Parallel connection

[Solarguy]

Hi,
Sorry if the question has been answered already.

I have two lifepo4 batteries 200Ah each and 48V.
Let's call them battery A and B

A has 200A daly bms and the other one has B=100A daly bms. Battery A has around 300 cycles completed and B has almost 180.

Question is: can I connect these two in parallel without any communication between them. Plain + to + and - to - connection.

I actually had both connected and problem is battery B discharges sooner than battery A. The discharge currents are different. Both gives me ~10kwh if discharges separately hence both are healthy. I disconnected them because i feared one going under minimum volt.


Thanks

 

[sunshine_eggo]

Hi,
Sorry if the question has been answered already.

I have two lifepo4 batteries 200Ah each and 48V.
Let's call them battery A and B

A has 200A daly bms and the other one has B=100A daly bms. Battery A has around 300 cycles completed and B has almost 180.

Question is: can I connect these two in parallel without any communication between them. Plain + to + and - to - connection.

I actually had both connected and problem is battery B discharges sooner than battery A. The discharge currents are different. Both gives me ~10kwh if discharges separately hence both are healthy. I disconnected them because i feared one going under minimum volt.


Thanks

Yes.

link #6 in my signature for bes practices.

 

[Mattb4]

With 1 having a 100A BMS you will be limited to ~ 200A discharge. If both had 200A BMS's you could reach 400A. This is approximate values since each battery will be slightly different in how much load is picked up.

 

[Solar Guppy]

Yes and it adds redundancy if one goes offline the system doesn't go dark

 

[Solarod]

Hi,
Sorry if the question has been answered already.

I have two lifepo4 batteries 200Ah each and 48V.
Let's call them battery A and B

A has 200A daly bms and the other one has B=100A daly bms. Battery A has around 300 cycles completed and B has almost 180.

Question is: can I connect these two in parallel without any communication between them. Plain + to + and - to - connection.

I actually had both connected and problem is battery B discharges sooner than battery A. The discharge currents are different. Both gives me ~10kwh if discharges separately hence both are healthy. I disconnected them because i feared one going under minimum volt.


Thanks

The important question is: how is the load connected to the parallel connected batteries?

 

[Solarguy]

The important question is: how is the load connected to the parallel connected batteries?

Inverter @deye 6kw is connected to the combined output of both batteries.

 

[Solarguy]

Yes and it adds redundancy if one goes offline the system doesn't go dark

What is your opinion on one battery discharging sooner than the other? Amps are unequal during discharge

 

[ricardocello]

What is your opinion on one battery discharging sooner than the other? Amps are unequal during discharge

Consider changing the total lengths of the battery cables so they have equal current discharge.

 

[Solarod]

Inverter @deye 6kw is connected to the combined output of both batteries.

You are apparently not using the diagonal connection like this:


Also see: https://diysolarforum.com/threads/no-busbars-needed-with-two-batteries.66691/

 

[Solarguy]

You are apparently not using the diagonal connection like this:
View attachment 261925

Also see: https://diysolarforum.com/threads/no-busbars-needed-with-two-batteries.66691/

No, i have connected the main cables on the same side. also tried connecting the main cables on the other side but same results.

Sorry for the delayed response.

 

[hwy17]

You don't have to worry about uneven discharge, because of Lifepo4's voltage curve the other one will always catch up at the bottom or top. In parallel it can't pull one battery to low voltage without the other one unless the cables are too small.

I have a 5kWh and 15kWh wired in parallel with totally uneven connections and I just don't pay attention to the 5kWh. They will often report different SOC but you still get full capacity out of both by the time you get to 0 or 100.

 

[LakeHouse]

They will often report different SOC

And likely they are almost always actually at different SoC. But I 100% agree that there's no reason to worry about that.
Too many people on this forum spend far too much time and energy worrying about their LFP batteries not charging and discharging exactly the same. In most cases it just doesn't matter.

 

[Solarod]

No, i have connected the main cables on the same side. also tried connecting the main cables on the other side but same results.

Sorry for the delayed response.

You need to connect one of the main cables to one side and the other main cable to the other side.. This is the diagonal connection like the image in post #9.