Interressant stukje over het eigenlijke laadproces hier:
https://www.quora.com/How-does-the-Tesla-Supercharger-work
En omdat niet iedereen een account daar heeft, copy/pasta:
Tesla Superchargers are what are known as DC quick chargers. Basically the idea is that it supplies DC (Direct Current) (as opposed to AC — Alternating Current) directly to the car’s battery. AC chargers (like the one you might have at home, take AC current directly from the grid, where it must be converted to DC using a rectifier circuit (the actual charger) inside the car. This is very similar to the wall wart power supply found in all kinds of electronics, but on a bigger scale. The problem is that the rectifier (also called AC/DC converter) circuit is limited in how much power it can transfer, so charging rates are limited to around 10–20kW.
By bypassing the AC/DC converter, higher power rates can be achieved. Of course the converter still exists, in the Supercharger itself, but it’s more economical to build a relatively few massive AC/DC converters capable of delivering 100kW or more and putting them in stationary Superchargers than putting that all that heavy equipment (and the cooling it requires) on board the vehicle.
That is the reasoning behind DC quick chargers and why they can deliver more power. But how do they work?
Most rechargeable batteries charge similarly, and all DC quick chargers, whether they be Tesla Superchargers or CHAdeMO or CCS quick chargers. Basically when the battery is at a low state of charge, the battery management system (BMS) calls for a given constant current (CC) to be fed into the battery. For example, it may call for 300A of current, which the Supercharger would supply. The voltage of the circuit will be dependent on the state of charge of the battery. This may be 350V when the charge commences, and be closer to 400V when the battery is full. But during this phase of charging, the Supercharger will deliver its constant 300A of current which charges the battery.
Note that a BMS may request a certain amount of current, but the actual charger might not be able to deliver that requested amount. That may be because the charger is simply not powerful enough, or there is some kind of environmental condition such as the unit is overheating and needs to throttle itself back. This is fine, the charger will simply give what it can and the car will charge slower as a result.
Once the battery pack voltage crosses a certain threshold, meaning it has achieved a set state of charge, the BMS will command the Supercharger to switch to Constant Voltage (CV) mode. Each type of vehicle will have a different threshold at which this happens. In Teslas, I believe it is about 50% state of charge. In Nissan LEAFs, it’s more around 80%.
In Constant Voltage mode, the charger outputs a set voltage which is slightly above the battery’s 100% full voltage. This causes an amount of current to flow into the battery that continues to fill the battery, and the battery voltage will continue to rise. As it gets closer to the CV voltage, less and less current flows, meaning less power is being delivered, i.e., the charging rate tapers off. This is why it is very fast to charge an EV from empty to 75–80%, but the last 10–20% takes a lot longer.
Note that Teslas start to taper off at a pretty low state of charge. So even though a Supercharger is capable of delivering 120kW to an individual vehicle, because the vehicle has switched over to CV mode, it will be drawing less than the max for a significant portion of the charging session. For this reason, Tesla designed Superchargers to work in pairs. Each pair has a drive unit that is capable of delivering 145kW total, split between the pair. If two vehicles at low state of charge both plug in to the pair at the same time, they will each only receive about 72.5kW each. But it’s more likely that one vehicle will be nearing the end of its charge and only drawing 30–40kW or so, so the other vehicle will be able to draw 95–105kW. If you arrive at a Supercharger with 8 stalls, they will be numbered 1A, 1B, 2A, 2B, 3A, 3B and 4A, 4B. The A/B designations are the pairs. So if someone is plugged into 3A, but both 1A and 1B are empty, you will usually want to plug into 1A or 1B and not 3B. But if you cannot find a completely empty pair, you will want to find a car that is nearing the end of its charge to pair up with. This architecture allows Tesla to save money on Superchargers by only having to have half the expensive drive circuitry as there are stalls, while still being able to offer a large number of stalls for redundancy or busy Supercharger sites, and without significantly impacting users’ charge rates.
