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Warming the car and battery from shore power - 60a Wall Connector helpful

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So there is a lot of debate in the forums about how large a circuit to install for the UMC or whether to install a Wall Connector or not. Some folks advocate that not very much charging current is needed. Others lobby for as high power of charging options as possible.

As the weather has turned colder here in Portland Oregon (which still does not really get that cold) I have been warming my Model 3 LR RWD before I leave the house by using the Tesla app. I have then been using my Sense Energy Monitor to see how much power the car is drawing. (note that I have a Wall Connector on a 60a circuit so my car can charge at a full 48a)

Here is a graph of usage this evening as I fired up the heat to give a friend a test drive. The car had been cold soaked as it had not been driven in about 24 hours. I think the cabin reported 49 degrees Fahrenheit before starting HVAC. The car was charged to 80% the day before when I got home from work and had drifted down to 78% as it does most days overnight. The car did not attempt to charge the battery while it was heating. I did not give it a chance to warm up fully before we hopped in and went for a drive (regen was limited still and the cabin was not fully warm).

The key takeaway here: The car is able to make use of 10,500 watts of power just to heat the cabin (and maybe the battery?). That is about 44 amps of current at 240v!

So if you don't have that much shore power available, I am curious what the car does?

Does the cabin / battery warm up slower due to limited shore power?

Does it use battery power to heat up instead?

Regardless, I find this to be interesting data! I personally love having the ability to pre-warm the car and battery off shore power and I am happy with my Wall Connector install on a 60a circuit. ;-)
Screen Shot 2018-12-01 at 10.42.39 PM.png


This is the same graph, but with the cursor selecting the house baseline load before the Tesla started charging.
Screen Shot 2018-12-01 at 10.42.57 PM.png


Basically my callout is that just because you can fully charge your car for your milage needs overnight on some smaller circuit does not mean it is the optimal solution.

If the car does presumably use battery in order to bring the interior up to temp then you are putting more wear and tear on your battery (charge/discharge cycles) than is necessary.
 
The car is able to make use of 10,500 watts of power just to heat the cabin (and maybe the battery?). That is about 44 amps of current at 240v!
That strikes me as implausible: 10.5kW of shore power being used to heat the cabin when the interior temp is just 49F?

I do not know if at that moment any power was being used to warm the battery, but I doubt it; apparently your air temp was well above freezing.

When you got in the car and started driving, was the regen limited?
 
Doesn't the Model 3 use only the motor(s) to heat the battery (even when stationary), rather than having a separate heater? So the car can use a LOT of power while plugged in -- not limited to the size of the heater like in the X/S. I don't know how much power it actually uses, but the amount it COULD use is high.
 
Something doesn't seem quite right about your numbers. 44A @240 is more than your house ac probably uses.
I've got a feeling you may be off by a decimal point

House was drawing 471 watts before I turned on car heat. Then it peaked around 10,905 watts. So that is 10,434 watts into the car. 10434 / 240v = 43.475 amps.

Yes it is more than my AC uses by at least double. Though AC units are just moving heat from inside the house to outside the house. The car is using pure resistive heating to heat the inside of the car and maybe the battery too. If you have ever watched backup heat strips kick in on a household furnace, they draw an insane amount of power (say 25,000 watts at my friends cabin).

I am pretty positive my numbers are solid. That is why I created this thread since it seemed like a lot and I figured others would want to know!

That strikes me as implausible: 10.5kW of shore power being used to heat the cabin when the interior temp is just 49F?

I do not know if at that moment any power was being used to warm the battery, but I doubt it; apparently your air temp was well above freezing.

When you got in the car and started driving, was the regen limited?

So note that this current was not sustained for very long (maybe only a minute or two). Then it dropped down a bit. Since it was only 49F I am guessing that the heater would not have run for all that long at full bore (but still, even just bringing up the temp by a few degrees it will probably run at full power to start). I created a different thread just to post some of this raw data a couple weeks ago. There are a few more example graphs from different morning temperatures and letting it run different amounts of time over in this other thread:

Shore power usage during morning warmup

Regen was limited. I think had I let it pre-heat for much longer it would have warmed the battery (it seems anecdotally to me like it warms the battery even though we don't get an icon in the app indicating this).

