Sponsor: Marc Johnson

Mentor(s):

Marc Johnson johnson.pmarc@yahoo.com

Michael Harmon

Project Background and Need:

Hybrid vehicles depend upon a large, high-voltage battery and an electric motor/generator to augment an internal combustion engine. The high-voltage battery has a limited life, and typically begins having problems after 8-12 years, 150,000 to 200,000 miles, and/or after long periods of not being used. Common failure mechanisms include reversed/shorted battery cells, as well as the capacities of functional cells becoming unbalanced.

Failing hybrid batteries may often be reconditioned. The process consists of breaking down a hybrid battery pack into its constituent battery modules. The battery modules are then individually tested so that good and bad modules may be identified. As part of this process, the cells in the good modules are balanced and the capacities of the good modules are assessed. Reconditioned battery backs are then assembled using the good modules.

The process of testing and balancing a battery module consists of repeatedly charging and discharging it. A fundamental issue with any battery charger is determining when to stop the charging task. A premature cessation of a charging task leaves the battery without a full charge, which defeats the intended balancing of the cells. Conversely, ceasing the charge well after the battery is fully charged leads to the battery becoming overheated, which may degrade the battery due to electrolyte loss or related.

Triggers for stopping the charging of a battery typically rely upon battery voltage, battery temperature, or some combination thereof. This project requires development of an apparatus to measure the temperature of Prius NiMH battery modules while they are being charged and discharged. The apparatus must require no physical contact, must be capable of measuring an array of battery cells simultaneously, and must have a simple/minimal interface for a microcontroller to read the temperature measurements.

Problem Description/requirements (List of high-level functionality you expect to see in the end product):

• Design/build a device for measuring battery temperature during charge and discharge cycles.

• Each battery cell within a 6-cell battery module should be monitored.

• Temperatures for multiple battery modules must be monitored in parallel.

• Temperature sensing should be contactless.

• Temperature measurements shall be digitized and provided to a microcontroller or PC over a single serial interface.

• Cost: <= $200 for a device that measures 6 cells for each of 40 modules

Required Skills / Desired Competencies (in order of importance):

• Analog and digital hardware design

• Embedded hardware and software serial interfacing (I2C, SPI)

• 3D printing and/or familiarity with basic mechanical fabrication techniques

• Basic PCB design

• Battery familiarity

How often and how would you be available to meet/chat with the team (Zoom, Hangout, Skype, Phone)?

Team members need to visit Green Bean Battery’s facility in Pittsboro occasionally, e.g., 2-3 times per semester, in addition to regular meetings.

Will the students be required to sign any of the following before they start with the project? NDA / CDA / IP assignment / IP protection form

Team members will be required to sign a confidentiality agreement.