December 2007
Electric Applications staff have been contracted to oversee the manufacture and perform simulated testing of an advanced valve-regulated lead-acid (VRLA) battery under simulated hybrid-electric vehicle (HEV) duty and in a vehicle in the field. One hundred batteries (nominal 27 Ah, 1-h rate) were constructed in conjunction with a local battery manufacturer, and included an optimum negative paste formulation and grid design. Modified batteries were evaluated under a simple and advanced HEV schedule in the laboratory. Their performance was excellent compared to an unmodified baseline unit – modified batteries delivered almost 15,000 cycles with minimal degradation in performance, whereas the unmodified unit experienced considerable polarization during charging and reached the cut-off voltage limit after just 3,000 cycles.A modified battery was evaluated under simulated HEV bus duty – the battery operated trouble-free for 515 250 cycles. In terms of lifetime energy, this cycle life is consistent with the completion of 3300 cycles between 0 and 100% SOC. As the voltage at the end of the major discharge (200 A) only decreased slightly from 11.64 to 11.30 V during testing, it seems likely that over 4000 cycles are likely – note that such a lifetime energy delivery equates to ~70% of that provided by a Prius nickel metal hydride battery over its 160 000 mile design life. This is an excellent performance, given that the profile was based on a 50 Ah module (i.e., the profile was not rescaled to allow for the smaller 30 Ah battery used). Hence, hybrid bus manufacturers can now significantly reduce the size, weight and cost of their battery systems by replacing 50 Ah modules with the same number of 30 Ah units.A drive cycle (termed the ‘Simulated Silverado HEV Schedule) that simulates the operation of a battery pack in a Silverado HEV has been developed. It is based on data obtained from a battery pack in a Silverado during both operation under standard drive cycles on a dynamometer, and actual operation on the road. The profile is designed to apply the same energy and power requirements to the battery as that experienced in the field. A 36-V battery pack comprising modified modules has been evaluated under this schedule for a total of 55 000 simulated miles. During this time, the change in behavior of the battery voltage during charge and discharge was minimal – analysis confirmed that the batteries were in a good condition at the completion of the test, and HPPC testing showed that the ‘all important’ available discharge power had not changed as a result of the cycling. This is considered an excellent result given the abusive nature of the simulated schedule.A 36-V battery pack of modified units has been retro-fitted to a Silverado HEV and then driven around Phoenix for a total of 30 000 miles. The battery performance was trouble-free during this time, and HPPS testing showed that available discharge power had been maintained throughout the test period. In summary, the performance of the modified batteries under simulated HEV bus duty was excellent. They also performed very well under both simulated and field Silverado HEV duty – the results suggest that the ALABC SuperC technology is now ready for.
