Automatic charge connection testing?

[ka9q]

I've noticed, as many of you probably have, that when you first connect an EVSE to a Tesla with charging scheduled at a later time, the Tesla still asserts READY and ramps up to a few amps. Then it drops READY to de-energize the cable and waits for the scheduled charging time. The whole process takes maybe 30 seconds.

I hypothesize that this is to test the integrity of the connection between the car and charging cable. It's best to detect a bad connection right away so you can fix it before you go to bed and wake up with an uncharged car. If the connection between EVSE cable and car is solid, the voltage shouldn't drop much under a small load. If the voltage drops significantly, something is wrong. Flash the red light on the charge port, put a message on the dash and refuse to charge.

Even when charging is not delayed, the load is often ramped up slowly to the maximum setting (e.g. 30A, 32A or 48A). Again, this is probably to test the integrity of the EVSE/car connection, avoiding a nasty situation if it's not tight.

What do people think?

 

[widodh]

Sounds logical. You want to make sure that the car can actually charge. Better to test that right away then not charging the car in the night.

 

[ka9q]

Actually, this could explain the power ramping we also sometimes see during supercharging. Some pretty heavy and potentially damaging currents flow through that connector and port, and by varying them you can measure the voltage drop at different current levels. Communication between charger and car is a bit more sophisticated during DC supercharging so there are probably other ways to measure voltage drop, though.

 

[ewoodrick]

We are generally talking about really large currents here. They are pretty dangerous and never have consumers had common access to them.
Yes, the initial handshake is to determine integrity and if there is any ground leakage. Better option than killing people.
Ramp ups are for the equipment, to reduce transient currents. Also to keep voltage levels stable. A 30A immediate hit on residential service cause lights and more to blink.

Generally the transient currents are also nasty, for a 39A circuit they can be hundreds of amps