Large Single Battery vs Smaller Ones- Resurrecting this old topic

[toms]

What happens if you directly parallel that up other healthy cells I have no idea, but the results can never be good.

I guess it’s just the vibe of it then.

In parallel the cells are voltage locked. In your instance the accompanying parallel cells would also have been discharged to zero at the same rate.

Describe to me how extra capacity at the same voltage can decrease the resistance inside a cell.

 

[toms]

If you are saying that it's impossible for a LiFePo4 cell to develop a dead short, that's wonderful news.
Otherwise, I would recommend protecting against what could be a very bad day.

No. I’m saying that a short circuit in a single LiFePO4 will have the same outcome as a short circuit in a parallel pair of cells.

What is it that you are doing with your battery to prevent a disastrous outcome from a short circuit in one of your cells (or should i call the fire brigade and ask them)

 

[Warpspeed]

No not the same outcome.
If only one cell fails shorted, that is unfortunate.
With a whole bunch in parallel, you lose all of them.
The difference is in the cost of replacement.

I have wondered what would happen if when initially top balancing new cells at maximum voltage, with all cells connected in parallel, and one decides to short out.

 

[timselectric]

I give up. Good luck to you.

 

[toms]

I give up. Good luck to you.

Which part have you given up on? Your inability to explain what happens when a LiFePO4 cell has an internal short?

Keep spreading unsubstantiated and incorrect information like parallel cells needing intercell fusing if you like,

If you really can’t see there is no difference between a short circuit internally in a 200ah cell, and a short circuit internally in a 100ah cell that is in parallel with another 100ah cell i’m afraid i can’t help you further.

 

[toms]

No not the same outcome.
If only one cell fails shorted, that is unfortunate.
With a whole bunch in parallel, you lose all of them.
The difference is in the cost of replacement.

I have wondered what would happen if when initially top balancing new cells at maximum voltage, with all cells connected in parallel, and one decides to short out.

I agree you may well lose all cells that are in parallel. That is a far cry from the alarmist view that you will be asking the fire brigade why your house burnt down.

Over the last decade i have installed over 1000cells in parallel applications, i have had several cells fail within a cell parallel pair without destroying their partner. I’ve not seen a failure of the type you describe.

In the case of parallel cells / parallel batteries, the upfront saving on BMS can be used as insurance against an extra cell replacement.