2017/5/15 · Manufacturer efficiency curves may show drop-off in efficiency occurring at low currents, but do not graph for differences in voltage. For example, the manufacturer's specification sheet for the charger tested here [34] shows 208 V A C charging at the lowest efficiency of 80% at 1 kW (5Amps), moving up to 90% at 2.5 kW (12Amps), and reaching 95% efficiency above 6 kW (30Amps).