Differences in EV charger tech other than plug shape.


Seems like it should be as simple as converting AC to DC., passing on all available voltage (up to a safe limit) to the car, and stopping it when the batteries are full.

Similar to what a wall brick does for your devices on a smaller scale, though the brains are in the device not the wall brick. Why isn’t that done with cars?

I see mention of ‘different technologies’, and ‘better chargers vs lesser chargers’, etc. and I feel like there must be more to it.

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It’s a question of where the AC is converted to DC. At home, this is done by tech inside the car, so you just need to give it AC from the wall. The final speed/efficiency will depend on how much voltage you can make available. A typical wall outlet will charge the car slowly. The type of outlet you use for an electric dryer or stove will charge about twice as fast. Both of these charging levels take hours to fill an EV because the voltage is capped at household levels and the onboard conversion hardware sacrifices efficiency for versatility/portability.

The gas station-style charging stations out in the world use “DC fast” charging. They have their own converters that accept much higher voltages and are generally more efficient. They then deliver DC directly to the car, bypassing the onboard convertor.

DC fast charging is, as its name implies, much faster and hence suitable for a “fill-up” on a long road trip or in exceptional circumstances. However, it would be overkill to install tech like that in homes. Normal overnight charging from a wall outlet is usually enough to fill up a car, or at least offset the day’s usage.

Since every car is a bit different, the AC->DC power conversion happens inside the car itself so that it’s up to the car’s needs, and the plug’s job is mainly to tell the car what it’s allowed to take. Level 1 chargers will give it low limits, level 2 chargers will give it much higher limits (and typically higher voltages). In your home, the “charger” is usually little more than a direct AC power connection to the plug, and some basic intelligence to do this communication with the car. It keeps the external equipment simple, and the car can carry as big a converter as it wants and take advantage of whatever the car has, like cooling.

Level 3 chargers usually do get direct battery access, but in order to do this the car must tell the charger what its voltage is and the charger must be capable of providing that voltage. If all is well, some crazy amounts of power can be delivered by a big external AC->DC converter. Also the car must have the extra connectors that give direct battery access for this to even be possible, so these fast chargers are only compatible with cars that have the plug on their side.

Most tech, even with plug shape variances, meet these general criteria, and simple plug adaptors do exist which require no power to function.

You have AC charging and DC charging.

For AC charging, nothing special is needed. It is designed to be compatible with the normal electricity grid.
Charging your car is basically connecting an extention cord to the car.
The battery charger is built into the car itself and will convert the AC to DC the battery needs.
This compatibility limits the amount of power you have available and how fast you can charge your car. It is often limited to 7.6kW or 11.1kW, still suitable for home charging during the night.

On the go you want to charge fast. There we use DC charging.
The charger is external to the car and provides DC power, often 100s of kW.
Most of the time, the battery is the limiting factor and the maximum charging rate can only be maintained for 10-20 minutes in ideal circumstances.

Conceptually, it is very simple, but what makes it less trivial is the safety requirements as you are dealing with a lot of power.
Besides pure charging, there is also communication ongoing between car and charger to exchange charge status information and even automatic billing, etc…