The standard Magnecharger is rated to operate from an AC supply ranging from 208 to 240 volts. It is designed to draw a constant 30A regardless of the input voltage, so less power is available when fed from 208v than from 240v and charging times are about 15% longer.
This is readily seen in battery pack charging current as monitored by a PDT (Portable Diagnostic Tool) or Peter Ohler's PilotDash. A charger operating from 240v typically produces 17.5-18.0 amps into a PbA battery at an intermediate state of charge, while a charger operating from 208v typically produces only 14-15 amps.
In North America, standard residential utility power is single phase 120/240v AC. More accurately, this is two-phase power, with two "line" ("phase" or "hot") wires and a grounded neutral. Each line is at 120v with respect to ground. Since the two line wires are 180 degrees out of phase with each other, between the line wires you see twice 120v, or 240v. This lets most residential magnechargers operate at full power.
But in commercial establishments, "three-phase" power is the norm. The common "three-phase 120/208v wye" configuration provides three line wires and a grounded neutral. While each line wire is 120v with respect to ground as in residential service, the voltage between each pair of line wires is only 208v. Why? Because the three line wires are only 120 degrees out of phase with each other (360 degrees in a circle / 3 phases = 120 degrees/phase).
A little trigonometry will show that the voltage between two phases that are 120 degrees apart is sqrt(3) = 1.73 times the voltage of one phase to ground. So if the phase-to-ground voltage is 120v, the phase-to-phase voltage is 1.73 * 120v = 208v.
Note: EV1s with Panasonic ("advanced") PbA packs limit charging current to 16A, vs 18A for the original Delphi PbA packs. This lessens the difference between 240V and 208V powered chargers. Also, charging currents for NiMH batteries are lower than for PbA because of the higher nominal NiMH pack voltage: 343V for NiMH vs 312V for PbA. The charging power, which is what matters, is the same for both.
Last updated: 23 Aug 2000 by Phil Karn