Two 8S LifePo4, want to parallel them

[Sipneat]

Hi All!

I have two (2) 24V battery packs made up of 8s TopBand 25ah batteries. Each one has a BMS (temp, etc). I would like to create a 8s2p but as a n00b have some concerns. Can I just parallel the two packs, leave the BMS's separate and off I go, or is there more to it? I know I could do a 16s or a 8s2p, its the two BMS's that have me wondering if and how to connect those. They are going to be connected to a MPPT controller. Thanks for any feedback, just trying to sort out how to use all the batteries as efficient as possible!

Thanks!

 

[rmaddy]

If the BMS supports being put in parallel you can just connect the two batteries in parallel. The battery manufacturer should state whether the batteries can be put in parallel or not. Most do but you should verify.

16S is not an option. That would be for creating a 48V battery.

 

[Sipneat]

OMG, well I just found that FilterGuy has the EXACT diagram Im looking for... that was easy (and yes I kinda feel like an idiot, search first!)

 

[Sipneat]

If the BMS supports being put in parallel you can just connect the two batteries in parallel. The battery manufacturer should state whether the batteries can be put in parallel or not. Most do but you should verify.

16S is not an option. That would be for creating a 48V battery.

Thank you! My understanding is that they can... and having a 48V would be OK but I was wondering about how to go about that wiring wise but looks like its just the combination of the mains from the battery packs and the BMS's...

 

[rmaddy]

You said you want the 2 24V batteries in parallel. That would still be 24V.

If you actually want a 48V battery then you need to wire the 2 24V batteries in series. Big difference. And not all BMSes can be wired in series.

 

[DLTooley]

There are possible issues with two batteries on a single controller.

The issue I’m aware of is that both batteries need to be relatively similar in capacity, age etc. Matched and balanced, if you will. This would apply to both a series and parallel connection between the two batteries. This may be less of an issue with LFP.

 

[jpimlott]

There are possible issues with two batteries on a single controller.

The issue I’m aware of is that both batteries need to be relatively similar in capacity, age etc. Matched and balanced, if you will. This would apply to both a series and parallel connection between the two batteries. This may be less of an issue with LFP.

This not an issue for LiPo4 at all.
You can run any combo. I have a 180 amp hr and 2 280 amp hr batteries connected in parallel for years and they work great.
Aging is not a problem with lipo4 is they just discharge quicker reach low voltage shutoff before the other ones.
At very high loads one bms could reach its limit before others do then all the batteries will shutdown.

 

[jtvt]

Works, but you have to address the following: If one bms offlines a string, does the controller exceed the other string's max charging amp? Does it exceed the amperage capacity of the wire? Same situation on the discharge side. Other problems can happen depending on use case. For example, if you are powering an inverter and a single string doesn't have the AH to support the inverter.

 

[jpimlott]

I have tested when the total load is too high the available power.
It shuts down completely.
Charging should not be an issue. Typical BMS can handle 100 up and down.
So charging should not be a problem unless you are pushing it.
On discharge then the loads can overwhelm one battery and it shuts off too.
I did this testing and it is like any other overload condition. the BMS protects itself.
The wire should never be overload the BMS should disconnect first or the wire is too small.