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Comment by oceanplexian | Hacker News Reader

Level 2 chargers aren’t actually chargers, they just pass mains voltage and some signaling. The charger is inside the vehicle.

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Yes, just like your phone charger isn't a charger, yet I see absolutely no point in arguing about it, literally everyone understands what you mean when you call it a charger.

This pedantic ship has long sailed

The evse (misnamed charger here) needs to reduce the amperage based on what the car side wants. So it does more than just pass mains voltage.

That's not accurate. The EVSE communicates a max current to the vehicle, but does nothing to actively control the current. It should monitor the current and kill the circuit if the vehicle attempts to draw too much, but that only happens after the vehicle has misbehaved.

Correct. The control pilot signal from EVSE to EV is a PWM signal that indicates to the EV how much current is available.

It could drop at any time due to, for example, many chargers being connected to 1 circuit and the chargers coordinating with each-other to load-balance their connected vehicles (everyone gets their fair share), or it could be tied to solar PV generation so that charging doesn't import from the grid; the available current will change with how much excess PV is available, etc.

A well-engineered EVSE will notice when the EV is drawing more than the EVSE wants it to. It should then open the mains contactor at this point; cutting the EV's electricity supply. It will also hold the control pilot low to signal a fault to the EV.

This completely goes against my understanding of electricity. The correct amount of amps are pulled by the plugged in device, and it doesn't matter how much are available at the supply side (as long as it meets the minimum.)

Any good DC lab power supply can operate as a constant voltage source or constant current source. By default, the power supply will maintain a constant voltage at the terminals, but if the connected device starts too pull a current that's higher than the specified limit, the power supply will lower the voltage to keep the current in check.

Not saying this is the case here, of course, but they could do something similar that way if they wanted to...

These are not DC power supplies, thats whats inside the car, a boost DC power supply converting 240v AC to 400v or 800v DC, thats what regulates current and voltage to the batteries.

If the AC "charger" attempted to regulate current by varying voltage the actual onboard charger would just attempt to pull more current to make up for the voltage drop and probably trip the whole thing.

There would be no point in regulating the AC current, it would make the charger very complicated and expensive replicating much of whats in the DC converter/charger in the car.

A full DC charger like at a charging station does do this because it is the actual charger bypassing the cars small internal DC charger with DC leads going directly to battery at full pack voltage.

Yes, this goes against my understanding as well. I don't think the laws of physics changed that much in the last few years, but I could be wrong.

Sorry, I was wrong about this. Too late for me to edit my original posting.

Got a reference for that? As far as I know (as the linked article says), the EVSE doesn't do anything to control the current other than telling the car how much it can draw.

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