> Background: The "official" CCS does not provide the possibility to draw energy out of the car. This is in contrast to the CHAdeMO, which prepared this topic from the beginning.
Incorrect, and there is no need for this hackery. V2G over CCS2 was standardised in ISO 15118-20 for example when the OP wrote this, and a lot of cars will happily allow bidirectional power transfer (taking energy out) using the proper command.
The difference is, using the proper BPT method is designed to do this without damaging or bricking the battery and adds the necessary protections ie the car will disable BPT once the battery begins to run too flat to support it, and it will send the external device a power limit which it must follow.
Virtually all battery protections are disabled during pre-charge (the hack OP is using) to the point where you can probably run individual cells to 0V and then you’ll need to throw out your car. That’s why the well thought-out models (Tesla, Hyundai) don’t allow pre-charge for very long (seconds or minutes) whereas the MG, with its buggy and poorly-designed software, had no time limit.
* Why are battery protections turned off during precharge? *
Suppose you actually ran your battery down to real 0% and then let it sit, turned it on, ran it again until it stopped — and so on, until your battery actually has zero energy left and the cells are on the verge of falling to 0V. At this point, the discharge current limit is 0A, so if you draw 1mA from the battery the car will trigger an emergency shutdown and everything will turn off.
Unfourtunately to connect to a charger requires a little bit of random current flowing in both directions to equalise the voltage level between the car and the charger. Protections are momentarily disabled, normally for only around 500ms which is about how long precharge takes, so that the car will let you connect and begin charging when the battery level is below 0%. Otherwise, the vehicle would be bricked if you ran it too low, since the car would emergency shutdown each time you try to charge it.
jamesy0ung · 18m ago
This is the type of content I come to HN for. Thanks for the insights.
Incorrect, and there is no need for this hackery. V2G over CCS2 was standardised in ISO 15118-20 for example when the OP wrote this, and a lot of cars will happily allow bidirectional power transfer (taking energy out) using the proper command.
The difference is, using the proper BPT method is designed to do this without damaging or bricking the battery and adds the necessary protections ie the car will disable BPT once the battery begins to run too flat to support it, and it will send the external device a power limit which it must follow.
Virtually all battery protections are disabled during pre-charge (the hack OP is using) to the point where you can probably run individual cells to 0V and then you’ll need to throw out your car. That’s why the well thought-out models (Tesla, Hyundai) don’t allow pre-charge for very long (seconds or minutes) whereas the MG, with its buggy and poorly-designed software, had no time limit.
* Why are battery protections turned off during precharge? *
Suppose you actually ran your battery down to real 0% and then let it sit, turned it on, ran it again until it stopped — and so on, until your battery actually has zero energy left and the cells are on the verge of falling to 0V. At this point, the discharge current limit is 0A, so if you draw 1mA from the battery the car will trigger an emergency shutdown and everything will turn off.
Unfourtunately to connect to a charger requires a little bit of random current flowing in both directions to equalise the voltage level between the car and the charger. Protections are momentarily disabled, normally for only around 500ms which is about how long precharge takes, so that the car will let you connect and begin charging when the battery level is below 0%. Otherwise, the vehicle would be bricked if you ran it too low, since the car would emergency shutdown each time you try to charge it.