deemsh, thank you posting that Vermont study. Interesting what taxpayer $$ get used for.
The study quickly realized that EVSE efficiency is meaningless and I'm surprised that they even assigned a number to it as the EVSE overhead power consumption of (my estimate) less than 10W is pretty insignificant when compared to the car's consumption. 10W/3kW = 0.3% (but this number can climb when less power is being drawn).
Level 1 is more inefficient than Level 2 for two reasons:
1. The car's overhead power consumption whenever charging is in progress
2. The very slight difference in the percentage that the voltage drop over the charger diodes is relative to the input voltage level of 120vac compared to 240vac.
For the i-MiEV, I had always assumed that the overhead power consumption is constant, as the cycling of our charger liquid cooling pump seems to be timed rather than controlled by a thermostat; however, this study used the Chevy Volt which has liquid battery heating/cooling as well and I would suspect that is controlled by various thermal sensors so it stands to reason there would be significant variation in charging kWh due to temperature.
All this brings me to discussing variations due to frequency of charging . I don't think this applies to the i-MiEV as long as we don't charge to 100%. What I'm saying is that charging our i-MiEV three times for an hour is the same as charging once for three hours, IF we stop short of going into the balancing portion at the end of charging.
Back to the OP's meier's original post -
The photo of the i-MiEV power consumption when charging shows 1981W. 1981W is too high for NA-standard 120vac. Assuming a maximum current draw by the i-MiEV OBC of 14A, this would mean a supply voltage of around 142 vac. If the voltage is 240vac, this would mean the EVSE is dialed down to a little over 8A.
Thus, repeating deemsh's question: what is the ac charging voltage?
Yes, Pout/Pin = 1400/1981 = 70.7% is rather poor. I, also, had never looked at this, and had assumed it was around 85%.
As a side note, in discussions with other EV owners we always want to distinguish vehicle energy consumption because many people don't understand the difference between EPA (wall-to-wheels) vs what's read on the dashboard of some cars, which is battery-to-wheels. In the case of my i-MiEV, I can say that over 8000 miles my i-MiEV wall-to-wheels was 4.2 miles/kWh. I need to go back to my notes and see what percentage of that is L1 vs. L2. Ref: http://myimiev.com/forum/viewtopic.php?f=28&t=403&start=20#p5744