Home Charging Question

[SDRick]

Apparently it is recommended that a plugged in Tesla is a happily Tesla. Do I take that to mean that while the car is plugged in, any power being consumed by the car is running off the household current rather than the batteries?

Or does this occur only while the car is actually charging and not just plugged in?

 

[Boatguy]

I think the answer is somewhere in between.

The car always runs off the batteries, but at some point the vampire drain will lower the SOC enough to trigger a charging cycle. However, I've noticed that even though my car is set to only charge at night, if a door is open, which then turns on the HVAC, displays, etc., the car starts immediately drawing from the HPWC.

 

[mikeash]

When the car is just sitting, it draws no power from the wall. Some of the computers remain alive by draining the 12V battery. When the 12V battery gets low, the car recharges it from the main battery. Every two days or so, the car will top off the main battery from wall power.

If climate control comes on (either because you activated it with the app, or you opened a door) then that will draw from the wall when you're plugged in. This means you can preheat or precool your car without touching the battery, which is pretty nice.

I'd also guess that the battery temperature control might use wall power and be more aggressive when plugged in, but I don't know about those things in enough detail to say.

 

[SDRick]

Wouldn't it make the most sense that at a minimum, while the car is plugged in, any power use will either come from the wall (or at least trickle charge the battery maintaining battery's current SOC?

 

[miimura]

Wouldn't it make the most sense that at a minimum, while the car is plugged in, any power use will either come from the wall (or at least trickle charge the battery maintaining battery's current SOC?

The efficiency to do that is too low. You would take a lot more power from the wall than the current strategy. The only thing that might make sense is for Tesla to employ a direct 12V charger from the charging inlet, without involving the traction battery. However, depending on the EVSE, the 12V charging power and the power to keep the contactor closed, may be similar, again leading to poor efficiency.

 

[rfmurphy81]

I've had cases where I've plugged into my garage outlet and, even with the climate turned off and scheduled charging set to overnight, the charge port lights up green. I don't remember if it was solid green or flashing, as I haven't looked out for it in a while. It seems to do this for a few moments before turning a solid blue color, which I assume it stays that way until the scheduled charge time. Could there be other scenarios when the car would draw power from the wall when not actively charging or running the climate? Does solid green mean something different from the usual blinking green?

 

[DCGOO]

Wouldn't it make the most sense that at a minimum, while the car is plugged in, any power use will either come from the wall (or at least trickle charge the battery maintaining battery's current SOC?

That is essentially correct. When the car is plugged in, but not actively charging. HVAC and other non-charging loads are covered by the shore power connection. Out here where it gets cold, that is particularly important in the winter when you want to warm up the cabin before you jump in a -15ºC car and head to the office. Plugged in to shore power is the source for that.

The main batteries have to lose around 5% before the chargers begin to refill the batteries. In my case that happens roughly every 3 days or so if the car is not being used.

Unless I know for sure that I am leaving again within a few hours, I plug in.

 

[jerry33]

I've had cases where I've plugged into my garage outlet and, even with the climate turned off and scheduled charging set to overnight, the charge port lights up green. I don't remember if it was solid green or flashing, as I haven't looked out for it in a while. It seems to do this for a few moments before turning a solid blue color, which I assume it stays that way until the scheduled charge time. Could there be other scenarios when the car would draw power from the wall when not actively charging or running the climate? Does solid green mean something different from the usual blinking green?

Dark blue means the car is waiting for the time you've set for it to charge.
Solid green means it will charge if necessary and it's within the time you've set (That's anytime within six hours from the time you've set).
Blinking green means actively charging.
Red and yellow are error colours.
Light blue is the charge port is ready to accept the cable or it's okay to remove the cable.

The car draws power from the wall when pre-conditioning or charging.

The car wakes up periodically to check the state of the 12V battery. If the 12V battery need power, it takes it from the battery. The battery may or may not charge from the wall at this time depending upon the SOC of the battery and the time you've set for charging.