This looks interesting, especially if one relies on public charging a lot. I'd be interested to hear feedback from the electrical safety experts about this. I'm also interested in how the gadget spoofs the J1772 control signal -- how can it tell whether you are drawing 30A, 40A, 70A, or 80A? Or is this just a non-issue?
PROXIMITY PIN
The Modular EV J1772 to NEMA 14-50 adaptor spoofs the car side of the protocol with a 2.7k +/-5% resistor from the proximity pin to ground. For some reason, they decided to put 6" - 8" of blue wire with the proximity pin inside the box that should have had an insulated twist wire nut on it; the yellow wire nut was not installed, but was just bouncing around in the box!
PILOT SIGNAL PIN
The EVSE generates the pilot signal through the pilot signal which obviously also goes nowhere since this all terminates in a NEMA 14-50.
From the car side of the proximity pin side, there is switch (S1) that connects the proximity pin to ground through the 1.3k resistor (I physically can't see it since it is epoxied in). In addition, there is another 2.7k resistor in parrallel that normally goes from the pilot pin to ground. finally, there is a diode.
When S1 is open, only the 2.7k resistor is connected to ground. When this switch is closed, the combined resistance (1k * 2.7k) / (2.7k + 1.3k) should be 880 ohms, which tells the onboard charger to pull current in State C.
State A = not connected, +12 volts DC
State B = ready and connected, 2.7k car side resistance, 1kHz square wave +9/-12 volts with pulse width determining how many amps the EVSE has available
State C = charging, switch S1/S3 (depending on which diagram you're looking at) is open on car, 1.3k resistor added in parallel to 2.7k resistor, 880 ohms overall, +6/-12 volts
State D = ventilation for lead acid batteries!!!! The Modular EV adaptor obviously has no logic to send this signal
State E = error, 3 / -12 volts, which this unit can't send either
State F = ???, 0 / -12 volts, can't do it either
So, you could pull as many amps as you want, right up until you smoke something, or the circuit breaker pops. Hopefully, most folks will respect that most public J1772's are 30 amp only, and not pull more than that just because the pilot signal isn't protecting the EVSE and power circuit.
http://code.google.com/p/open-evse/wiki/J1772Basics
