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Efficient Charging Methods for Nickel Metal Hydride Batteries

Learn about normalization and conditioning methods for NiMH batteries, types of charges, termination methods, factors affected by charging, and examples of charge profiles. Discover future research on charging current vs. temperature and present technology in battery charging.

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Efficient Charging Methods for Nickel Metal Hydride Batteries

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  1. NORMILIZATION AND CONDITIONING OF NICKEL METAL HYDRRIDE BATTERIES By Chris Harrison

  2. 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

  3. 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”.

  4. Trickle charge movie

  5. CHARGE TERMINATION TYPES • Time • Voltage • Temperature and ∆Temperature • ∆Voltage FACTORS EFFECTED BY CHARGING • Charging Efficiency• Charging time • Battery Life • Battery Capacity • Battery Performance

  6. EXAMPLES 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.

  7. REVIEW OF THE LITERATURE • 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.

  8. METHODS 1 - Determine how many Amp Hours to charge or discharge from the battery / battery pack 2 - Calculate time and current for charge 3 - Determine what charge would be best to normalize batteries 4 - Determine termination type 4 - Insert batteries into holder 5 - Set up apparatus for desired parameters 6 - Start monitoring charge statistics (e.g. current, voltage) 7 - Start charge 8 - Analyze end float voltages, and prepare for next charge or discharge based of collected data

  9. FUTURE RESEARCH 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

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