Can Wall connector bypass car for heating battery directly?

[zivac87]

How does heating battery during winter time works when wall connector is plugged in?
Does it bypass charging and starts heating battery directly from wall, or does it need to fill up a battery and use that energy to heat it?
I want to put least amount of strain on it and I hate to top it off by a tiny bit multiple times daily

 

[vanwho]

If the car is plugged in but not charging, as far as I can tell, it uses the energy directly from the charger to run the heater/pumps, etc., and does not charge and pull from the battery, unless the plug doesn't give enough electricity.

 

[zivac87]

Great! Thanks for clarification!

 

[davewill]

"Bypassing" the battery isn't really a thing. These is only one High Voltage bus. When heating the battery, the power comes from that bus. If you're plugged in, but not needing to charge, the on-board charger will try to bring in enough wall power to offset whatever is being used to heat the battery,. If there isn't enough coming in, then the extra will have to come from the battery.

 

[zivac87]

"Bypassing" the battery isn't really a thing. These is only one High Voltage bus. When heating the battery, the power comes from that bus. If you're plugged in, but not needing to charge, the on-board charger will try to bring in enough wall power to offset whatever is being used to heat the battery,. If there isn't enough coming in, then the extra will have to come from the battery.

Thanks, it make sense, but to clarify; When I turn on defrosting to heat battery and car, if it needs no more then what wall connector can provide it doesent impact battery cycles at all?

If it needs 14 kW and charger provides 11 kW it impacts battery cycle for this tiny 3 kW extra that system needs from battery while heating?

I know we shouldn't stress over such things but over years which i plan to keep my car it could affect my battery.

 

[beatle]

Thanks, it make sense, but to clarify; When I turn on defrosting to heat battery and car, if it needs no more then what wall connector can provide it doesent impact battery cycles at all?

If it needs 14 kW and charger provides 11 kW it impacts battery cycle for this tiny 3 kW extra that system needs from battery while heating?

I know we shouldn't stress over such things but over years which i plan to keep my car it could affect my battery.

Yes, that's right.

Are you trying to decide if you should leave your car plugged in and topped off vs. going out into the cold to plug it in at the right time to charge it back up before you leave? If so, I guess it's your car and your butt going out into the cold, but you're missing one of the key features of an EV, which is to be able to leave with a full battery and a warm cabin every day with zero input from you. To think the topping off might impact your battery's life is like not listening to the radio because it increases energy consumption by 100 watts. Your battery is far, far more likely to suffer a random failure than it is to have a shortened life by 0.001 extra battery cycles over the life of the car.

 

[zivac87]

Yes, that's right.

Are you trying to decide if you should leave your car plugged in and topped off vs. going out into the cold to plug it in at the right time to charge it back up before you leave? If so, I guess it's your car and your butt going out into the cold, but you're missing one of the key features of an EV, which is to be able to leave with a full battery and a warm cabin every day with zero input from you. To think the topping off might impact your battery's life is like not listening to the radio because it increases energy consumption by 100 watts. Your battery is far, far more likely to suffer a random failure than it is to have a shortened life by 0.001 extra battery cycles over the life of the car.

I keep my car plugged but i lower my charge 5-10% under current level so it doesent trigger when i know i dont need it for more than few kilometers. When its cold it uses significant power to warm everything when unplugged, around 1-2%, which i dont mind, but doing it 10 times during the day actually uses more power then my short few km trips. If it affects cycles for only that small amount when powered by 11 kW connector i dont care and ill use it constantly to keep my ass warm, but if i waste 10-20% of my battery cycle daily (for 10 trips) it is simply not worth it for me and ill rather drive while being cold.

 

[appleguru]

For teslas, a plugged in car is a happy car.

To answer your question, it depends a little bit on the specific model you have and its BMS firmware, but in general, there are 3 different charging states the car can be in:

1) “voltage mode”: In this mode, the car’s onboard AC -> DC charger is enabled and is providing power to the vehicle (eg to heat the battery), but the actual contactors to the HV battery itself are open/not connected. In this mode, the battery does not charge.
2) “power mode”: This is the normal AC charging mode. In this mode, the HV battery is being charged by the car’s inverter/charger at a specified voltage and current.
3) “DC fast charge mode”: in this mode, the onboard charger and is bypassed, and the chargeport is directly connected to the HV battery. The external charger manages the DC voltage and current going to the battery.

When it’s cold out and you leave your car plugged in to AC power, its BMS will switch between the first two modes automatically. If, for example, your battery is charged to your set level and you enable the car’s HVAC, it will use “shore power” (via “voltage mode”) to run the HVAC and will not need to draw from the battery.

 

[zivac87]

For teslas, a plugged in car is a happy car.

To answer your question, it depends a little bit on the specific model you have and its BMS firmware, but in general, there are 3 different charging states the car can be in:

1) “voltage mode”: In this mode, the car’s onboard AC -> DC charger is enabled and is providing power to the vehicle (eg to heat the battery), but the actual contactors to the HV battery itself are open/not connected. In this mode, the battery does not charge.
2) “power mode”: This is the normal AC charging mode. In this mode, the HV battery is being charged by the car’s inverter/charger at a specified voltage and current.
3) “DC fast charge mode”: in this mode, the onboard charger and is bypassed, and the chargeport is directly connected to the HV battery. The external charger manages the DC voltage and current going to the battery.

When it’s cold out and you leave your car plugged in to AC power, its BMS will switch between the first two modes automatically. If, for example, your battery is charged to your set level and you enable the car’s HVAC, it will use “shore power” (via “voltage mode”) to run the HVAC and will not need to draw from the battery.

