© Philadelphia Scientific 2004 A Case Study: Four Years of Performance Data at a Canadian Rehydration and Catalyst Addition Site Harold A. Vanasse – Philadelphia Scientific Robert Anderson – Anderson’s Electronics Philadelphia Scientific

© Philadelphia Scientific 2004 Presentation Outline Site Description. Process Description. The Science Behind the Process. Site Results. Financial Impact. Trends from 10,000 cells.

© Philadelphia Scientific 2004 Site Description Central Office site owned by a major telecom. One string of 24 cells. –“20-Year Design” VRLA Product. –900 Ah cells. –Major US Manufacturer. Cells were installed in Temperature controlled at 21 – 27 ºC.

© Philadelphia Scientific 2004 Site Description Good maintenance practices followed. –Dedicated power technicians. –Annual re-torqing of intercell connectors. –Semi-annual conductance testing, voltage measurement and visual inspection. About as good as it gets for batteries!

© Philadelphia Scientific 2004 Test Site as found in 2000 Slight bulging of jar cover indicating positive plate growth – not severe at all. Capacities near 5%! Customer not happy.

© Philadelphia Scientific 2004 Decision Process Scrap cells and replace with new cells. OR Try adding water & catalysts and save the cells.

© Philadelphia Scientific 2004 Decision Process Decision: Water and catalysts were added to each cell as a test of the process. Telecom felt they had nothing to lose.

© Philadelphia Scientific 2004 Process Steps Philadelphia Scientific

Step 1: Cell Inspection

© Philadelphia Scientific 2004 Cell Inspection Cell Leaks: The cell must pass a pressure test in order to qualify. Physical damage: Positive Plate growth should not be in an advanced stage – no severely bulging jars or covers. Cell voltage measurement. Cell temperature measurement.

© Philadelphia Scientific 2004 Process Steps Continued 2.State of health determined. –Ohmic measurements. –Capacity Test. 3.Cells Rehydrated -- Water added to each cell. 4.Catalyst Vent Cap installed into each cell. 5.Annual follow-up inspections.

© Philadelphia Scientific 2004 What Happens Inside the Cell at Each Step? (This is the technical section!)

© Philadelphia Scientific 2004 What Water Addition Does – Part 1 Dry out occurs because oxygen and hydrogen gas vent from the cell over time. As float current rises dry out process accelerates. The water that was added replaced the water that was lost. –Maintains proper electrolyte.

© Philadelphia Scientific 2004 What Water Addition Does – Part 2 When glass mat separator dries out it shrinks. –Electrical contact between plates is disrupted (conductance lower). Water added is absorbed by glass mat. Glass mat swells like a sponge and restores electrical contact between plates. –Conductance higher/better.

© Philadelphia Scientific 2004 What Catalyst Addition Does Negative plate self discharge is a fundamental problem with VRLA cells. Too much oxygen reaches negative plate and causes it to discharge. This occurs while battery is on float charge! Polarization of individual plates tells the story.

© Philadelphia Scientific 2004 What is Polarization? A measure of the voltage on the positive plate and the voltage on the negative plate. Cell over-voltage is divided between positive and negative plates. We want to know how the voltage is distributed among the plates.

© Philadelphia Scientific 2004 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 cell’s self-discharge.

© Philadelphia Scientific 2004 Polarization of Plates Results of a long term lab test serve as example. 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

© Philadelphia Scientific 2004 The Positive Plate and the Lander Curve Optimum Positive Plate Polarization

© Philadelphia Scientific 2004 Tafel Curve A diagram that relates polarization and current … among other things. The next slide shows: –The difference between a healthy and non- healthy distribution of voltage. –How a decrease in positive plate polarization leads to lower cell current.

© Philadelphia Scientific 2004 Tafel Curve Series

© Philadelphia Scientific 2004 Catalyst Addition 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.

© Philadelphia Scientific 2004 Putting It All Together

© Philadelphia Scientific 2004 Ongoing Inspections Site inspected each September from 2001 to Parameters: –Visual inspection. –Conductance. –Capacity Test. –Temperature. –Float Voltage.

© Philadelphia Scientific 2004 September 2004: Positive Plate Growth Not Progressing

© Philadelphia Scientific 2004 Site Conductance Change

© Philadelphia Scientific 2004 Site Load-Test Run Time Change (Minutes before 1.90 VPC at 3 Hour Rate)

© Philadelphia Scientific 2004 Site Run Time Change (Minutes at Actual 62 Amp Load -- Calculated)

© Philadelphia Scientific 2004 Anecdotal Evidence During the August 2003 blackout the battery string at this site did not drop the load. Site was powered by the battery for 5+ hours until generator arrived and was on-line.

© Philadelphia Scientific 2004 Test Site Data Interpretation Immediate improvements (within 6 months) result of water addition. Long term improvements (6 months to 4 years) result of catalyst addition. The improvements are still being maintained after 4 years. Site load being protected for the required amount of time (8 hours).

© Philadelphia Scientific 2004 Financial Impact This string was about to be recycled, however 4 years later it remains in service. The end user did not need to buy new cells for this site – this purchase has now been deferred for 4 years.

© Philadelphia Scientific 2004 Financial Impact Based on a financial analysis of actual work at over 375 sites across multiple customers in North America: –For every $1,000 spent on this process $13,000 has been deferred in battery replacement costs. –Typical payback in 4 to 8 months.

© Philadelphia Scientific 2004 Another Way to Look at the Financials Assume: –Site equipment has 20 year life. –Batteries have 7 year life. 3 strings of batteries will be purchased throughout the life of the site. If batteries can last 10 years only 2 strings would be purchased. Test site is now at 11 years of life. The requirement to purchase 1 string of batteries has been eliminated.

© Philadelphia Scientific 2004 Trends from 10,000 Cells Rehydration and catalyst addition process completed on 10,000 cells so far. Ages range from 1993 to Four trends identified: 1.Cell dry out (or loss of compression) starts earlier then most people believe.

© Philadelphia Scientific 2004 Trends from 10,000 Cells Trends continued: 2.New cells are not immune to the problems presented. Negative Plate Self Discharge begins within the first few years. 3.Ohmic measurements (conductance, resistance, impedance) are good tools to identify problems if data is trended. 4.By customizing the amount of water added to each cell uniform recovery can be obtained across an entire string.

© Philadelphia Scientific 2004 One Last Bit of Data 180 cell UPS Site Internal Resistance data trended over the last 7 years. Water and Catalysts added in Improvements seen in resistance measurements.

© Philadelphia Scientific Cell UPS Site Average Internal Resistance (mOhms)

© Philadelphia Scientific 2004 Conclusions VRLA Cells can be recovered from Negative Plate Self Discharge. Water and Catalyst Addition process can defer replacement of cells that are “failing”. Our test site is still looking good after 4 years. Ohmic measurements can provide early warning if data is trended.