Getting started with battery profiling

Otii hardware with battery validation setup

1. Connect the battery to Otii Arc main terminals, red to positive pole of battery and black to negative pole.

2. Find stated battery capacity in the datasheet

3. Decide how long time the profiling should take, this decides the average discharged current EQUATION Note: Coin cell batteries must never be profiled for a shorter time than one month (roughly 720h).

4. Profile setting currhigh should be set to, or slightly above, your systems peak current for coin cell and lithium thionyl chloride batteries. For alkaline batteries it could be set slightly higher and for lithium secondary cells, it could be set much higher, but check battery datasheet for information about recommended maximum discharge current.

5. Profile setting currlow should be set with as big difference as possible from currhigh since the battery profile resolution depends on the difference between currhigh and currlow EQUATION Note: Currlow should not be set to too low value so the battery needs to be “restarted” again, there are chemical effects in the battery that should be avoided. Check with the battery manufacturer regarding this. However, usually this value is higher to get a decent duty cycle between high and low current consumption.

6. Cycle time of the profiling should be set so number of iterations is reasonable (higher number of iterations might be needed for long profiling times, like for profiling coin cell batteries but the battery profile will also then be larger). EQUATION Note: A cycle time of 30s to 180s is usually a good choice.

7. Calculate timehigh and timelow by cycle time and average discharge current EQUATION

8. Check battery datasheet for when the battery is considered discharged, this gives min_ocv_voltage (V)

9. Check battery for nominal voltage, this gives start_voltage (V)

10. If you experience that you get voltage drop in your cables when discharging then you can set fourwire = true and connect sense+ and sense– to the battery, otherwise you set it to false. Usually this is set to false except for secondary cell lithium batteries.

11. Enter the settings above in the battery profiling window and add information about the battery.

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Battery Profiles on GitHub

Otii Battery Toolbox comes with a number of already profiled, real life batteries. You can find these in the drop down meny under the Supply in Project Settings. Here is also where you can find your own profiles, once created.

There is also Qoitech Github with more battery profiles available.