Background

Minghao met with Prof. Michael Fowler in the Chemical Engineering department on the morning of Sept 20, 2017. Prof. Fowler was shown our compression-based proof-of-concept module assembly and asked for general input regarding pack design and verification. He also provided key contacts within the Chemical Engineering department for potential access to lab equipment and software.

Summary

Prof. Fowler sent the following email on Oct 9 summarizing his notes from our meeting:

Safety is critical.

1. Test each module first and then full pack testing.
2. The BMS should have extensive testing for all likely failure modes (a HIL – hardware in the loop testing should be OK)
3. The Pack Container must of able to withstand a Crash and/or Debris penetration. Solid state modeling and simulation is recommended.
4. Pack Container must fully isolate the driver from the pack.
5. Stefanie Bruinsma stefanie.bruinsma@uwaterloo.ca in GAIA may have a Pack Cycler you can test you pack on.
6. Compression electrical connections are not acceptable.  Everything must be welded or bolted.
7. Thermal modelling in COMSOL is highly recommended. Dr. Nasser Lashgarian Azadnlashgarianazad@uwaterloo.ca in Systems has done Air Cooling modelling for such packs.
8. Full Kapon Sheets are recommended between all modules and lining of your pack container.

Michael Fowler

E6 - 1110

519-888-4567 Ext 33415

mfowler@uwaterloo.ca

Pack Design

Compression vs. Spot Welding

Prof. Fowler was extremely opposed to our compression-based design, claiming that our contacts would be susceptible to arcing between cells and busbars, leading to poor pack performance and overheating. He strongly recommended spot-welding bus bars to cell terminals to guarantee robust contact in all operating conditions. He noted that we may be able to obtain a spot welder ourselves at a hobby shop but also gave a contact in the department with a spot welder (though he was not confident we would be able to access it).

Airflow

Prof. Fowler said that the gaps we have between every two cell rows for airflow are unnecessary and that the standard inter-cell gap provided by adjacent cell holders would be fine provided that we have active cooling. He initially proposed a stronger cooling solution such as a thermoelectric cooler but after Minghao explained that our motors have a combined draw of 20 hp, he became less concerned.

Regardless of our design, Prof. Fowler emphasized that it was critical for us to perform airflow and heat transfer simulations in COMSOL (or ANSYS). He said that all chemical engineering students have access to COMSOL through servers but that he could also help us obtain access as a team. COMSOL is supposed to have Li-ion models built-in.

Materials

Prof. Fowler warned us against using acrylic (plexiglass) in the battery since acrylic is flammable and adds weight. For electrical insulation of exposed conductors, he suggested Kapton (this could not be confirmed because he could not recall the name, so Kapton is Minghao's best guess as to what he was referring to).

He also inquired about plastic conduits covering 2 gauge wires. He suggested to see UWAFT's battery pack for this.

He emphasized in the strongest terms that our pack needs to protect against penetration of foreign objects and debris, as well as be designed for crash-safety. He suggested at the minimum to use Kevlar in the enclosure.

Contacts

Prof. Fowler provided a number of contacts within the department. They are listed below:

Stefanie Bruinsma - Powertrain Research Technologist in GAIA - Access to battery tester for cycling modules and the pack

Zongwei Chen - Canada Research Chair, CHE - Possible access to spot welder

Nasser Azad - Associate Professor, SYDE - Has had some students do thermal modelling for air-cooled battery packs in the Toyota Prius

Dana Incorporated - Company that makes battery cooling and other systems for EVs