My guess would be the car started charging as well as cabin heat.

I am pretty positive this is not the case. I charge to 80% every day when I get home (takes 45mins to an hour). The car then cools down overnight (parked outside) and in the AM I usually have 78% battery. If I pre-heat the car (even for over an hour) I go out there and the car has 78% battery still. So yeah, pretty sure it is not charging.

Also, on my Sense graphs charging is always a solid flat line (unless it is being charged to 100% and we are in the final 7% or so of the charge where it is tapering off). Here is an example of a (short) charging session: The car pulls a full 11.5kW to charge.

Screen Shot 2018-12-02 at 10.06.26 AM.png
 
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My experiment was using remote s and turning the climate control on and off as the charge was tapering. Temperature was moderate at 45. At 95 percent (I was headed for a long trip). At 240V, the car was drawing 24A without battery heat and 35A with. So that would be about 10A x 240 or 2.4KW.

Wasn’t clear from your post if you had set it to charge but I don’t see it drawing more.

The car was also not totally warmed and was regen limited even at the relatively warm temperature. It was cold soaked though. We only have a 50A circuit so main finding is to set it so the car charges to 100% as u leave. And then set climate on an hour ahead. It’s nearly perfect as the battery takers a lot at 95% the battery heating tapers up. This is on an M3
 
My experiment was using remote s and turning the climate control on and off as the charge was tapering. Temperature was moderate at 45. At 95 percent (I was headed for a long trip). At 240V, the car was drawing 24A without battery heat and 35A with. So that would be about 10A x 240 or 2.4KW.

Wasn’t clear from your post if you had set it to charge but I don’t see it drawing more.

The car was also not totally warmed and was regen limited even at the relatively warm temperature. It was cold soaked though. We only have a 50A circuit so main finding is to set it so the car charges to 100% as u leave. And then set climate on an hour ahead. It’s nearly perfect as the battery takers a lot at 95% the battery heating tapers up. This is on an M3

I would not expect battery heat to be necessary after a charging session (typically) since the charging would have been warming the battery?

I have my car set to charge to 80% all the time, but in this case, since it had charged the day before I do not believe it attempted to charge at all while warming the car up.

I think you are right in that if you want totally maximum available range, you want charging to finish just as you are getting in the car to leave and you want it fully warmed up (cabin and battery) from shore power. This will result in maximum range.
 
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Charging the battery afaik does not warm it. U need to turn on the climate control to get it to actually warm to operating temperature. I should have also mentioned the cabin temp was at 68 and set at 68 so there was basically no draw from the cabin.

I also FYI turn cabin up to 80 to see and the draw went up again by about 5A. So st least for my car at that temp. 10A for battery heat and 5A for cabin.

We normally set the car to start charging so it just reaches 100% about 30 minutes before we leave (a little buffer since that last 99-100 takes a long trickle). Then when we get up to shower and shave flip on the climate control. This worked fine on the MX. But on the M3 it seems to need more preheat so may use the scheduling feature of remote s or the new stats app to turn on climate control an hour ahead of time.

You have the full 48A available though so you may need less. We have 40A
 
It’s way less than your house heater uses though. 100,000 BTU = 29.3kW. Resistive heaters use way more power than AC.
I've got 2 HVAC zones and the AC compressors are on 40A and 30A breakers. It's a stupid big house (welcome to TX). :rolleyes: Theoretically they could draw up to about 55A but in use they don't use nearly that much. If they're both running they pull a little over 9kW (roughly 38A).
 
I've certainly seen a good 9A just running climate when I open the X's door without starting the car and still hooked to shore power. And that's probably cooling. The X/S heaters are supposedly around 6 kW. I wouldn't be surprised at 10 kW if the battery was being heated as well.
 
The Chevy Volt can show 5-6 kW draw when pre-conditioning the car. When on shore power, it draws more than the 3.6 kW on-board charger can provide - so draws a bit from the battery pack. So it wouldn't surprise me if the Model 3s heater could be just that much more powerful.
 
I am pretty positive this is not the case. I charge to 80% every day when I get home (takes 45mins to an hour). The car then cools down overnight (parked outside) and in the AM I usually have 78% battery. If I pre-heat the car (even for over an hour) I go out there and the car has 78% battery still. So yeah, pretty sure it is not charging.

