They used that as an example, and I am not sure why you are focused on "its not necessary to plug the car in" when its also true that its "not necessary to NOT plug the car in". Both statements are true, so I am not sure what your focus on that part of this is. Plugging the car in or not is not going to have anything to do with the thread question, which is heat in the garage.
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Is the car keeping my garage warm?
- Thread starter Vinnigan
- Start date
They used that as an example, and I am not sure why you are focused on "its not necessary to plug the car in" when its also true that its "not necessary to NOT plug the car in". Both statements are true, so I am not sure what your focus on that part of this is. Plugging the car in or not is not going to have anything to do with the thread question, which is heat in the garage.
A couple of points about the Tesla using AC power for preconditioning the battery and/or cabin.
That would only be true if AC charging was always at a level that would satisfy the power demands of the HVAC compressor. AC charging can be performed at power levels that vary from ~1kW up to 11.5kW, yet the Tesla Model Y will precondition the passenger cabin and battery as required regardless of the AC power being provided. The compressor (high voltage) can draw up to ~7 kW. Battery warming is performed by stator warming draw 3.5kW per drive unit, total of ~7kW. Combined, the HVAC compressor and the stators can draw ~15kW. That is well in excess of the 11.5kW charging rate when charging at 240V and 48 amps. The only available source for that much power is the high voltage battery.
Also, there is no redundant wiring, i.e. the AC wiring only connects to the PCS. The PCS steps up the voltage and only sends power to the battery via high voltage wiring harness. The battery sends high voltage to the components that require high voltage DC through high voltage wiring harnesses.
So you're saying... there's no such thing as AC power being used for anything other than charging the battery?
That is my conclusion. Even the low voltage system in the Tesla Model Y can draw close to 2kW (This would be in excess of the power available from a 120V/15 amp circuit, maximum power of this circuit is 1.44kW.) Everything is logical if the high voltage power provides all power when the Tesla Model Y is in Standby mode, being driven, etc.
When the Tesla Model Y is in Sleep mode when only a few low voltage systems require power, i.e. the door locks, vehicle alarm sensors (does not include the cameras and Sentry mode), BT modem, LTE modem the low voltage lithium battery module provides the needed power. The high voltage battery will charge the low voltage battery via the DC-to-DC converter circuitry in the PCS as required.
The older design that used a 12V lead-acid battery could go ~24 hours before needing to be charged from the high voltage battery. The new low voltage lithium battery module has much less capacity than the lead-acid 12V so unless Tesla reduced the power usage in Sleep mode the low voltage lithium battery module would require charging multiple times over 24 hours. This could account for some of the increased power usage Tesla Model Y owners are observing while their Tesla vehicle is parked. The Tesla Model Y (other models too) must wake up from sleep mode, enter Standby mode so that the DC-to-DC converter can charge the low voltage lithium battery module, for perhaps 1 hour, multiple times per day. If the low voltage battery requires charging from the high voltage battery/DC-to-DC converter 4 times over 24 hours, each charging session lasting 1 hour, the estimated consumption would be ~1kWh every 24 hours just to top up the low voltage lithium battery. (All numbers are estimates.)
supergeek
Member
This is mostly true, but to understand how the AC system lets the car run purely off of the AC inverter you need to understand a bit about how batteries charge.
In order to charge or discharge a battery, you need to change the voltage of the system. You can draw a huge amount of current/amps through the circuit, but as long as the onboard inverter is able to keep the voltage stable the batteries won’t be charging or discharging.
As far as I’m aware, the batteries, charger/inverter, and all the HV loads are just wired up in parallel like the circuits of your house. Power doesn’t have to go “through” components but it can go “past” them.
There is no fixed, guaranteed level of AC mains power so that the Tesla Model Y can always assume there is sufficient power to run the HVAC compressor, perform stator warming and run the low voltage systems.
Perhaps if there was a schematic. I can picture wiring in series, not in parallel. I don't believe Tesla would use two separate high voltage wiring harnesses for the AC compressor (one from the battery and the other from the PCS).
My understanding of how the Tesla Model Y is powered, charged (AC charging):
Mains Power (AC) => PCS (steps up voltage from 120V/240V to 400V, rectifies power to DC) => High Voltage Battery.
