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The 14/42V Electrical System Architectures have been the subject of discussions in many technical meetings. Some of the major challenges are: system cost, mixed load handling flexibility, jump start issue, battery service life, and transient voltage under load dump situation. In this paper, a patented, bi-directional, charge-transfer circuit is evaluated against these criteria. Circuit performance is discussed in details. It covers circuit efficiency, battery voltage ripple, and transfer-current ripple, and the effectiveness of balancing the battery voltages under various mixed 12/36V loads. The energy transfer principle between a 14V system and a 42V system is presented to demonstrate the cross jumping and surge-load handling capability. The bi-directional energy transfer capability of the circuit easily keeps the load-dump transient-voltage under the 58V limit with either the 14V or the 28V batteries are disconnected.

The Thai Pollution Control Department (PCD) decided in 1994 to pursue the development of a 12-meter hybrid electric bus that would operate successfully in Bangkok environment. The development work began in January 1997. The hybrid-electric bus design concepts are discussed. The hybrid system components and their functions were presented in this paper. The hybrid-electric chassis was first tested in a racetrack near Atlanta in July 1998. Test results were compared to the design data. The hybrid-electric chassis was shipped from Georgia to Bangkok in December 1998. “Real World” testing began in June 1999. The test program was successfully concluded in December 1999. Results were reviewed and problems encountered during the testing as well as appropriate solutions were discussed.