Magical LiFePO4 batteries giving more than rated capacity!

[newbostonconst]

In parallel setups the voltage is going to be the same across all batteries (provided no bad connections, or shorted cells) Batteries are damaged when the voltage gets to high or to low but the Op's batteries have a BMS to protect against that. Resistance doesn't mater because they are all at the same voltage, if the voltage is the same they will all hit the knee in the curve the same and thus be nearly charged or discharged all together. If there is a weak battery and its voltage wants to drop it can't because it is tied to the others and they will supply the power.

Only situation that could be(but not likely) is in high power drain installs where the battery is drained in under an hour, but even in this situation there is a BMS in the OP's batteries.

How many parallel cells are in Tesla's?

 

[newbostonconst]

when talking very small resistances, even very nearly equal voltages like 0.001V could see 5A difference between parallel cells.

I = V / R = 0.001V/.0002Ω = 5A

you are applying a static solution to a dynamic problem.

 

[Ampster]

So far most of this discussion has been about parelleling batteries. Since most batteries internally consist of cells in series and parallel controlled by a BMS I am sure there is a limit whether it be best practices or manufacturers suggestion.

At the cell level I think the limit could be significantly larger. Certainly Tesla has successfully paralleled over 60 cylindrical cells. When one considers that some prismatics actually contain several pouches in parallel, then when we parallel those cells we actually have a lot more in parallel.

 

[sunshine_eggo]

Did you actually read the thread I linked?

In parallel setups the voltage is going to be the same across all batteries (provided no bad connections, or shorted cells)

Nope. Are very very slight voltage differences induced by the current and resistance. If what you say was true, then all batteries in parallel would always perfectly share the system current equally.

Batteries are damaged when the voltage gets to high or to low but the Op's batteries have a BMS to protect against that.

Batteries get damaged from operation. Identical batteries of identical ratings will experience different rates of wear at different utilizations, e.g., a 1C rated battery operating at 0.1C will last longer than a 1C rated battery operating at 0.5C.

Resistance doesn't mater because they are all at the same voltage,

Again, not true when you're looking at more decimal places.

if the voltage is the same they will all hit the knee in the curve the same and thus be nearly charged or discharged all together.

Are you aware that LFP in particular can have wildly varying SoC with almost identical voltages?

If there is a weak battery and its voltage wants to drop it can't because it is tied to the others and they will supply the power.

Right... the source of the imbalance I'm talking about.

Only situation that could be(but not likely) is in high power drain installs where the battery is drained in under an hour, but even in this situation there is a BMS in the OP's batteries.

It would be more of an issue in moderately utilized systems where low resistance batteries handle the brunt of the discharge requirement and subsequently receive the majority of the charge current.

How many parallel cells are in Tesla's?

Apples to oranges. Tesla only puts cells in parallel - not batteries. Tesla had to use off-the-shelf technology to succeed.

you are applying a static solution to a dynamic problem.

How do you figure? At any snapshot moment, it's mostly static, and the relationship holds.

 

[Archerite]

So far most of this discussion has been about parelleling batteries. Since most batteries internally consist of cells in series and parallel controlled by a BMS I am sure there is a limit whether it be best practices or manufacturers suggestion.

I never thought posting about my batteries giving more than their rated capacity would turn into an "argument" about paralleling batteries. if these were SLA batteries I would not have even thought of putting so many together. Even when I someday have those big blue LiFePO4 cells I would nu put single units in parallel...because I fear one cell might wear out more than the other and the BMS can't see it or correct it. I see people do it so maybe if they are perfectly matched in SoC and resistance that's ok...I don't know.

The biggest thing I miss about these batteries and their internal BMS is that it's not possible to have an app show the status of the cells. I have been looking in ready made batteries with bluetooth BMS's but they are expensive...and the cheapest ones don't have that much capacity. At least not for my requirements...which for the upgraded battery should have at least 150Ah at 12V! ?