I have a 2015 model S with dual chargers and a HPWC on a 100 amp circuit so I can (and do) charge at 80 watts. When I first plug the charger in it reports 242V and the voltage slowly drops as it ramps up to 80 watts. At that point the voltage has dropped to 235. If my (house) air conditioner starts up while the car is charging it can get down to 233V. Is this acceptable or something that in should be concerned about?