1. © Philadelphia Scientific 2002 Philadelphia Scientific Catalysts in Canada: The Science Behind 2 Years of Canadian VRLA Cell Rehydration and Catalyst Addition Harold A. Vanasse – Philadelphia Scientific Robert Anderson – Andersons Electronics Philadelphia Scientific

2. © Philadelphia Scientific 2002 Philadelphia Scientific Presentation Outline An example of real batteries Polarization made simple How a cell works with a catalyst Two years of Canadian field data Fine tuning rehydration

3. © Philadelphia Scientific 2002 Philadelphia Scientific Overview

4. © Philadelphia Scientific 2002 Philadelphia Scientific A Tale of Two Batteries Test has been running for 6 years. All cells at 90ºF and 2.27 VPC. 2 Groups of 6 cells each. High Quality 2 Volt VRLA AGM Cells.

5. © Philadelphia Scientific 2002 Philadelphia Scientific A Tale of Two Batteries Parameters Frequently Measured: Gas evolved. Conductance Capacity Polarization Float Current Cells never boost charged --- just float charged!

6. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Cell Tear Down Tear down analysis of all but two catalyst cells conducted in years 4 & 5. Catalyst cells looked great. Non-Catalyst cells had: –Massive corrosion of negative grid. –Dry out.

7. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Capacity

8. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Gas Evolution

9. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Conductance

10. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Float Current

11. © Philadelphia Scientific 2002 Philadelphia Scientific Why is Float Current Important? A lowered float current is beneficial to the cell … but not just by adjusting the charger. Lowered float current reduces: –Positive plate corrosion. –Amount of gas generated by the cell (Water loss). –Cell dryout (better conductance). –Risk of thermal runaway.

12. © Philadelphia Scientific 2002 Philadelphia Scientific What did we find? Polarization of Plates Non-catalyst cell: All the overvoltage is on the positive. Catalyst cell has a better distribution. Non-Catalyst Cell Catalyst Cell Neg.0 mV-20 mV Pos.120 mV100 mV

13. © Philadelphia Scientific 2002 Philadelphia Scientific Polarization Made Simple A reference electrode measures the voltage on the positive plate and the voltage on the negative plate. Combining these two voltages gives you the total cell voltage. A depolarized plate is not good for the cell.

14. © Philadelphia Scientific 2002 Philadelphia Scientific And Now For Some Math … An example: Float Voltage 2.27 Volts Open Circuit Voltage2.15 Volts Overvoltage0.12 V or 120 mV The overvoltage is what overcomes the cells self-discharge.

15. © Philadelphia Scientific 2002 Philadelphia Scientific Polarization Fundamentals Using a reference electrode we can determine how the overvoltage is split among the plates. Optimally, the positive plate receives the majority. –Too little and it wont charge properly –Too much and corrosion will be accelerated.

16. © Philadelphia Scientific 2002 Philadelphia Scientific Lander Curve Optimum Positive Plate Polarization

17. © Philadelphia Scientific 2002 Philadelphia Scientific Tafel Curve A diagram that relates polarization and current … among other things. The next slide shows how an increase in positive plate polarization leads to higher cell current. Warning: Electrochemical diagram ahead!

18. © Philadelphia Scientific 2002 Philadelphia Scientific Tafel Curve Series

19. © Philadelphia Scientific 2002 Philadelphia Scientific Lessons from the Tafel Positive plate polarization and float current are directly related. Lower positive plate polarization leads to lower float current. If negative plate is polarized it will automatically reduce the polarization on the positive plate. This leads to lower float current.

20. © Philadelphia Scientific 2002 Philadelphia Scientific Remember what we found? Non catalyst cells had higher float current because all of the overvoltage was on the positive. Catalyst cells had lower float current because overvoltage was distributed. Non-Catalyst Cell Catalyst Cell Neg.0 mV-20 mV Pos.120 mV100 mV

21. © Philadelphia Scientific 2002 Philadelphia Scientific Take Home Point Keeping the negative plate polarized is the key to lowering the float current.