Its '23 MS Plaid, and thank you guys for answers it was really helpful. It makes me use my app and heating when car is plugged without worrying.

 

[davewill]

Thanks, it make sense, but to clarify; When I turn on defrosting to heat battery and car, if it needs no more then what wall connector can provide it doesent impact battery cycles at all?

If it needs 14 kW and charger provides 11 kW it impacts battery cycle for this tiny 3 kW extra that system needs from battery while heating?

I know we shouldn't stress over such things but over years which i plan to keep my car it could affect my battery.

Yes, of course it does, but it should not be a significant amount...besides your only alternative would be to get into a cold car, which I'm sure you would then proceed to heat while you're driving in which case ALL of the heating power will be coming from the battery.

 

[airborne spoon]

Thanks, it make sense, but to clarify; When I turn on defrosting to heat battery and car, if it needs no more then what wall connector can provide it doesent impact battery cycles at all?

If it needs 14 kW and charger provides 11 kW it impacts battery cycle for this tiny 3 kW extra that system needs from battery while heating?

I know we shouldn't stress over such things but over years which i plan to keep my car it could affect my battery.

It depends on the charger you're plugged into if I'm at home and using the tesla HPWC it charges up to 19kW and the heater doesn't ever seem to draw that much. if the battery is full it'll just draw power from the wall not the battery, if you are using a lower powered connector to the wall then it'll draw as much as it can from the wall and take the rest from the battery. Once the battery is warmed up and it turns off if the battery has dropped below the threshold for turning the charger back on then it will otherwise it'll just stop drawing power and hang out like normal.

 

[zivac87]

It depends on the charger you're plugged into if I'm at home and using the tesla HPWC it charges up to 19kW and the heater doesn't ever seem to draw that much. if the battery is full it'll just draw power from the wall not the battery, if you are using a lower powered connector to the wall then it'll draw as much as it can from the wall and take the rest from the battery. Once the battery is warmed up and it turns off if the battery has dropped below the threshold for turning the charger back on then it will otherwise it'll just stop drawing power and hang out like normal.

Unfortunately new cars are limited with 11 kW onboard chargers, but I noticed even when its really cold, it only uses 1-3 km of range from battery when connected to HPWC, which should have negligible impact on HV battery over its life.

 

[ucmndd]

1) “voltage mode”: In this mode, the car’s onboard AC -> DC charger is enabled and is providing power to the vehicle (eg to heat the battery), but the actual contactors to the HV battery itself are open/not connected. In this mode, the battery does not charge.

Do you have any sort of documentation about this “mode”? In 6 years, 160,000 miles, and countless preconditioning events I can’t recall a single instance where the car was awake and drawing power from the wall without the HV contactors closed.

 

[appleguru]

Do you have any sort of documentation about this “mode”? In 6 years, 160,000 miles, and countless preconditioning events I can’t recall a single instance where the car was awake and drawing power from the wall without the HV contactors closed.

It’s in the model S charging section in the “theory of operation” docs on tesla’s service site.

 

[davewill]

1) “voltage mode”: In this mode, the car’s onboard AC -> DC charger is enabled and is providing power to the vehicle (eg to heat the battery), but the actual contactors to the HV battery itself are open/not connected. In this mode, the battery does not charge.
2) “power mode”: This is the normal AC charging mode. In this mode, the HV battery is being charged by the car’s inverter/charger at a specified voltage and current.
3) “DC fast charge mode”: in this mode, the onboard charger and is bypassed, and the chargeport is directly connected to the HV battery. The external charger manages the DC voltage and current going to the battery.

When it’s cold out and you leave your car plugged in to AC power, its BMS will switch between the first two modes automatically. If, for example, your battery is charged to your set level and you enable the car’s HVAC, it will use “shore power” (via “voltage mode”) to run the HVAC and will not need to draw from the battery.

Do you have any sort of documentation about this “mode”? In 6 years, 160,000 miles, and countless preconditioning events I can’t recall a single instance where the car was awake and drawing power from the wall without the HV contactors closed.

I have to say I'm confused, too. Isn't the BMS inside the battery pack on the battery side of the contactors? How could it open and close them? In fact with the contactors open, does the car know anything about the battery state? It would make more sense that the BMS simply told the on-board charger whether it wanted enough power to charge the battery or not, but left the contactors closed.

 

[beatle]

It’s in the model S charging section in the “theory of operation” docs on tesla’s service site.

I don't think HV should be flowing through the system without the contactors being closed. Disconnecting the safety loop will sever the 12v line that allows the contactors to close so that work can be performed on the HV system. If you could energize the HV bus without the contactors being closed, you'd have a pretty dangerous system, and that would mean disconnecting the safety loop wouldn't really mean much. It's also why a dead 12v battery will brick the car.

I have to say I'm confused, too. Isn't the BMS inside the battery pack on the battery side of the contactors? How could it open and close them? In fact with the contactors open, does the car know anything about the battery state? It would make more sense that the BMS simply told the on-board charger whether it wanted enough power to charge the battery or not, but left the contactors closed.

The car can still read info on the battery without the contactors being closed. Though the BMS is located inside the battery (on top, actually), It can report out to the CAN bus via low voltage signals. It has its own DC/DC converter to run off the battery directly.

This doc has some good info on the HV system:

https://static.nhtsa.gov/odi/tsbs/2013/SB-10052460-6095.pdf

The BMS takes this measurement inside the battery contactors, which is why the values observed on the TDS will be different depending on the contactor state.​

​

This is a good video of the BMS: