Limiting Charging Amps

[Sius]

I am actually looking at my JuiceNet app as my wife's 2022 RWD is preconditioning for her drive to work. Climate control is set to 76 F in our 46 F garage. It was fully charged when it started preconditioning and the current draw from the charger is anywhere from 12 to 20.1 amps. The app just told me that "Your car cabin is now..." and it is drawing between 10.6 and 12 amps while it waits on her. Hope this helps!

 

[Sophias_dad]

The car can only use external power when commanded to start charging; it has no programing to do otherwise.

That's a false statement, since when I pressed the 'stop charging' button, then turned HVAC off and on it started using external power again without me commanding 'start charging'

 

[brkaus]

That's a false statement, since when I pressed the 'stop charging' button, then turned HVAC off and on it started using external power again without me commanding 'start charging'

Lots of design choices, but I *think* this is what I would expect if you look at the individual pieces.

If you’re standing by the car and want to stop the power to disconnect you may hit stop charging and expect all the power to stop. You hop in the car and go.

If you wake up in the morning and turn on the pre-heat you would expect it to pull from the wall.

Of course they could have added more states and or more buttons. But the likely decided most that “stopped charging” would be unplugging and that was the simple way.

 

[Sophias_dad]

I had omitted it, but during my first testing the battery in my meter was running low and consequently reading higher-than-correct amperages(5.5 vs 5 amps). That was corrected by my second post regarding the draw of the HVAC.

 

[DuncanM]

That's a false statement, since when I pressed the 'stop charging' button, then turned HVAC off and on it started using external power again without me commanding 'start charging'

Yes, I misspoke. This is from the M3 Owner's Manual:

Note
Whenever Model 3 is plugged in but not actively charging, it draws energy from the wall outlet instead of using energy stored in the Battery. For example, if you are sitting in Model 3 and using the touchscreen while parked and plugged in, Model 3 draws energy from the wall outlet instead of the Battery.

 

[rrolsbe]

Ok, so the results are in.. Stacy's Mom(my 2018 AWD 3) will take around 30 amps(7+kw) continuously during cabin heating. Its a wee bit above that initially, but settles down quickly, and ramps down further as the cabin warms up.

As I stated before, turning down the current(in the car) to 5 amps means it will take no more than 5 amps no matter what sequence is used or what is turned on or off.

Interestingly... if the car is charging and the HVAC is turned on, and then you command the car to stop charging, The drawn power goes to 0 and all HVAC keeps running but its power is drawn from the battery. If you then turn HVAC off and back on, it reconnects to the HPWC power and draws whatever it needs(up to the limit set in the car).

Thanks for your post. In your last sentence of your post, does the HV battery supply the remaining energy (if required) over and above what is provided from the wall? For my use case, using energy exclusively from the wall and NO energy from the HV traction battery would normally be my first choice.

Regards

 

[davewill]

Thanks for your post. In your last sentence of your post, does the HV battery supply the remaining energy (if required) over and above what is provided from the wall? For my use case, using energy exclusively from the wall and NO energy from the HV traction battery would normally be my first choice.

Regards

The best way to understand it is that there really isn't a such thing as "using energy exclusively from the wall". When the charging system is active, the output of the on-board charger is connected to the HV battery and to the rest of the car. Anything that draws power is drawing it from that connected system. In the case where the car is actively charging the battery, the result is what you describe, if the car draws less power than the wall is providing, nothing comes from the battery (and it would charge), if the car is drawing more energy that the wall is providing, the deficit comes from the battery.

The situation where the battery is fully (or close to fully) charged, it's a little more nuanced. The on-board charger is still connected to the HV battery and the rest of the car, and the on-board charger tries to match the amount of power drawn from the wall to the amount that the car and the battery is consuming. The idea is to have the same result, use wall power to run the car unless there isn't enough. The reality is that this isn't a precise operation, and the car may either consume a little battery or the battery may charge a bit, even though it isn't supposed to.