I am also an engineer, so I feel qualified to add my voice to the technical discussion.
A few things to point out:
[*]This modification, if performed as specified, does not apply 240v power to any component not rated for it.
[*]The extra 120v is flowing through a separate, fully insulated conductor.
[*]The loss of the FDCD/thermistor is real, but the risk can be fully mitigated by the use of properly rated connectors. More on this below.
[*]No additional current is flowing than in the original design- 12 amps both ways. Therefore, no more heat can be produced.
[*]This modification is intended to be carried out by technically savvy persons, able to assess the inherent risk of doing so.
On the FDCD/thermistor: I believe this is indeed a thermistor. Measuring the heat of the connector is a bright idea on EVSEs which operate at(not beyond) the limit of the design and code. Especially true with flaky, old, or corroded outlets out there. I've warmed up some connectors pretty hot myself. However, please consider this- this modification replaces the original connector, rated for 15A, with a new one rated for 30A. This instantly mitigates any risk of operating without temperature feedback, because the connector is no longer being operated anywhere near its limit- half, in fact. Furthermore, many other EVSE designers saw fit to leave a temperature measurement device out entirely, even with a plug being used at its limit. Based on these facts, I see no risk at all in bypassing the FDCD/thermistor when a higher-capacity connector is used. Notably, if you were going to use a 15A connector, you'd just going to be leaving the original, FDCD/thermistor-equipped one on there- so it's a wash anyway. Even if operated with a 15A connector without a temperature measurement device, the risk is no more than Fiat owners take every day with their non-protected EVSE plugs.
On the heat question: This modification works because of two equations: P=V*I, or power is voltage multiplied by current. The EVSE tells the car to draw the same current before and after the mod. So previously, 120v*12A=1440W of charging power available. After the modification, it becomes 240*12A=2880W, so double. The power flowing through the wire is double, but the power dissipated as heat in the wire does not double. Why? That is the second equation for finding power: P=I^2*R, or power is resistance times current squared. Voltage isn't in that equation at all- I could run 12A through a wire a 12V, 120V, or 1200v and the wire would heat up the same amount. The resistance of the wire remains constant unless it is damaged in some way.
Regarding "pushing" outlets near their max power- a standard NEMA 5-15 outlet is rated for 15A. EVSEs draw only 12A because the National Electric Code states that plugs, connectors, and receptacles should be used at their maximum power only intermittently, not constantly. When in constant use, the maximum allowed is 80% of the nominal maximum, or 12A in the case of a 15A outlet. 12A is already a reduced rate for safety, and if the connector is in serviceable condition it will do fine with a 12A constant load. If it is faulty, there is a real risk, but that goes for any piece of equipment. Don't plug your EV into suspect outlets.
Bottom line: I believe that this modification is safe when carried out by qualified persons. You know who you are. If in doubt, spend the dough on EVSEupgrade.
Last edited by nedfunnell
on Wed Oct 08, 2014 5:25 pm, edited 1 time in total.