Understanding how DCQC works without having a firm understanding of basic power electronics and switching power supplies will always get you a bunch of incongruities and confusion, as any simplified layman model of the components required for a DCQC+electric car system will have essential components removed for clarity. Add in more confusing concepts like requesting a voltage vs current and there will be no end to the discussion.
Charging any battery as quickly as possible is done through a constant-current-then-constant-voltage process, where the current into the battery is limited to some maximum amount until the per-cell voltage reaches - in the old Leaf - 4.08V, and then the charger will effectively become a constant voltage supply at that voltage, with the battery drawing whatever current it does at that particular voltage.
There is no such thing as a perfect current source or a perfect voltage source, and as such any power supply, including a DCQC station, will always be both in some way. Likewise, batteries are not just voltage sources - they have internal resistance and they heat up during use, so there are additional requirements to safely charging and discharging. The battery cannot willy nilly ask for any amount of current and receive it, nor can the DCQC just supply any amount of current without regard for voltage and temperature. These are parameters that must be communicated back and forth, and these are exactly the kinds of things you see running over the CHAdeMO CAN-bus.
Additionally, there are no voltage sense wires going over the CHAdeMO protocol, so the charger has no direct way of knowing what the actual battery voltage is, without the resistance of all the wires going to it. It's charging blindly on CAN-messages, essentially.
Taking all of this into account, pretty much the only way to ever design a DCQC station is to first let the station voltage-match to the battery, and then increase the supply voltage stepwise up to the point where either the maximum battery voltage (4.08V/cell, approx. 390V in the Leaf) is reached, or until the battery says it can't take any more. Anything else on the HV bus will simply be along for the ride at that point, drawing whatever current it draws at that amount of overvoltage. This is how the extender is charged, and how ANY car with CHAdeMO or CCS will be able to add in an extender and have it quick-charge effortlessly.
This is exactly what I see happening in my car. Near empty, I charged at a CHAdeMO station. The station supplied approx. 110A to the car, of which 80 was going into the extender and 30 into the main battery.
Charging any battery as quickly as possible is done through a constant-current-then-constant-voltage process, where the current into the battery is limited to some maximum amount until the per-cell voltage reaches - in the old Leaf - 4.08V, and then the charger will effectively become a constant voltage supply at that voltage, with the battery drawing whatever current it does at that particular voltage.
There is no such thing as a perfect current source or a perfect voltage source, and as such any power supply, including a DCQC station, will always be both in some way. Likewise, batteries are not just voltage sources - they have internal resistance and they heat up during use, so there are additional requirements to safely charging and discharging. The battery cannot willy nilly ask for any amount of current and receive it, nor can the DCQC just supply any amount of current without regard for voltage and temperature. These are parameters that must be communicated back and forth, and these are exactly the kinds of things you see running over the CHAdeMO CAN-bus.
Additionally, there are no voltage sense wires going over the CHAdeMO protocol, so the charger has no direct way of knowing what the actual battery voltage is, without the resistance of all the wires going to it. It's charging blindly on CAN-messages, essentially.
Taking all of this into account, pretty much the only way to ever design a DCQC station is to first let the station voltage-match to the battery, and then increase the supply voltage stepwise up to the point where either the maximum battery voltage (4.08V/cell, approx. 390V in the Leaf) is reached, or until the battery says it can't take any more. Anything else on the HV bus will simply be along for the ride at that point, drawing whatever current it draws at that amount of overvoltage. This is how the extender is charged, and how ANY car with CHAdeMO or CCS will be able to add in an extender and have it quick-charge effortlessly.
This is exactly what I see happening in my car. Near empty, I charged at a CHAdeMO station. The station supplied approx. 110A to the car, of which 80 was going into the extender and 30 into the main battery.
