Charging to 100%, voltages, soc, and capacity

[Firn]

Recently charged from 50%to 100% and threw car scanner on it while I did so. Here are the results.


SOC, SOC displayed, and capacity.

Module voltage

Average module voltage at 100% soc displayed was 4.09v. Considering a 3.0v to 4.2v range for NMC that translates to 90% peak for the chemistry.

Previous charges indicate a module voltage of 4.04v at 90% displayed soc.

So there is some top buffer, but not a huge amount.

 

[Maquis]

I don’t understand how the kWh can drop while charging? Red curve.

 

[Firn]

I don’t understand how the kWh can drop while charging? Red curve.

I'm not sure either. It happens at the same time that the truck reached "100%" so I'm assuming it is related to the charger turning off. I'll pull the voltages here when I can.

 

[Firn]

There was around a 1v drop in pack voltage at the time the charger stopped, this is also the exact time the capacity dropped.

Looking quickly at the data and it appears 1v change in pack voltage while charging does corelate to that amount of energy.

 

[Effonefiddy Lightning]

Me, clueless as to what these graphs even mean.

 

[Jim Lewis]

IIRC, the total real capacity of an ER battery is 143 kWh, with some buffer at the top and bottom of the real range. Your avatar shows a snowy environment. There are not too many trees on the North Slope, but maybe the temperature of your charging experiments is an important parameter to keep track of, especially in comparing similar experiments done at different times of year, different truck mileages, etc.

 

[Firn]

IIRC, the total real capacity of an ER battery is 143 kWh, with some buffer at the top and bottom of the real range. Your avatar shows a snowy environment. There are not too many trees on the North Slope, but maybe the temperature of your charging experiments is an important parameter to keep track of, especially in comparing similar experiments done at different times of year, different truck mileages, etc.

The "top buffer" was ultimately my reason for doing this. That top buffer is nothing more than limiting the maximum voltage.

Pack voltage was 392v with a cell voltage of 4.09v at 100% displayed SOC. Assuming a 3.0v minimum voltage, and running the cells out to 4.2v per cell, would give you and overall capacity of ~139kwh, or very close to the label capacity.

 

[Maquis]

There was around a 1v drop in pack voltage at the time the charger stopped, this is also the exact time the capacity dropped.

Looking quickly at the data and it appears 1v change in pack voltage while charging does corelate to that amount of energy.

The drop in voltage is likely causing the energy graph to drop, but only because the algorithm to determine SoC uses pack voltage. In reality, the stored energy did not go down.

 

[chl]

Why does battery voltage drop after charging?

This is often the normal behavior of the cell. A cell's voltage will rise when it is being charged and will begin to drop somewhat after the charge current has been removed. This is a result of many factors, but primarily due to internal resistance of the cell and the charge characteristics of the chemistry.

https://www.orionbms.com/troubleshooting/cell-voltages-drop-charge-completes/

So the drop does appear to be when the charger turned off.

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