To provide an energy storage device capable of precisely obtaining a capacitance value of an electric storage part.
The energy storage device includes: the electric storage part 23 including a capacitor connected between a main power supply 15 and a load 17; a charging and discharging circuit 19 connected to the electric storage part 23 and a voltage detection circuit 25; and a control circuit 41 connected with them. The control circuit 41 obtains in advance a variation range width (Vcr) in a voltage (Vc) of the electric storage part 23 when the load 17 is operated by the electric storage part 23, charges or discharges the electric storage part 23 with a constant current value (I), obtains a time width (Δt) in which the voltage (Vc) of the electric storage part 23 detected by the voltage detection circuit 25 reaches the variation range width (Vcr) from charging and discharging start time, calculates an inclination (ΔVs) of the voltage (Vc) of the electric storage part 23, and obtains a capacitance value (C) of the electric storage part 23 by dividing the constant current value (I) by the inclination (ΔVs).
HAMAI HIDEAKI
Hiroki Naito
Daisuke Nagano
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