Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Paralleling Battery Packs
#1
I have a couple 15s17p li-ion packs. Each one was once rated for just over 2kwh of storage. I was going to put a 15s smart bms in each pack and then parallel the output from the BMS to support a larger load. Then I came across these boards: https://www.amazon.com/Amass-Parallel-Ch...B075CBGX5K
Obviously that isn't for a 15s pack but would something like that work for connecting more than one 15s pack together? If I understand correctly the + and - are paralleled like normal. The difference is that all the balance leads are also paralleled. I don't quite get that how that would work, if it would in fact work.
Reply
#2
Potentially yes. Above is not high enough though
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
Reply
#3
Yes, it could work. All this would do is make it so that all the outputs of the packs are paralleled together, which you were doing anyways, but it would also connect each of the smaller paralleled cells in parallel as well so you only need 1 bms.
The biggest issue with this is that you need to make sure that "all" groups of cells are at the same voltage "before" connecting them to the balance board. Otherwise, you could melt the small wires used for the balance leads.
So not only do both packs need to be the same voltage, but every parallel section of cells need to be the same as well, at least with it's twin in the other pack.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#4
(08-05-2019, 06:05 AM)daromer Wrote: Potentially yes. Above is not high enough though
I do realize the s count isn't high enough. That board just got me thinking about it.


(08-05-2019, 12:03 PM)Korishan Wrote: Yes, it could work. All this would do is make it so that all the outputs of the packs are paralleled together, which you were doing anyways, but it would also connect each of the smaller paralleled cells in parallel as well so you only need 1 bms.
The biggest issue with this is that you need to make sure that "all" groups of cells are at the same voltage "before" connecting them to the balance board. Otherwise, you could melt the small wires used for the balance leads.
So not only do both packs need to be the same voltage, but every parallel section of cells need to be the same as well, at least with it's twin in the other pack.

Thinking about strategy here... I could fully charge a pack and make sure it was balanced and then fully charge the next pack and make sure it was balanced and then connect the two in parallel on both the power and the balance leads.

Thanks for the help. This didn't quite make sense to me but if the experts think it is okay then I'll go with it!
Reply
#5
If parallel2 batteries that delivery 10a@12v each I can get 20a@12v out it.    
IF I join the balance leads like this:

And if the balance leads are 'thin'  (e.g. can only handle 10a).   Don't I run the risk of 20a going thru them...  and melting them thru?

My question is - how does current flow thru the main wires vs balance wires when you parallelize a couple of batteries as shown in this drawing.
Reply
#6
They flow to Keep balance.

Here have i done it

https://youtu.be/sGj9UrfEcAw
OffGridInTheCity likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
Reply
#7
(08-05-2019, 06:42 PM)OffGridInTheCity Wrote: My question is - how does current flow thru the main wires vs balance wires when you parallelize a couple of batteries as shown in this drawing.

Current on the string level will primarily run through all the packs to the end, it won't go from one string to the other through the balance leads. And if it does, it's negligible. Or there's a bigger problem; like one of the packs is not as strong as the other packs and is pulling the whole system down.
OffGridInTheCity likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#8
I find that often when people want to build packs everyone tells them to build them as parallel groups and then put those groups in series and note them such as 7s10p.

Along the same lines as my original question is this: if I built ten 7s1p pack and then paralleled all the packs I would have the same amount of power as I mentioned on the line above. The difference is that I would need 10 7s BMS units to control each pack. Why wouldn't I just make a jumper board that allows 10 of the 7s balance plugs to parallel into the board with one output to the bms. Then I would have a more modular pack (I could take a 7s1p pack out of service and keep my main voltage just with 10% less pack capacity) and still only require one BMS.
Reply
#9
(08-05-2019, 08:45 PM)gpn Wrote: I find that often when people want to build packs everyone tells them to build them as parallel groups and then put those groups in series and note them such as 7s10p.

Along the same lines as my original question is this: if I built ten 7s1p pack and then paralleled all the packs I would have the same amount of power as I mentioned on the line above. The difference is that I would need 10 7s BMS units to control each pack. Why wouldn't I just make a jumper board that allows 10 of the 7s balance plugs to parallel into the board with one output to the bms. Then I would have a more modular pack (I could take a 7s1p pack out of service and keep my main voltage just with 10% less pack capacity) and still only require one BMS.

There is nothing wrong with this, and that is exactly what OffGridInTheCity put in his diagram. We aren't saying this is wrong.

And there are several builders on SLS that have done just this, just with different packs in series, and with different count of cells in parallel in each group.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#10
@daromer - yes I have indeed watched that youtube on parallizing balance leads with great interest and it makes sense.
@Korishan - thank you for your comments about current flow - it makes sense.
Both of you - I haven't tried the balance lead parallelization as I was unsure about current flow but I do understand what you both are saying in this thread plus I have confidence in your expertise and can put it to rest in my mind. I may very well use this technique as I continue building battery packs.
Korishan likes this post
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)