Open Circuit Voltage Demystified

Open Circuit Voltage (OCV) is a key measurement for Li-Ion battery cells. It can be used to create a battery equivalent model, to design a Battery Management System (BMS) or to simply evaluate battery specs and condition.

OCV is generally not just “a” measurement, but a set of measurements. In fact we call it the “OCV characterization of the battery”, and we trace an exhaustive analysis derived from a curve on a State-of-Charge (SoC) versus OCV plane.

To trace this curve, you need to bring the battery to specific states of charge, typically by charging or discharging current in a pulsed way, then wait for some settlement time (called “relaxation”), and then measure the open-circuit potential at the electrodes.

A Keithley SMU like the 2461 is a perfect solution to perform this test. In fact it can either source or sink the cell current in a controlled way while measuring the cell current and voltage with a 4-wire (Kelvin) connection with contact check.

All this easily automated and controlled by a programmed embedded microprocessor.

Check out more here on SMU2461 > https://uk.tek.com/datasheet/2461-graphical-source-measure-unit

But what about the accuracy of the voltage measurement?

In some cases, the 6 ? digits measurement resolution, the thermal stability but mostly the accuracy of a SMU can be considered not sufficient.

For this reason some test setups involve a special digital multimeter, the DMM7510, that became a standard in Li-Ion battery cell testing.

Its low noise 32 bits A-D converter allow 7 ? digit resolution and metrology grade accuracy.

Check out for your specs needs and remember that we can combine this DMM7510 with a programmable precision DC source in order to let you work in the operating range better fitting your spec needs for resolution, accuracy and temperature coefficient.

Check out more here on DMM7510 > https://uk.tek.com/tektronix-and-keithley-digital-multimeter/dmm7510