February 2002
Electric Applications Inc. (EAI) staff has been developing infrastructure for the operation of electric vehicles for over 10 years. They have developed partial-state-of-charge (PSOC)/fast-charge strategies for a variety of lead-acid battery powered electric vehicles (EVs). This type of duty has been shown to decrease charge times to 10-30 min, whilst retaining if not improving battery cycle-lives. Recent developments have included vehicles and operating systems for electrically powered ground-support equipment (GSE) at airports. The gelled-electrolyte valve-regulated lead-acid (VRLA) batteries currently used for GSE vehicles are expensive and have a high internal resistance. This leads to significant heating of the batteries during charging and also extended charge times (up to 1 h). To address these issues, PNW have evaluated the performance of an alternative technology manufactured by Sonnenschein that has both a reduced cost and a lower internal resistance. The batteries, called Dryfit, are a 6-V monobloc with a 1C capacity of 110 Ah. This report describes the evaluation of two GSE vehicle battery packs that comprise 28, Dryfit modules, configured in two, 84-V strings, under simulated GSE service. Both a brand-new pack, and a pack retrieved from the field have been tested. The latter had been in service at the Phoenix airport for over 18 months and had performed an estimated 350 GSE cycles. The new and old packs were subjected to 204 and 24 days of simulated GSE service, respectively. The performance of both packs during these cycling periods was excellent. Indeed, the capacity provided by the old pack matched that of the new. The excellent condition of the old pack was confirmed by a series of standard 1C discharge/charge cycles ¾ the capacity obtained during these experiments was at least equal to that of the nominal value. Given the service life already provided by the old pack (see above), it is considered conservative to predict a lifetime in the field of over three years.
