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

[North75]

So does anyone know of any way to determine whether any of that is battery heating via the drive unit?
Can the cabin heater draw that much power when it first turns on? Will the cabin heater draw high current until the heating element gets hot?

 

[lolder]

There is no dedicated battery heater in the M3. Ingineerix examination of engineering screens indicate that the battery may not be heated or cooled between -7.5º C. and 48º C ( 20 to 118 º F. ). It is doubtful that preheating the cabin has a direct effect on battery temperature.
I have seen 7+ kw drawn by the resistive cabin heater. That's very powerful when you consider it only takes about 17 kw to go 70 mph

 

[BerTX]

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.

Ok, so we agree that your first graph shows about 11 kW. What does the last graph show, when you had the heat on but forced charging to be off?

 

[Richt]

Super interesting. Pretty consistent with what I saw. I didn’t look at the initial burst but the longer term draw which looks like 3kW or about 10A. Sounds like it spikes to 30A then drops. Good work!

 

[eprosenx]

Ok, so we agree that your first graph shows about 11 kW. What does the last graph show, when you had the heat on but forced charging to be off?

When I said "first graph" I meant the first one in this post:
Warming the car and battery from shore power - 60a Wall Connector helpful

Not the first one at the top of the thread.

That last graph I posted here was the test where I set charging down low so there was no way it would kick in: Warming the car and battery from shore power - 60a Wall Connector helpful

I am pretty confident all this power draw is not going to battery charging.

None of these graphs show just 3kw of increase. They show much more than that. Look at the scale on the left.

 

[Richt]

There is no dedicated battery heater in the M3. Ingineerix examination of engineering screens indicate that the battery may not be heated or cooled between -7.5º C. and 48º C ( 20 to 118 º F. ). It is doubtful that preheating the cabin has a direct effect on battery temperature.
I have seen 7+ kw drawn by the resistive cabin heater. That's very powerful when you consider it only takes about 17 kw to go 70 mph

They use the motor to heat the battery. The climate control is lashed to the interior climate control. It has nothing to do with it but appears to be the only way to the battery heating on (assuming u do not have range mode on)

 

[BerTX]

When I said "first graph" I meant the first one in this post:
Warming the car and battery from shore power - 60a Wall Connector helpful

Not the first one at the top of the thread.

That last graph I posted here was the test where I set charging down low so there was no way it would kick in: Warming the car and battery from shore power - 60a Wall Connector helpful

I am pretty confident all this power draw is not going to battery charging.

None of these graphs show just 3kw of increase. They show much more than that. Look at the scale on the left.

Thanks, I see it now. Sorry about not understanding.

 

[rdlink]

My main question (unrelated to heating) is why Sense can't identify the HPWC. I mean, come on. My charger kicks in at 3:00 AM every morning, and the draw jumps almost immediately from ~550W to ~12,000W. And when charging is done it almost instantaneously drops back. I've never charged past about 82%, so there is no tapering.

 

[lolder]

My main question (unrelated to heating) is why Sense can't identify the HPWC. I mean, come on. My charger kicks in at 3:00 AM every morning, and the draw jumps almost immediately from ~550W to ~12,000W. And when charging is done it almost instantaneously drops back. I've never charged past about 82%, so there is no tapering.

The car doesn't need to taper the charge from it's onboard AC to DC charger until it is close to 100%. The charge taper is at superchargers.

 

[ecarfan]

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.

thanks for the explanation. Good to know!

 

[eprosenx]

My main question (unrelated to heating) is why Sense can't identify the HPWC. I mean, come on. My charger kicks in at 3:00 AM every morning, and the draw jumps almost immediately from ~550W to ~12,000W. And when charging is done it almost instantaneously drops back. I've never charged past about 82%, so there is no tapering.

Yeah, you would think the Sense could identify that easily (since any human can easily see what is going on).

The issue though as it has been described to me is that there is not really any easily identifiable spike or surge when the car starts charging that the Sense can easily key off of. Most of the devices Sense can easily identify have large inrush currents (like a motor or a solenoid). Or a ballast firing up...

The Tesla's have been built intentionally to soft start. They slowly ramp up their charge rather than engaging all at once. This is easier on the electrical system and the Tesla components. It is hard for the Sense to look for signatures over such a long time period of ramp up I suspect.

The car doesn't need to taper the charge from it's onboard AC to DC charger until it is close to 100%. The charge taper is at superchargers.

So I accidentally charged my car to 90% after messing around with the charge settings in this thread (I meant to set it back up to 80%). I noticed during that charging session that the charge tapered at the end. I thought that was interesting as I thought taper did not start till after 90%. (my Wall Connector is on a 60a circuit so it can supply a full 48a to the car) I wonder if this taper started earlier due to the battery not being warm enough?

 

[SageBrush]

The oscillations of the power draw are I suspect not from the heating components so we may just be looking at a battery replenishment cycle. If so, then a lower rated EVSE would just have a different cycle.

 

[ℬête Noire]

Yeah, you would think the Sense could identify that easily (since any human can easily see what is going on).

The issue though as it has been described to me is that there is not really any easily identifiable spike or surge when the car starts charging that the Sense can easily key off of. Most of the devices Sense can easily identify have large inrush currents (like a motor or a solenoid). Or a ballast firing up...

