Possible Charging Automation

once the battery is full, the evse shuts off. so i suspect the 12v will still drain even if the wall power is off

 

My understading of the charge port is that when the EVSE is plugged in and the charging session has finished, is that the charging ECU and the battery ECU keep track of traction battery temps and if needed turns on the battery heaters. ( for the Gen 4 Prime the manual recommended not to keep the EVSE plugged in longer than 3 days ). I believe Gen 5 has a different / longer recommended time frame.

Similarly, in summer monitors traction pack temps while charging to turn on the A/C for battery cooling.

If heat is needed for the traction battery heaters ( while plugged in ) the charger in the car that the EVSE powers when plugged in will maintain the 12 volt battery as well as supplying the power for the heaters.
So, while leaving the EVSE plugged in, there may be a tiny drain of the 12 volt battery from those monitoring processes.
Keeping in mind, that both the Prius and Prime actually do automatic things at times like purging the EVAP system ( I think, funny unidentified noises have been reported here many times ) after the car has been off for several minutes or hours depending on if and when the ECU calls for something to be done.

In short the Prius and Prime are not supposed to overly strain the 12 volt unnecessarily.

Not many of us know the full scope of how each bit of 12 volt drain and recharge functions at any specific time, either while plugged-in, unplugged, in ACC, ON or READY even after comparing notes. And the specifics appear to keep changing with each Gen.

 

Page 81 in the manual:
●When the vehicle is left with the AC charging cable connected, the electricity consumption amount of the 12-volt battery increases due to controls, such as the system checking, operating. When the AC charging cable is not needed, remove it from the vehicle.

 

The battery drains all the time - it's just a question of how fast. Whether the drain caused by monitoring the charging port is remotely significant it would be somewhat interesting to measure. If only to put it in perspective - I suspect the amount of discussion about this drain is totally out of proportion to the amount of drain, if comparing against other system drains.

Think about what you've just said. How would it know there's no voltage on the charging port? It would have to monitor it. Which is the thing that's drawing the power.

There are multiple stages to determining ability to charge - step 1 is detecting whether the cable is physically connected. Step 2 is checking the voltage on the proximity pilot pin.

You minimise power drain by minimising the amount of activity, which you do by disconnecting the cable so it doesn't get to step 2 to start monitoring the proximity pilot pin.