Team AutoVolt

1. Team AutoVolt Preliminary Design Review Team Members: Chris Douglas – Project Manager David Hooker – Lead Research, Webmaster James Randall – Liaison, Budget Manager Sponsors: Naval Surface Warfare Center: Acoustic Research Detachment, Bayview ID Advisor: Dr. Gregory Donohoe, University of Idaho Mentor: Dr. Herbert Hess, University of Idaho

2. Agenda Problem Statement, Specifications, Deliverables Current System, Situation Design Concepts Trade Study Equipment Return on Investment Timeline/Future Work Challenges

3. Problem Statement (ARD) has requested improvement of capacity retention over the course of the propulsion batteries life cycle. The Large Scale Vehicle 2 (LSV2) is an autonomous electric submarine used to study acoustic properties of propulsion systems. The Acoustic Research Detachment

4. Specifications Document current charging configuration with scheme advantages and disadvantages Research of potential changes to system to extend capacity retention Develop a cost-benefit analysis of implementing a new charging scheme Produce computer simulations of current and alternate configurations Construct lab scaled model of current and alternate schemes

5. Deliverables Current System Report Trade Study Selected Choices Summary Overview of Rejected Proposals Cost-Benefit Report Lab Test Report Proof of Safety Report Computer Simulation

6. Current Charging Method Main Charge Overcharge 1. CC(45A/string) until 2.35V/cell 2. CV until 6.25A/string 3. CC for 3 hours with 2.50V/cell voltage limit 2.50V/cell voltage limit 1680 2V batteries divided into 4 parallel strings Approximately 15min checks Batteries decommissioned @ 4 years(approx. 80% capacity)

7. Situation • Human charge control can lead to undercharge or overcharge • Both OC and UC can lead to battery life degradation • Charging infrastructure maxed • Chargers working at max current • wiring from chargers to sub at max current • Power grid already overloaded • Aux. battery charge ~ 12 hours • Two types of chargers readily available

8. Potential Improvements/Benefits • Extend useful life of batteries • Reduce expenses over long term • Reduce submarine downtime over long term resulting in higher return for taxpayer dollars • Reduce the capacity loss of batteries over current service life • Maintain underway duration over service life

9. Improvements/Benefits (cont) • Automate System • Free up technicians for other purposes • Reduce risk of error of human control • Improve Oxygen recombination efficiency(ORE) • Reduce outgassing • Decrease energy waste

10. Solution Concept #1 ΔVoltage • Zero Delta Voltage (ZDV) • Concept • Max current charges until 70% return of charge • Constant Current (C/5) until ZDV is reached • ZDV is defined as a limit in change in voltage between two readings • A reading is defined as 30 second averages of voltage readings

11. Zero Delta Voltage • Pros • Accurately detects end of charge cycle • Reduces human error during charge cycle • Reduces possibility of detrimental undercharge/overcharge • Possible 100% increase of battery life • Cons • Will need to be tested on multiple battery system • Variable voltage termination limit over life of batteries

12. Solution Concept #2 . . . • Current Interrupt (CI) • Concept • Used after primary charge has completed (overcharge) • Charge algorithm consists of a pulsed current • CI is employed until 10% overcharge has been achieved

13. Current Interrupt • Pros • Allows cooling period for batteries preventing excessive thermal degradation • Allows for chemical reactions to stabilize during the off period leading to higher ORE • Can be used independently of main charge method • Cons • Unknown change in charge time • Setup of system may be complex • Normally employed after a fast charge algorithm has delivered 100% of depleted charge

14. Solution Concepts #3 • Fast Charging • Start with large current pulses (up to 4C) • Monitor voltage and step down current each time voltage limit is reached

15. Fast Charging • Pros • Is an extremely fast charge method • Increases capacity retention throughout life • Cons • Requires enormous amounts of current (up to 600A) • Generates large amounts of heat

16. Trade Study 39%

17. Unknowns in Trade Study CI and ZDV require testing Charge module capabilities unknown Testing is required to determine charge time Long term effects to be determined

18. Timeline/Future Work #1

19. Computer Simulations • Software capable of accurately simulating cycle life has yet to be discovered • State of health simulation is unfeasible at this time due to: • Varying discharge rates during each test run • Varying internal characteristics and chemical composition over battery life • Varying and unknown cell temperatures for charge and discharge cycles • Development contingent upon lab data

20. Equipment

21. Return on Testing Investment Continued use of system Benefits of New system • $593,000/4 years for Main battery replacement • Labor costs of replacement process • Extending battery service life by at least 50% yields savings of $50,000/year (not including man hours) • Length of underways can be maintained over longer period of time yielding more data collected per run

22. Challenges State of health simulations non-existent Time constraints for cycle life testing Managing multiple test cases Access to charger control module Access to /Purchase of testing equipment

23. Alternative Timeline Schedule with design of charge/discharge system Alternative budget to be determined

24. Questions?