanes that can break 100 m.p.h. using only a small battery pack. That is where i started doing lithium.

The person whose knowledge of large scale LFP cells that i respect the most is on this forum as @Steve_S , you would do well to read some of his posts, he has a quite large set of lithium cells to run his homestead.

Would love to join you on a cruise in blue water but I am in California for medical care which I cannot find in Alaska, my home ground......Now that you have identified which cat that you cruise on I will look it up on the internet, My Trimaran was more of a backpackers rocketship on the water, Wicked fast with minimal accommodations, guess that i am a speed sailing junkie, had a Hobie cat, wicked fast...
Great advice thanks!

Also, I have to say, I really have to give credit to DALY BMS company. They were extremely responsive, especially at night where it’s daytime in China. They would respond to me sometimes within minutes. Overkill Solar responds in 2-3 days at a minimum and one time it took them nearly 2 weeks!! So DALY has better customer service so far.

I have to figure out where I’m gonna sell that 500A DALY 4S LiFePo4 Smart BMS that I initially ordered. Or maybe I’ll use it on something in the future? Not sure what yet.
 

Tecnodave

Solar Addict
Joined
Mar 22, 2021
Messages
761
Based on what has been said about Overkill, I was going to purchase my JBD from them but they never responded and they were allways backordered. I had been hearing about current_connected so I ordered from, they had the units in stock, but very shortly got a call from them about their stock came with the wrong cable from China, They let me know right away, kept me informed, and shipped promptly, very well packaged. I still have not commissioned them as I am still building compression frames as I have very strange cells. So far so good...current_connected keeps you in the loop, to me very nessecary , I do not deal with vendors like Alibaba due to the very long response times for minor issues. I will deal with current_connected again.
 
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