Ni-MH Open Circuit Voltage vs State of Charge
Can we tell the state of charge of NiMH cell by measuring its open circuit voltage?
According to papers I read on internet it is possible. So let’s put it into test.
Test object: Panasonic Eneloop for its
consistency and low self-discharge
Currents: 1.0A charge current, 0.5A discharge current
Test steps: for different state of charge repeat:
- discharge the cell to 0.9V
- charge a certain amount of mAh into the cell (in 100mAh increments)
- measure the voltage of the cell after it rested 24 hours
- plot the measured data into graph
Voc as a function of SoC
** !!! DRAFT - THIS IS STILL A WORK IN PROGRESS !!! **
SoC as a function of Voc
By swapping X and Y we get the inverse function - useful for estimating the state of charge from open circuit voltage.