ROBERT via EV wrote: > Roger, let me try to clarify my concern. A person buys a third party > J1772 to NEMA adapter (made in China and made cheap). The adapter has a > NEMA rated 20A plug. The adapter does not produce a modified pilot > signal.
Just to be clear, the adapter does not (*cannot*) produce a modified pilot signal since the NEMA outlet has no provision for a pilot signal connection and the charger that plugs into the NEMA outlet does not require a pilot signal. The pilot signal *from* the J1772 EVSE is one-way only; that is, it is generated by the EVSE to inform the load of the maximum current that may be drawn *at that particular time* (i.e. while the EVSE may be capable of up to 50A, it is possible for it to limit the current available to the load to any value less than this at any time). There is no way for a J1772 charger or adapter connected to the EVSE to tell the EVSE to reduce the maximum available current. > I take the cord and plug from the EVSE that is rated at 50A and > plug into the adapter. I take the 20A coil and plug from the charger in > my converted car and plug into the adapter. The charger will not draw > more than 20A from the EVSE. This is OK load wise because the EVSE can > output 50A. However, it is an unsafe circuit. I have connected a 50A > rated source to a 20A circuit with no interconnecting protection > device. I understand your concern with this configuration now. I agree that the EVSE breaker will not provide adequate protection for a lower current rated J1772-to-NEMA adapter connected between the EVSE and the load (charger). Note that this scenario is irrelevant in the situation where a NEMA outlet is provided at each parking spot as the charging infrastructure (which is what was proposed). Note also that any charger with any safety agency (CSA, UL, etc.) listing *will* have a protection device at its input appropriately rated to protect it. In this case the safety concern reduces to a user who tries to use an adapter that is under-rated for their charger (but still does not apply to the situation of a NEMA outlet charging infrastructure). > Lets go the other direction. I have a NEMA to J1772 adapter > with no pilot signal. This situation is *not* possible. The reason you have a NEMA to J1772 adapter is to provide a J1772 connection to the charger, and the J1772 charger *requires* a pilot signal from the EVSE ("adapter", in this case). The adapter *must* provide a pilot signal, the only question is if it provides a pilot signal that is appropriate for the rating of the NEMA outlet/circuit that it is plugged into. > If the cable from the adapter is plugged into a car > with a 50A charger, the circuit breaker will trip No. Since the J1772 charger requires a pilot signal, and the EVSE/adapter must provide one, the 50A rated charger will draw no more than the amount of current signalled by the pilot signal. In the absence of a pilot signal, the charger will not draw *any* current. The only safety concern when using a NEMA to J1772 adapter is that the adapter might generate a pilot signal that allows the charger to draw more current than the NEMA outlet/circuit it is plugged into is rated for. This should not occur for any competently designed adapter. As I described in my prior post, if a 120V NEMA to J1772 opportunity charge cord (adapter) has a 5-15P NEMA plug at the wall end, then it "knows" that no matter what the supply circuit it is powered from might be rated for (i.e. 15A or 20A), it cannot allow the load to draw more than 12A since its own connector is only rated for 15A (and such a circuit is limited to 12A max continuous loading). If it has a 5-20P NEMA plug at the wall end, then it "knows" that it can allow the load to draw up to 16A since its connector (and wiring) are rated for 20A and it can only be plugged into a receptacle/circuit rated for 20A. In the event of use of an incompetently or unsafely designed adapter that generates a pilot signal allowing the charger to draw more current than the NEMA outlet it is powered from can safely deliver, the protection device between the supply and the NEMA outlet will trip and safely protect all connected devices. I think that there is actually very little safety concern with a NEMA outlet charging infrastructure since the vast majority of people using NEMA to J1772 adapters will be owners of OEM EVs and using the OEM opportunity charge cord provided by the OEM (i.e. competently designed adapters). The main advantage of the NEMA outlet infrastructure, IMO, is that there are no charge cords left at each parking stall to be vandalised or stolen, however, the big disadvantage is that the vast majority (is anybody still building conversions?) of EVs that will use the charging infrastructure *don't* have NEMA connectors, but rather J1772 charge inlets. So, each EV must carry around a NEMA to J1772 opportunity charge cord/adapter to plug in and must somehow secure this relatively expensive cord so that it is not stolen while the car is unattended. I think it would be relatively difficult to get support for installation of a new NEMA outlet-based charging infrastructure, and that there is probably an opportunity here for an inexpensive *level 1* J1772 charging station that could be installed in place of each NEMA outlet. Ideally, someone would come up with an EVSE that does not have a permanently attached J1772 charge cord, but instead allows (requires) the user to first connect their own charge cord to the (de-energised) EVSE, and then plug the J1772 paddle into the vehicle receptacle. A possibility is for the EVSE to have a receptacle into which the user's cord plugs that is equipped with a secure cover that can be closed to prevent the user's cord from being unplugged. Provide an interlock such that the receptacle is de-energised when the cover is open, and a solenoid or other securing mechanism that prevents the cover from being opened after the J1772 paddle is mated to the vehicle receptacle and is energised by the EVSE. Cheers, Roger. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)