Mains Power (AC) => PCS => DC-to-DC Converter (This would enable powering some of the low voltage system, charging the low voltage battery directly from the Mains (my conjecture.) Note that this would not be applicable when Supercharging as there is no AC mains source.
High Voltage Battery => DC-to-DC Converter => Low Voltage system (powers low voltage systems and charges the low voltage battery as required.)
High Voltage Battery sends 360V+ DC power => HVAC Compressor
High Voltage Battery sends 360V+ DC power => Drive unit power control units (converts DC back to AC) => Front and rear drive units' motors for driving and power wave for stator warming.)
Silicon Desert
Well-Known Member
Not to dispute your quote, I'll say people just do what works for them and their driving habits. For me, I don't plug it in daily anymore since I wore out the connector on my 2017 MX from plugging in daily for years and had to have it replaced. Now I can use the excuse that I am just too lazy to do that every day.
House AC -> Charger (PCS) -> HV DC
HV DC <-> Pack (<- if loads exceed house power)
HV DC -> LV DC (PCS) (16V or so)
HV DC -> Compressor
HV DC -> Drive Units (<- during regen)
If, for instance, a car is preconditioning off of a 12A 120V connection, it will draw from both house AC and pack DC seamlessly.
What about during a Supercharger (SC) charging session? Does it matter that the SC DC voltage is higher than 400V (i.e. higher than the high voltage battery voltage)?
I was at the supercharger this week and I noticed a lot of steam coming from my car. I looked over and the car across from me was also steaming. This leads me to believe that the charging process gives off a lot of heat.
What I’d like to know is if I set my M3 to charge to 80% overnight and then the car sits for a couple of days, would the car automatically charge back up to 80%?
Or do I have to tell the car to charge back to 80%?
Mariano
It will charge back up after it loses about 3-4%, automatically. Whether thats a few hours or a few days (or longer) depends on how much the car is using while sitting there (is it sleep? Cabin overheat protection on? Sentry mode on? Checking car a lot in the app? etc).
SC HV DC -> HV DC
The Supercharger voltage is whatever is takes to achieve the vehicle’s requested charge current, but never more than the pack maximum voltage at the car. There is voltage drop from cabinet to pedestal and pedestal to car.
Well if you've got an ice vehicle parked in there with your Tesla, then your question is kinda moot - because we all know ice gets super hot and will hold temps for a long long time in a garage. Park the ICE outside all evening & overnight, then check the temp after only having the Tesla in the garage.
Here is how to check your Tesla's battery temp, if interested. How to see a Tesla's battery temperature - EVchargerReviews.net
Ahh, sorry that’s a misunderstanding. The ICE car doesn’t get driven much so when I made the initial observations the ICE car had been parked for /days/ at that point.
This was just a quip about how I later /also/ noticed that the ICE car puts out a lot of heat after being driven.
electricar
Member
When it’s 110F outside our garage is a lot cooler when we both get home and park our 2 Teslas than with our previous dino burners. The heat in the garage was so brutal with the ICE cars for hours until they cooled down that the rooms adjacent to the garage got hotter.
i do the same...i only charge once it's in the 20s or 30% range.
charge it up to 90% and i drive maybe 2-3 days a week.
set it to charge during off peak hours and have car conditioned to be ready by the time i leave for work.
i do notice that the garage temps are a lot higher then but other than that, i don't ever notice.
25-30 degrees of "heat" sounds quite odd, even if the car is plugged in on the time. I definitely haven't noticed anything. But then again, I have a 2 car tandem garage that has 700sqft of floor space and 13foot high ceilings. Is your garage a single car, smaller garage?
I don't know for sure what the operating range is of a Tesla battery is - I've read somewhere in the 75 degrees F range, but not really sure.... But a cast iron (or aluminum) lump of metal in an ICE vehicle certainly is hotter than that, and once the car is shut off, I imagine it maintains that heat for quite a while. So I think it's safe to say that an ICE vehicle pulled into a garage is going to heat it up more than your Tesla.
supergeek
Member
When your Tesla is charging it tries to keep the battery at 80f for minimal wear. It's less about the thermal mass, but the fact that it's keeping the battery warm for many hours while it's charging. In the winter we'll notice our garage will be a little warm in the morning even though the car finished charging 3 or 4 hours ago. I've often turned the car on to pre-condition in the morning and it's already 78 in the cabin sitting in the garage 
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