2P4S and 4P4S 12v lithium

[ken_lillia]

Good morning from sunny Queensland Australia. Giving som thought to prismatic cells and issues that could arise in a 4S 12v battery if one cell dies. If I build say for instance a 4P4S 200ah battery using 50ah prismatic cells and one of the cells becomes faulty and dies.
1) would the battery still work @ 12 volts?
2) The ah would drop by how much
3) would it damage the other cells?
The reason I ask is that if you have a cylindrical cell collapse the whole battery continues to operate at a reduced capacity.
therefore a prismatic cell setup would do the same in a 4P4S set up. ???

 

[Ampster]

The result would be the same whether the cell is round or rectangular. There is no difference in the physics. Removing 1/4 of the capacity of parallel cells would reduce the capacity of the pack by 1/4 but the voltage would be the same. However the cylindrical cell that you are referencing may have some sort of fuse that would electrically remove it from the rest of the pack. If a cell goes bad in a pack and it does not have a fuse a lot of different things could theoretically happen, some of which might not be good. Most cells go bad slowly over time but that is no guarantee.
The question is hypthetical but I had to make assumptions to answer it and the answer is only as good as the assumptions. Your facts or assumptions may be different so this is no guarantee that it will work in your situation.

 

[ken_lillia]

Reason for question is if I am camping or boondocking in the outback and one cell goes bad I can still have power.

 

[Ampster]

I understand. I remember before batteries were light weight worrying about my matches getting wet.

 

[ken_lillia]

Exactly, it was just a thought.
thanks for you reply, and your humour.

 

[tictag]

To be honest, assuming you have a BMS, as soon as a cell indicates that it is damaged, the entire battery will be disconnected / fail. There are no good or even acceptable outcomes resulting from single cell failure. One cell dies, battery dies.

...but it is very unlikely to happen with matched, similar batch/manufacturer, undamaged cells!!

 

[schmism]

Reason for question is if I am camping or boondocking in the outback and one cell goes bad I can still have power.

As tictag said, its all or nothing. But that doesnt limit you to reconfigure the pack and remove the 4S that has a bad cell still giveing you battery power albeit half as much.

 

[ken_lillia]

To be honest, assuming you have a BMS, as soon as a cell indicates that it is damaged, the entire battery will be disconnected / fail. There are no good or even acceptable outcomes resulting from single cell failure. One cell dies, battery dies.

...but it is very unlikely to happen with matched, similar batch/manufacturer, undamaged cells!!

 

[ken_lillia]

Thanks for your input. I have learnt something new.

 

[Ampster]

As tictag said, its all or nothing. But that doesnt limit you to reconfigure the pack and remove the 4S that has a bad cell still giveing you battery power albeit half as much.

My emergency kit when I was young and went camping often included string, some duct tape and of course some matches in a waterproof enclosure. Today if I had a 4P battery pack in my pack I would include a bit of wire and with my trusty Swiss Army knife or Leatherman tool I could rig a jumper to bypass the dead cell and get my battery working again.

 

[seamad]

Good morning from a fellow sunny Queenslander.
My camper only has 4 cells, but my sailing cat has 2p4s. With the latter, would it be OK with a single cell failure to just remove the faulty cell ?
That is use the 7 cells with 3 X 2p and a single ?
Or is it better to just revert to a 4s ?
This would only be a temporary measure .

 

[Ampster]

would it be OK with a single cell failure to just remove the faulty cell ?
That is use the 7 cells with 3 X 2p and a single ?
Or is it better to just revert to a 4s ?
This would only be a temporary measure

You would need to keep and eye on the single cell because it will discharge twice as fast as the others, At the point that it hits bottom you would need to revert to 4S to limp home. Hopefully when that happens the wind is at your back.

 

[ken_lillia]

Still learning , I need to draw up to 2000watts for microwave in RV. I have 200ah lifepo4 12 volt battery, prismatic cells. What size BMS should I use.

 

[Ampster]

2000 Watts at 12 volts is 167 Amps. Will recommends some headroom so 200 to 250 Amp BMS.

 

[ken_lillia]

Any brand recommendations?