This paper describes the design and construction of a 320-V, 12-F EDLC energy storage bank connected to a bidirectional isolated dc-dc converter. A trade-off between two types of EDLC bank configurations is considered with focus on voltage balancing circuits. This paper also proposes a center-tapped- transformer voltage balancing circuit for the EDLC bank, and includes its experimental verifications. Following that, the experimental charge-discharge characteristics of the EDLC energy storage system, along with a self-starting result is discussed. The power loss in the voltage balancing circuit in the charge-discharge operation is found to be negligibly small. An observed low ripple current flowing into the EDLC bank is also theoretically analyzed.