Smart Measurement Solutions Bode 100 - Application Note Battery Impedance Measurement 深圳市迪福伦斯科技有限公司w w w . d e f f e n s e . c o m . c nBode 100 - Application Note Battery Impedance Measurement Page 2 of 9 Smart Measurement Solutions Smart Measurement Solutions Table of Contents 1 Executive Summary . 3 2 Measurement Task . 3 3 Measurement Setup & Results . 4 3.1 Device Setup . 5 3.2 Calibration . 6 3.3 Measurement . 7 4 Conclusion . 8 Bode 100 - Application Note Battery Impedance Measurement Page 3 of 9 Smart Measurement Solutions Smart Measurement Solutions 1 Executive Summary Battery impedance includes information about the internal state of a battery. The impedance depends on many factors such as the chemical properties and mechanical design of the battery. Measuring the battery impedance over frequency helps to identify the characteristics of the battery. The Bode 100 in conjunction with the Picotest J2111A Current Injector offers an easy way to measure the impedance of a battery in the frequency range from 1 Hz to 10 MHz. This application note shows the connection setup and the device settings of the Bode 100 necessary to perform the impedance measurement. 2 Measurement Task The impedance of an alkaline 9V block is measured in the frequency range from 1 Hz to 10 MHz. After discharging the battery to a no load voltage of 0= 7.5 V the impedance spectrum is measured again and compared to the measurement performed on the full charged battery. Furthermore, the impedance spectrum of a 3.7 V lithium ion battery is measured to demonstrate that even cells with low output resistance can be measured with the presented method. Bode 100 - Application Note Battery Impedance Measurement Page 4 of 9 Smart Measurement Solutions Smart Measurement Solutions 3 Measurement Setup & Results The impedance of a battery, , can be measured by loading the battery with an AC1 current and measuring the resulting AC output voltage of the battery. Dividing the AC output voltage by the AC output current leads to the impedance of the battery. = The output current of the battery is modulated by the J2111A current injector, driven by the output signal of the Bode 100. The output current is then measured by connecting CH1 of the Bode 100 to the current monitor output of the J2111A. The output voltage of the battery is measured directly using a 1:1 voltage probe connected to CH2. The connection setup is shown in the figure below: Figure 1: Connection Setup Note: The maximum allowed battery voltage with this setup is 40 VDC ! 1 Alternating Current (sine-waveform) Bode 100 - Application Note Battery Impedance Measurement Page 5 of 9 Smart Measurement Solutions Smart Measurement Solutions 3.1 Device Setup Current Injector J2111A: The positive bias of the Current Injector must be switched on (+bias) since the Bode 100 output voltage does not have an offset. The positive bias provides a 25 mA offset current, allowing the current injector to operate in class “A” mode. For the best performance, the output wires from the J2111A should be twisted or be coaxial. Bode 100: The battery impedance measurement can be performed directly with the Bode 100 using the external reference function. The Bode 100 is set up as follows: Measurement Mode: Frequency Sweep Mode Start Frequency: 1 Hz Stop Frequency: 10 MHz Sweep Mode: Logarithmic Number of Points: 201 or more Receiver Bandwidth: 100 Hz Attenuator 1 &2: 0 dB Level: 0 dBm To switch on the external reference start the device configuration window and click on the external reference switch symbol: In addition, the input impedance of channel 1 must be set to 50, while channel 2 need to remain in high impedance mode: Bode 100 - Application Note Battery Impedance Measurement Page 6 of 9 Smart Measurement Solutions Smart Measurement Solutions Trace 1 settings: It is advisable to activate the Full Speed Mode to achieve a higher measurement speed since we are measuring over a low frequency range. 3.2 Calibration To remove the influence of the voltage probe, we recommended calibrating the setup. To do this the voltage probe at CH2 is connected to the curre