Project

# Title Team Members TA Documents Sponsor
55 Solar Powered Rechargeable Battery Pack with Controllable Voltage Output
 Zhuohang Cheng
Zihao Zhang
 Bryce Smith design_document0.pdf
final_paper0.pdf
presentation0.pptx
proposal0.pdf
Team Members:

Zhuohang Cheng (zcheng14)

Zihao Zhang (zzhng130)

Project Description:
This project involves a rechargeable battery pack with following features:
1. Will have a solar panel as power source which can constantly provide dc power to the battery pack when the user is doing outdoor activities.
2. Can also be charged by the power grid with 110V.
3. Can discharge AC or DC power with adjustable voltage level, from 5V to 25V DC, and from 20V to 120V AC.
4. Will have battery management system to indicate the voltage level, output current and charge/discharge condition.

Project Uniqueness:
The rechargeable battery packs are not user-friendly today. Most of them can only output one voltage level, and users need to buy extra voltage converter to fit their device. We would like our battery to output adjustable voltage level which could satisfy every device for our users. Also, it can provide constant power in daytime without concerns of out of battery.

Project Requirements:
For this project, we need to build a storage battery pack using several parallel-connected rechargeable batteries. Converters and inverters will be needed to regulate the input and output voltage. A portable box with surface-mounted solar panel provides the flexibility of outdoor activities. To monitor and control the discharging process, a microcontroller with display screen will be necessary for user interaction.

Active Cell Balancing for Solar Vehicle Battery Pack

Tara D'Souza, John Han, Rohan Kamatar

Featured Project

# Problem

Illini Solar Car (ISC) utilizes lithium ion battery packs with 28 series modules of 15 parallel cells each. In order to ensure safe operation, each battery cell must remain in its safe voltage operating range (2.5 - 4.2 V). Currently, all modules charge and discharge simultaneously. If any single module reaches 4.2V while charging, or 2.5V while discharging, the car must stop charging or discharging, respectively. During normal use, it is natural for the modules to become unbalanced. As the pack grows more unbalanced, the capacity of the entire battery pack decreases as it can only charge and discharge to the range of the lowest capacity module. An actively balanced battery box would ensure that we utilize all possible charge during the race, up to 5% more charge based on previous calculations.

# Solution Overview

We will implement active balancing which will redistribute charge in order to fully utilize the capacity of every module. This system will be verified within a test battery box so that it can be incorporated into future solar vehicles.

Solution Components:

- Test Battery Box (Hardware): The test battery box provides an interface to test new battery management circuitry and active balancing.

- Battery Sensors (Hardware): The current battery sensors for ISC do not include hardware necessary for active balancing. The revised PCB will include the active balancing components proposed below while also including voltage and temperature sensing for each cell.

- Active Balancing Circuit (Hardware): The active balancing circuit includes a switching regulator IC, transformers, and the cell voltage monitors.

- BMS Test firmware (Software): The Battery Management System requires new firmware to control and test active balancing.

# Criterion for Success

- Charge can be redistributed from one module to another during discharge and charge, to be demonstrated by collected data of cell voltages over time.

- BMS can control balancing.

- The battery pack should always be kept within safe operating conditions.

- Test battery box provides a safe and usable platform for future tests.