22. © Philadelphia Scientific 2002 Philadelphia Scientific How does a catalyst help do this? Must start with some VRLA basics: –H 2 produced on the negative plate. –O 2 produced on the positive plate. –O 2, hydrogen ions and electrons recombine on the negative plate to form water.

23. © Philadelphia Scientific 2002 Philadelphia Scientific How does a catalyst help do this? –When O 2 reaches negative plate it causes a reduction in the polarization. –While the cell is on float, a portion of the charge current will try to polarize the negative. There is a balancing act between the last two points

24. © Philadelphia Scientific 2002 Philadelphia Scientific Putting it all together By placing a catalyst into a VRLA cell: –A small amount of O 2 is prevented from reaching the negative plate. –The negative stays polarized. –The positive polarization is reduced. –The float current of the cell is lowered.

25. © Philadelphia Scientific 2002 Philadelphia Scientific Science Summary The catalyst prevents some oxygen from reaching the negative plate. Too much oxygen reaching the negative plate causes depolarization. A depolarized negative plate causes a higher cell current due to excessive polarization of the positive plate. Test shows better performance in cells with catalysts.

26. © Philadelphia Scientific 2002 Philadelphia Scientific Catalysts in Canada Andersons Electronics has been adding water and catalysts to VRLA cells in Canada for over two years. The following data was collected by Andersons from sites in Canada.

27. © Philadelphia Scientific 2002 Philadelphia Scientific What is Rehydration? Rehydration is adding water to VRLA Cells that have dried out. Contact between AGM and plates is restored as AGM swells with water. Improved ohmic measurements and capacity are generally observed. Improvements are only temporary until cell dries out again.

28. © Philadelphia Scientific 2002 Philadelphia Scientific Fine Tuning Rehydration A consistent amount of water is usually added to each cell. Two years of field experience has resulted in a more precise method. All cells dont dry out at the same rate. A unique amount of water is added to each cell to optimize rehydration.

29. © Philadelphia Scientific 2002 Philadelphia Scientific Conductance without Tuning

30. © Philadelphia Scientific 2002 Philadelphia Scientific Conductance with Tuning

31. © Philadelphia Scientific 2002 Philadelphia Scientific Why Tune Rehydration? Cells in a string do not dryout at the same rate. A more consistent end result for all cells in the string. Too much or too little water is never added.

32. © Philadelphia Scientific 2002 Philadelphia Scientific The Real World Two test sites in Canada each two years old. All cells are VRLA from 1993 and same manufacturer. Data collected from these sites: –Conductance –Capacity –Run Time Catalysts and water added to each cell.

33. © Philadelphia Scientific 2002 Philadelphia Scientific P Site Conductance Change

34. © Philadelphia Scientific 2002 Philadelphia Scientific P Site Capacity Change

35. © Philadelphia Scientific 2002 Philadelphia Scientific P Site Load Test Run Time Change (Minutes before 1.90 VPC at 3 Hour Rate)

36. © Philadelphia Scientific 2002 Philadelphia Scientific W Site Conductance Change

37. © Philadelphia Scientific 2002 Philadelphia Scientific W Site Capacity Change

38. © Philadelphia Scientific 2002 Philadelphia Scientific W Site Load Test Run Time Change (Minutes before 1.90 VPC at 3 Hour Rate)

39. © Philadelphia Scientific 2002 Philadelphia Scientific Technical Summary Conductance is improved and maintained for two years thus far. Capacity is greatly improved and maintained for two years thus far. Run time is restored and now meets customer requirements. –8 hours of real run time.

40. © Philadelphia Scientific 2002 Philadelphia Scientific Common Sense Summary This customer did not need to replace the batteries. They have lasted two years longer than expected and will most likely continue. Deferred capital expenditure. The procedure was successful. The Customer Was Happy!

41. © Philadelphia Scientific 2002 Philadelphia Scientific Conclusions Water added to cells gives immediate improvements. Catalysts maintain the improvement because the root cause is addressed. Catalysts prevent negative plate from depolarizing, which lowers float current. Batteries remain in service longer. Water and Catalysts must be added together.

42. © Philadelphia Scientific 2002 Philadelphia Scientific Thank You Philadelphia Scientific