Also, on my Sense graphs charging is always a solid flat line (unless it is being charged to 100% and we are in the final 7% or so of the charge where it is tapering off). Here is an example of a (short) charging session: The car pulls a full 11.5kW to charge.
Next time set your charge target level to below the current level, to be sure it is not charging. Then you can be more certain that it is just heating cabin and battery that is drawing the bulk of the power.
 
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Charging the battery afaik does not warm it. U need to turn on the climate control to get it to actually warm to operating temperature.

Hrm, I thought the whole point of the battery heater was to warm it for charging purposes. Also, charging should warm the battery just as a side effect of charging.

Next time set your charge target level to below the current level, to be sure it is not charging. Then you can be more certain that it is just heating cabin and battery that is drawing the bulk of the power.

I tried this today when I left for lunch after the car cold soaking overnight.

Here was the starting state of battery and temp:

3E6B09EE-F879-4546-BF36-E9407FD45D43.png


I set the charge limit lower:
A70FC6B3-37FE-40CD-985C-A36C31F5773F.png


I started heating the car:
01869187-ED36-411F-A898-8D68039C9325.png


Here is the peak consumption as it fired up:
EB6DADC3-1BCA-4F0E-A5CD-7C2BBBC9BBE6.png


Here is it oscillating (it always does this - seems like it is hunting for a temperature by keeps over correcting)
31411A18-F8C5-40D8-928B-842D1236D5C8.png


So yes, I am pretty positive that vehicle warm up (cabin plus maybe battery) can suck a *ton* of shore power.
 
Isn't that 3 kW vs. 11 kW you were getting before? Maybe I don't understand the graph.

Oh sorry, I did not explain. Ignore all those annotations along the line of the graph. That is the sense trying to tell you state changes and how many watts they are. It works fine for lighting loads and heating loads, but things that have VFD’s or are otherwise modulated via electronics it really does not work well for as they ramp up and down smoothly.

What you are seeing is that the sense thinks the last jump up on power ramp was 2843 watts. If you look at the first graph I posted I had the cursor selected on the peak and then it shows the bottom right value as 11,664 watts.
 
Oh sorry, I did not explain. Ignore all those annotations along the line of the graph. That is the sense trying to tell you state changes and how many watts they are. It works fine for lighting loads and heating loads, but things that have VFD’s or are otherwise modulated via electronics it really does not work well for as they ramp up and down smoothly.

What you are seeing is that the sense thinks the last jump up on power ramp was 2843 watts. If you look at the first graph I posted I had the cursor selected on the peak and then it shows the bottom right value as 11,664 watts.
I'm still not getting it. Your first graph shows what you were reporting as heating only, and it was at 11 kW, then you showed charging only, and it was 12 kW. Then you turned off charging by setting your charge level lower, and got 3 kW. That says to me that your first graph was not just heating, that the car was also charging, and that just heating is around 3 kW.

Not sure how you get anything different from your data.
 
I'm still not getting it. Your first graph shows what you were reporting as heating only, and it was at 11 kW, then you showed charging only, and it was 12 kW. Then you turned off charging by setting your charge level lower, and got 3 kW. That says to me that your first graph was not just heating, that the car was also charging, and that just heating is around 3 kW.

Not sure how you get anything different from your data.

Sorry, this is confusing I think for folks that don't have a Sense unit and know what the different numbers mean. It also does not help that I switched from the web client app to the phone app and the two display data differently.

Now that I am back at my laptop, here is a graph (from the web interface) of the entire warming cycle from me going to lunch today. Looks like I gave it fifteen minutes of warmup time before unplugging it to leave.

The house was drawing about 1000 watts before I fired up the car heat (that is the red line at the far left of the graph). The overlaid graph of orange is solar generation - that can be entirely ignored in this conversation.

Then I have my cursor over the highest peak point which is 11664w at 11:57am. That is when I fired up the car heat. So I read that as about 10.5kW of energy being consumed by the car while the car was NOT charging (just warming). Even after the initial spikes moderate, it is still drawing 6kW or more of power.

Screen Shot 2018-12-02 at 8.20.11 PM.png