BMS on parallel battery pack

[Gagile]

Hello,

I'm totally beginner in this area, and this question was probably already on forum. Sorry for asking again.

On my boat I use 4 12 V batteries connected in parallel. I planing to swap them for some now ones and thinking to upgrade system with some kind of BMS.
I found that BMS on parallel system is not possible, but I'm asking again, but please with simple answer thus I'm a newbie :D
Every video on net is presenting with serial connection.
- So does it possible and make sense?
- Second question, if I want to add some more batteries in the future. Can I buy BMS for, let's say, 8 batteries and for now connect it only on 4 for now? Does make some impact in that case?
- If BMS is not possible in parallel, is it OK to use BMS that are already build in batteries?

Thanks in advance

 

[SolarPrep]

Gagile:

First, lead acid, or lithium for your boat? If lithium, you should have a BMS.
Second, you can put a BMS on batteries in parallel. The BMS will have to be tailored to how many cells you have.
Third: Series connection is to increase voltage. IE (4) 12v in series is 48 volt.
Fourth: your example of 8 batteries, or 4 batteries can only be answered if we know what chemistry, and what type of cells. When you say "battery", do you mean a finished battery, a single cell, etc. If you are referring, for example, to an 8s BMS, that is referring to how many cells or units are placed in series. Or, 8s4p would mean 8 in series, 4 in parallel.

Adding batteries in parallel increases the size of the battery capacity, not voltage. Like a "bigger gas tank".

Keep reading and asking questions!

 

[Gagile]

Thank for fast reply.

My old batteries are lead ones, and now I'm aiming for lithium.
Yes I know that in parallel only capacity increases, and that is my goal, to stay on 12 V with larger capacity.
When I say batteries, I mean a finished one.
BMS 8S for example, I mean the one with 8 red cables and one black :D

My current situation is on first picture. Only two batteries inside over the winter for bilge pump. Six, and a starter battery is out.
Goal is almost like on second picture, but only one fuse, and adding BMS.

And please if you can draw me a example how to connect the system.
Again thanks.

 

[Texas-Mark]

If you are going are stay at 12V, you will need either a BMS for each set of 4 cells. or a BMS with a high enough current rating to parallel the cells that are than put in series. Either way you would need one or more 12v4S BMS