The Tesla's have been built intentionally to soft start. They slowly ramp up their charge rather than engaging all at once. This is easier on the electrical system and the Tesla components. It is hard for the Sense to look for signatures over such a long time period of ramp up I suspect.



So I accidentally charged my car to 90% after messing around with the charge settings in this thread (I meant to set it back up to 80%). I noticed during that charging session that the charge tapered at the end. I thought that was interesting as I thought taper did not start till after 90%. (my Wall Connector is on a 60a circuit so it can supply a full 48a to the car) I wonder if this taper started earlier due to the battery not being warm enough?

View attachment 357713

Interesting. That's only a roughly 20% drop-off, so on a circuit limited to 32A it shouldn't start tapering yet (48A * .8 = 38.4A), and probably wouldn't until sometime into the 90's. Was the starting SOC around 72-75%? Eyeballing it (without opening the jpg in PaintX to count pixels) I'd estimate the tapering starter around 87% SOC, so maybe 92% or so is where a 32A (40A breaker) circuit would start tapering, assuming that taper remained that linear (probably a safe assumption here).

I run my how charger at 28A**. I've never checked the taper but that means it should start tapering at around 93%. I'll try check that the next time I'm prepping for a trip.

** I turned down the charge at home to 28A because I cooked my 32A J1772 charging station, replacing it on warranty. When I say "cooked" I mean it got hot enough that it melted a hole in the back and left a black scorch spot on the drywall behind. I'm guessing it was borderline on going to flames, but was oxygen starved enough that it just sooted the interior before the breaker threw. I'd used the charger daily for several with the Bolt, it seems that the Model 3 LR will pull more than the Bolt even though the Bolt will nominally take the full 32A as well?

 

[eprosenx]

The oscillations of the power draw are I suspect not from the heating components so we may just be looking at a battery replenishment cycle. If so, then a lower rated EVSE would just have a different cycle.

I am really positive that this is not showing any kind of battery charging.

Also, I have never seen a Tesla charge a battery with anything other than a flat line of constant current (except when the battery is almost full and then it tapers off as a flat line).

 

[lolder]

Yeah, you would think the Sense could identify that easily (since any human can easily see what is going on).

The issue though as it has been described to me is that there is not really any easily identifiable spike or surge when the car starts charging that the Sense can easily key off of. Most of the devices Sense can easily identify have large inrush currents (like a motor or a solenoid). Or a ballast firing up...

The Tesla's have been built intentionally to soft start. They slowly ramp up their charge rather than engaging all at once. This is easier on the electrical system and the Tesla components. It is hard for the Sense to look for signatures over such a long time period of ramp up I suspect.



So I accidentally charged my car to 90% after messing around with the charge settings in this thread (I meant to set it back up to 80%). I noticed during that charging session that the charge tapered at the end. I thought that was interesting as I thought taper did not start till after 90%. (my Wall Connector is on a 60a circuit so it can supply a full 48a to the car) I wonder if this taper started earlier due to the battery not being warm enough?

View attachment 357713

That's not much of a taper and would be none on a 14-50 outlet UMC 32 amp charger. 48 amp/240 is 11.5 kw which looks like where your chart is most of the time. The real tapering is from 120 kw superchargers after 50-60 % charge.

 

[AlanSubie4Life]

I posted this somewhere else, but you can see the heater usage directly on the car, you don't have to have any Sense unit (as long as you don't mind hanging around and observing - the plots are nice, though!).

HVAC (Heater) Really Does Use a Lot of Energy

Plug in, set charge threshold below the current state of charge, crack driver's door to make the screen stay on, and you can play around with the heat settings on the app, and see how much you're drawing. It just shows up on the screen. There's a static 2A in my car, with the heat off, so you can subtract that. I was able to get up to about 6kW or so, and it was 68 degrees in the car and I was heating to 72 or so. It tapers off pretty quick of course for these small differentials.

Of course, battery heating is probably a factor here too (it wouldn't have been in my case). It would be interesting to do the same sort of experiment at a cold temperature - I think once the cabin comes to temperature you could see the battery warming contribution (the displayed amps minus 2 amps standby current) - though probably there is some static load from the resistive heater too - but it's going to be a lot less than the peak resistive heat, when you first turn on the heater. There may be a way to see that by turning down the set point - but not sure whether the battery will immediately stop warming once the cabin setpoint is below the cabin temperature (I have no way to experiment with this since it's not really cold). Seems like it might be sufficient for the climate control to simply be "on" in the app even if it's not actively heating. I haven't played around with it.

Anyway, you'd want the wall connector so you have the 48A available, to see whether you can max the draw from that, but I was just using a UMC. I didn't max it out for my scenario since it wasn't remotely cold (maybe 65 in the garage), but seems like it wouldn't be difficult as 11kW isn't really all that much power.

Overall, not surprising at all. Chevy Spark EV shows the power draw directly, and you can get it up to 8kW for a while, if the car is at 50 degrees and you turn the heat to "MAX". Then it tapers to 2-3 kW. Not surprised at all to see the Model 3 resistive heat will exceed 10kW! I would hope so; you want the car to be nice and toasty! Otherwise everyone would be complaining.

It would be nice to see a direct display of kW draw from the battery at all times (like the Spark)...would eliminate confusion and help people with their optimization, possibly.

A heat pump would be great for California, though!