NORMILIZATION AND CONDITIONING OF

NICKEL METAL HYDRRIDE BATTERIES

By Chris Harrison

INTRODUCTION• Charging is the way to restore energy back into batteries that are “empty”.

• Rechargeable batteries are important because they can be reused. • Batteries can be charged in many ways to produce certain results. - Charge #1 fast charges batteries for electric vehicles applications.- Charge #2 recovers batteries that have been unused for an extended period of time.

•Charges affect many important battery aspects:- Battery Life - Battery Capacity - Battery Performance

BATTERY EFFECTS• Internal Battery Resistance - As the battery gets increasingly “full”, it becomes harder to squeeze in the remaining energy.

• Self Discharge - Batteries naturally decrease in energy as chemicals slowly react inside the battery.

SIMPLE CHARGE TYPES• Constant Current- Charges at a certain current for a specified time.- As internal battery resistance increases and current does not drop, temperature can increase. This may damage the battery and be a safety hazard. • Trickle Charge- Same as constant current, but uses very low currents. - Low current allow “full” batteries resist further charging while empty batteries “catch up”.

Trickle charge movie

CHARGE TERMINATION TYPES• Time

• Voltage

• Temperature and ∆Temperature

• ∆Voltage

FACTORS EFFECTED BY CHARGING• Charging Efficiency • Charging time

• Battery Life

• Battery Capacity

• Battery Performance

EXAMPLE PROFILE 1: Begins charge with a high initial current and then drops to a lower current.

POSSIBLE RESULT: May produce good charge time, but reduces battery performance.

EXAMPLE PROFILE 1: Begins charging with a low current then rises to a high current.

POSSIBLE RESULT: May have poor charge efficiency and damages battery because of extreme heat and reduces battery capacity.

EXAMPLES

• Maintenance-Free Batteries, 2nd Edition, D. Berndt, Research Studies Press Ltd., Somerset, 1997. •The Fifteenth Annual Battery Conference on Applications and Advances (Proceedings), California State University, Long Beach, Jan 11-14, 2000. Improved Charge Algorithms for Valve Regulated Lead-Acid Batteries, E Sexton Et Al. Page 211.

• John Rivera (Technician) and Jon Marshall (Engineering Group Leader), Curtis Instruments, Inc. Mount Kisco, NY.

REVIEW OF THE LITERATURE

1 - Determine how many Amp Hours to charge or discharge from the battery / battery pack2 - Calculate time and current for charge3 - Determine what charge would be best to normalize batteries4 - Determine termination type4 - Insert batteries into holder5 - Set up apparatus for desired parameters 6 - Start monitoring charge statistics (e.g. current, voltage)7 - Start charge8 - Analyze end float voltages, and prepare for next charge or discharge based of collected data

METHODS

CHARGING CURRENT VS. TEMPERATURE• Intense Charging - More current flows through wires and battery - Generates lots of heat - Could damage the fragile internal materials

PRESENT TECHNOLOGY• Terminates when: - Threshold temperature is reached - Temperature change reaches a certain slope,• This allows the battery to cool• Resumes the charge until it reaches that temperature again. • These pauses waste time.• Stop-and-go charging could damage the battery.

FUTURE RESEARCH - Temperature regulated charge algorithms

FUTURE RESEARCH