Learning Forum

[Evan Sandoval]

I'm currently interested in using Ansys Fluent to model the heat dissipation of a Lithium Ion Battery. I've been referencing the Fluent manual for development, however I am curious about the input data for the ECM parameter estimation tool. The following is an excerpt from the Fluent manual 30.2.3.4.4. I have a couple of questions about the data collection:

My questions are as follows: 

• Does the pulse current need to be constant throughout the discharge? Our team was thinking about applying a load through the resistor to get a measurable current, however it would change throughout discharge as the voltage of the battery drops. Is it critical that we use an e-load for a constant current, or is an approximately measured current with the resistor sufficient?
• How long do we have to pulse the battery for? My interpretation of the manual is that pulse length is not important as long as the voltage data contains data from the rest, pulse, and relaxation period.
• Is SOC measured absolutely from the battery, or arbitrarily as determined by our operating range? For example, batteries are rated to be in the range of 2.8V to 4.2V, but we want to keep them in the range of 3.0V - 4.0V. So would a voltage of 3.0 correspond to a 0 SOC (as calculated in our range) or a 0.14 SOC (as calculated in the battery's range)?

Any help would be appreciated, thank you!

[Murari Iyengar]

Hi Evan,

Testing is done by many sources who use different methods to get the voltage curves. The recommended method in the User Manual is the best method for ECM parameter estimation but you are free to do use your own procedures. So to answer your questions, 1. Approx current with a resistor is sufficient. 2. Pulse should be long enough for the battery to reach steady state/not have any fluctuations. That being said there is no 1 specific pulse length as it depends on various factors such as cell material, age, etc. 3. SOC can be determinded by your operating range as the testing data is used mainly for parameter identification.