Design and Experimental Testing of a Battery Balancing System for Lead-acid Batteries

Open Access
Author:
Melville, Christopher Martin
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 15, 2013
Committee Members:
  • Christopher Rahn, Thesis Advisor
Keywords:
  • Lead-Acid
  • Batteries
  • Balancing
  • BMS
  • VRLA
  • Degradation Modes
Abstract:
Lead-acid batteries are ubiquitous, comprising the most popular rechargeable battery chemistry, widely used in stationary, EV, and HEV applications. Valve-regulated lead-acid batteries (VRLAs) are particularly popular for a variety of characteristics including reduction of spills and dangerous fumes, prolonged operating life and efficiency due to features such as immobilized electrolyte and catalytic recombination of evolved hydrogen and oxygen, vibration resistance, and resistance to lead dendrite formation. While these benefits confer a substantial advantage to VRLAs, they are still susceptible to manufacturing flaws, progressive degradation and user abuse. Many batteries, particularly large strings with high power and frequent cycling requirements, have a battery management system (BMS) to monitor and protect against overcharge, over discharge, excessive current rates, extreme temperatures, cell imbalance and other safety factors dependent on the battery chemistry. In this thesis, a battery balancing system is developed to demonstrate the lifetime battery benefits of maintaining cell balance. This thesis demonstrates that the developed cell switching system (CSS) can bring the cells of a battery into SOC balance and hold them there using an algorithm designed to charge the most unbalanced cells first.