DBMandrake wrote:You can measure the non-charging voltage at the cigarette lighter socket without putting the car in ready mode - just turn the key to ACC or ON without entering ready mode, and the cigarette lighter socket will have power without the DC-DC inverter running.
Good to know, and wow- that's a curious design decision. Likely a carryover from ICE design, but why stress the house battery by leaving the DC-DC converter off during accessory operation?
By "house battery" I assume you're referring to the 12v auxiliary battery ? (I've never heard it called that before...)
On these cars the DC-DC inverter that charges the 12v battery is outside of the main traction battery enclosure, so for it to operate the high voltage contactors in the pack have to be energised. This consumes power running the contactors, and also means that the high voltage system around the car is now live, as is all the electronics involved in driving like the drive inverter etc. Also the DC-DC inverter will consume some power even if the 12v battery is fully charged.
You wouldn't want this happening when the car is just set to ACC so you can sit in the car and listen to the radio, both from the safety reason of the whole high voltage system being energised unnecessarily, and also the power losses caused by having the contactors energised, the drive inverter powered up, and the DC-DC inverter running when it isn't needed.
(By the way the contactors are also energised and the DC-DC inverter active when the car is charging with the key off)
The battery is about 33Ah so you can use the radio for many hours without discharging the battery. In fact it takes quite a bit to run it down, which I found out the hard way recently. I have two heated seat covers that plug into the cigarette lighter socket - both of them turned on is about 50 watts or just over 4 amps.
While I was replacing the front brake discs I had the key in ACC so that the steering lock was disengaged so I could turn the steering back and forth. Unfortunately I forgot to turn off the heated seat covers...
The key was probably on for about 6 hours in total including a lunch break - by the time I tried to start the car the 12v battery was discharged enough that I could neither start it or Level 2 charge... I ended up having to connect a 12v battery charger to "jump start" it, and then plugged it into the Level 2 charger to charge up the main traction pack. (Which was at about 40% due to driving earlier in the day) As the main charging process charges the 12v battery as well I didn't need to leave the 12v charger on once the car itself was charging.
If the traction battery had already been nearly fully charged I would have had to just leave the 12v battery charger on to do the job as the car only charges the 12v battery until the traction battery has finished charging.
So running a high accessory load for a long time without the car in ready mode can potentially drain the 12v battery.