That's not how battery chargers work. They don't rely on Ohms law, because that would be very wasteful of energy. In constant current mode, the voltage is allowed to adjust to maintain the current. What sets the voltage? The battery.
Correct. The battery does in the sense that the charging station, in order to supply the requested constant current, would need to be operating at a voltage above the pack voltage such that current flows from the charging station to the battery, following Ohm's Law considering the resistance of the connector, cable, and any internal resistance of the battery & other components in the circuit between the power supply and the battery.
I didn't say it "relied" on Ohm's Law (and I don't even know what that means). But it certainly has to follow it!
The voltage at the charger and the voltage at the battery are two different measurements, and will differ by unknown amounts, because of the uncontrolled variables in the cables and connections. Even in much lower power equipment supplies use dedicated wires to sense the voltage on the load to deal with these problems. I don't believe the Tesla cable has such remote sense wires, it would take two. It's called a Kelvin connection.
Yes, this is true, and I agree that they are not worried about the small amount of I^2/R power drop over the connector (or perhaps it's accounted for by overshooting the requested voltage by an amount equivalent to the predicted IR drop of the cable/connector). I don't think this is really germane to what we are talking about anyway. This would only be important with test equipment and ultra sensitive devices where a precise voltage is required at the component in question.
I don't think that is correct. A small delta in the measured voltage (such as voltage drops in the cable) will result in large variations in the current. So even in constant voltage mode, there needs to be local voltage sensing and so local control.
Yeah, the current varies...So what? This is exactly why the charge rate (current) tapers off at higher SOC. All that is happening here is that the car's BMS says, for example, I need 415V constant voltage. So the charging station outputs 415V (or as I said above, maybe it overshoots to account for IR drop in the cable/connector). At the point where the BMS switches from CC to CV, maybe the pack is at 360V and current is rushing in, but as the pack charges and the voltage rises to 370, 380, 390, 400V, the current tapers off because why? Ohm's Law. I = V/R, where V is actually ∆V, the difference between the output voltage of the charging station and the internal voltage of the battery. With a fixed R, as the pack voltage approaches the charger's output voltage (∆V -> 0), I will similarly drop. Once I gets to a certain set low point, the BMS declares charging complete and terminates the charging session, shutting down the charging station.
Sure, as you said, there is going to be a difference in the voltage at the output of the DC/DC converter in the charging station and the input of the battery in the car, but if this is significant at all, it's probably easy enough for either the charging station or BMS to compensate for it (the charging station knows what the R between the converter and the connector is, so can overshoot V to account for it, and the BMS similarly knows what the R between the charge port and the battery pack is, so can request a slightly higher V to account for that. And if it decides it needs to get really precise, it can simply request more V from the charging station such that the V it sees at the positive electrode of the battery pack is what it wants.
I think you are mixing the AC input with the DC input. It's not just a matter of power, the two circuits are different.
No, just pointing out that the car already has a DC/DC converter in it for AC charging. You made the statement that a buck/boost converter would contain expensive components, and while the automotive grade 11kW components are probably not cheap, the point is they are already in the car.
Yes, a buck is a different topology than a boost or buck/boost. The point is the charger is not in the Supercharger. That is just a power supply, like the wall wart charging your phone.
Actually, the first Superchargers literally were made of 8 Model S on board chargers ganged together for additional current capacity (and able to be allocated as needed to each of the two paired pedestals). So yes, the charger IS the same as the Supercharger! I think this fact is an overlooked reason for the success of Superchargers: Tesla constructed them out of proven, high volume components that made them reliable and really cheap to construct (as opposed to third-party DC fastchargers who were (are!) dealing with unproven designs made in very low volumes.
I would love to see a spec of the charging cable interface. But that's not happening any time soon, no?
The hardware? As you're aware, Tesla is opening up the NACS standard, so a lot of the hardware specs are available (or being made available).
As for the Supercharger protocol itself, I don't know that the spec is publicly available (or will be). But again, in general, it's not much more complicated than BMS requests a set current until it reaches a set pack voltage threshold, and then it switches over the CV and requests a specific voltage until the current being delivered drops below a set amount. Sure, there are several details such as whether it's compensating for IR drop and what not, but it's not conceptually any more difficult than that. The more interesting communications taking place across the connector would be things like vehicle authentication (for billing purposes, etc.)
