The Clean Energy and Vehicle Research Center at the University of South Florida (USF) is operating a 20 kW (peak) photovoltaic (PV) system in which PV panels form the roof of a 12 bay carport. 4 of the 12 bays has a potential 6kW output that can be used for simultaneous computer controlled direct DC-DC charging and utility interconnection. The program has been created to evaluate the potential contribution of photovoltaics as a method for offsetting the fuel cost of electric vehicles while reducing air pollution generated by power plants, that are fueled by non-renewable sources.When charging lead acid batteries in an EV, a large percentage (22%-40%) of the charging power is lost, which raises the cost of operation. The charger losses usually include power conditioning, power factor, and heat losses, which cumulatively can range between 3%-25%. Manufactures neglect the losses that occur inside of the battery pack when testing chargers to quantify their efficiencies. The battery pack is usually assumed to have an inherent 20% loss when accepting charging power. However, this 20% loss is not a constant and can be affected by the charging process.To determine the impact that charging has on battery losses, two chargers with different power conditioning and charging algorithms will be used under controlled conditions. The battery pack is a 120V 183Ah (5 hr rate) flooded lead acid system located in a Chevy S-10 EV. The first charger (charger A) derives its power from the 6kW photovoltaic array. This charger is computer controlled and prevents gassing throughout the entire charge. This power is pure DC with no ripple. The second charger (charger B) derives its power from the 208V single phase AC grid. This power is condition through a transformer and then rectified with no filtering. The charger conducts only when the rectified voltage exceeds that of the battery pack, which results in the output consisting of current ripples. Duringthe last 20% of charge the power is not reduced at a rate adequate to prevent gassing. Test results will be presented to show the extent the ripple power of charger B causes losses in the battery pack, how it influences the battery temperature and the extra losses associated during the gassing phase.
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