Download Normalization and Conditioning of Nickel Metal Hydride Batteries

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
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.
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 1114, 2000. Improved Charge
Algorithms for Valve Regulated LeadAcid Batteries, E Sexton Et Al. Page
211.
• John Rivera (Technician) and Jon
Marshall (Engineering Group Leader),
Curtis Instruments, Inc. Mount Kisco,
NY.
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
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