I recently build my own a level 2 EV charger from an OpenEVSE kit. The heart of the charger is a big mechanical relay, which connects and disconnects the charging cable based on whether a car is connected. To control the relay, there is a small circuit board that communicates with the car, and also provides over-current, over-temperature, and GFCI monitoring. If any of these things go wrong, the relay will not close and the car will not charge.
The DC fast chargers include similar safety features, in addition to a big AC-DC converter. The DC power supply puts out several hundred amps at whatever voltage the car requests (usually 300V, but sometimes much higher). Normally, currents this high would require super thick & heavy cables, but DC fast chargers often avoid this using water cooling and active temperature monitoring in the cable. As the cable heats up from the excessive current, the charging equipment actively throttles the charging session to keep things from melting.
So yeah, there are a few mechanical things that can go wrong.
To deal with the high current on such relatively high (keyword here: relatively) gauge wire there's also massive active cooling involve. This adds even more to the complexity.
The DC fast chargers include similar safety features, in addition to a big AC-DC converter. The DC power supply puts out several hundred amps at whatever voltage the car requests (usually 300V, but sometimes much higher). Normally, currents this high would require super thick & heavy cables, but DC fast chargers often avoid this using water cooling and active temperature monitoring in the cable. As the cable heats up from the excessive current, the charging equipment actively throttles the charging session to keep things from melting.
So yeah, there are a few mechanical things that can go wrong.