The following paper discusses the current status of ongoing testing of FNCVR (valve regulated) cells. This valve regulated nickel cadmium battery design is unique in that it incorporates two phases of recombination of gases generated during charge. A low-pressure vent is used to enhance recombination of oxygen at the negative plate as well as an internal catalyst, which is used in the headspace of the cell. The vent design and catalyst were jointly developed by Hoppecke Batteries Inc. and Philadelphia Scientific. The use of the catalyst allows for the use of higher charge voltages than that used by other cell designs with valve regulation only. This allows the cell to function with the same characteristics of a flooded/vented cell and allows for faster recharge and operation at a higher state of charge.

Two (2) FNCVR cells have been on charge in a temperature chamber for more than 360 days at 90 deg F. Several control cells consisting of standard flooded/vented FNC cells of the same amp-hour capacity have been on charge concurrently with the FNCVR test cells. The cell charge voltages for the FNCVR test cells and the control cells are 1.45 volts per cell.

After 340 days, the FNCVR and control cells were capacity tested to determine if there was any degradation of performance over the previous test period. After the capacity test, both groups of cells were recharged using constant voltage (1.52vpc) for 8 hours and then returned to the float voltage setting of 1.45vpc.

The following Figure 1 shows the gas (hydrogen & oxygen) collected (in ml) for the control and FNCVR cells. Figure 1 is the average data for the 3 control cells and 2 FNCVR test cells.

From the graph it is clear that almost no gas was generated by the FNCVR cells over the first 340 days prior to the capcity test. After the capacity test some gas is evolved due to the recharge at the higher voltage and then stabilizes again once the cells are returned to float charge.

Figure 2 shows the individual results of the 6 hour discharge capacity test. The test was terminated at the 6 hour point and all control and FNCVR cells had capacities in excess of 100% of their nominal capacity.

The flooat charge current was recorded as part of the normal data collected. The data in Figure 3 shows the average float current of the FNCVR cells and the control cells during the test period. There is a slight depression of the float charge current for the FNCVR cells. However, it is not clear at this time if this difference is significant or merely variation in the cells internal resistance.

CONCLUSIONS:

Based on the water loss from the gas collection results at the elevated temperature (Figure 1) it is clear that the performance of the valve and catalyst recombination is better than that predicted in the original design testing. The maintenance interval expected at 90 deg F and 1.45vpc charging based on the design criterial specified in Figure 4 is approximately 5 – 6 years. Based on the actual test results from Figure 1 the actual expected maintenance interval for these parameters is in excess of 10 years. Based on this it can estimated that the FNCVR will have a 20 year maintenance interval at the higher charge voltage of 1.45vpc and 68 deg F and a 40 year maintenance interval at a float voltage of 1.42vpc and 68 deg F.

The results at this point are very good and indicate results better than expected overall from the original design.

Testing will continue with the current set up for at least 6 more months and possibly 12 months before any changes are made to the test parameters.

HOPPECKE has developed a new process that is capable of enhancing the capacity of the FNC (fiber plate nickel cadmium) battery technology.

This process has been introduced into the Production of cells with the newly released range of long rate discharge (L-type) cells. The new cell designations for these Types reflect the enhanced cell capacity (i.e., FNC 176 L – 176 Ah).

This process, developed by HOPPECKE, is unique to the FIBER Plate design of the FNC product and is only available from HOPPECKE. Over 5 years of concentrated research has led to the development of this special process which allows HOPPECKE to produce cells with approximately 10% added capacity and at the same time reduce overall active material cost in the battery. The result is a better performing battery as far as capacity and medium rate discharge rates are concerned as well as providing enhanced recharge efficiency.

The development of this Process is part of HOPPECKE’s ongoing Innovation Initiative for continued development of the FIBER Plate technology for nickel cadmium and nickel metal hydride products.