Charge pre-heating

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m3_4_wifey

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#1
With a new software update coming that includes the car pre-heating the battery before it gets to a Supercharger, I'm curious how long the Model 3 needs to pre-heat the battery from say an outside temperature of 20F. Also, can we get that function for just pre-heating the battery before I leave my garage if I tell my car the destination is a Supercharger 15 miles away?

Here in Vermont, we usually charge the car in the morning to help the battery heat up a bit and then turn on the climate a little early, which takes no time to heat up the car, but still takes time to heat up the battery. I feel like there is still a lackofcontrol on pre-heating the battery for a long trip when you want to optimize the range in cold climates.
 

GDN

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#2
This brings up an interesting point if I can tag on to your questions. It's been the belief that the car used the excess heat from the motor to heat the battery already. We also know that in extreme conditions it can do this without the motor turning. If this is really true, and if the battery is more efficient when it is warmed up, why wouldn't they already be doing all they can to heat the battery (or cool if necessary in the summer) without knowing you are headed to a SC.

I know that v3 is going to introduce charging rates we've never seen before, so maybe they are just having to up the game a bit, but I would have thought they were already heating or cooling as necessary to keep the battery optimum.
 

m3_4_wifey

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#3
This brings up an interesting point if I can tag on to your questions. It's been the belief that the car used the excess heat from the motor to heat the battery already. We also know that in extreme conditions it can do this without the motor turning. If this is really true, and if the battery is more efficient when it is warmed up, why wouldn't they already be doing all they can to heat the battery (or cool if necessary in the summer) without knowing you are headed to a SC.

I know that v3 is going to introduce charging rates we've never seen before, so maybe they are just having to up the game a bit, but I would have thought they were already heating or cooling as necessary to keep the battery optimum.
Yeah, I question how efficient the waste heat mode is to heat the battery when the car is not moving. Tesla did some sthing to simplify the car, but the waste heat mode may not be strong enough to fully pre-condition a cold battery and a stationary car. When the car is moving, you have waste heat from the motor and the battery itself that you can steal from.

I'm holding onto the hope that before next winter the Tesla app. will have the option to condition the battery, condition the climate, or both.
 

m3_4_wifey

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#5
What gives you the impression the battery has a variable efficiency?
1552438854849-png.23187


However the main effect on a long trip is that your battery is not spending time heating up the giant brick under your feet. If your battery brick is already warm you probably don't need to use as much heat on the cabin extending your range. I realize that this probably is not worth it for short trips, but every bit helps on the long ones.
 

iChris93

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#6
View attachment 23187

However the main effect on a long trip is that your battery is not spending time heating up the giant brick under your feet. If your battery brick is already warm you probably don't need to use as much heat on the cabin extending your range. I realize that this probably is not worth it for short trips, but every bit helps on the long ones.
Yes, of course resistance decreases with increased temperature. But is it significant?
 

iChris93

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#8
Do you have anything to add other than another question?
Sorry, I’m just trying to understand. I don’t think looking at a decrease in resistance is enough to say the effeiciency of the battery changes in one direction or the other.
 
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garsh

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#9
...if the battery is more efficient when it is warmed up, why wouldn't they already be doing all they can to heat the battery (or cool if necessary in the summer) without knowing you are headed to a SC.
Yes, of course resistance decreases with increased temperature. But is it significant?
It's not as significant as the amount of energy needed to warm it up. That's why Tesla doesn't heat it with any more than normal waste heat under normal circumstances.

Also, can we get that function for just pre-heating the battery before I leave my garage if I tell my car the destination is a Supercharger 15 miles away?
I love this idea. I'd gladly waste a little energy to have full regen available on cold days.
 

JasonF

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#10
How "waste heat" from the AC motor can heat the battery when the car isn't moving:

If you've ever seen a "locked rotor" AC motor with power applied, it gets really, really hot very quickly. A variable-frequency drive (like the one that moves the Model 3 motor) can simulate that by setting the frequency at a rate that doesn't actually rotate the motor. Then the heat can simply be carried away by the coolant and sent to the battery.

The advantage is that would use about a tenth of the wattage that a resistive heater would use. Disadvantage is it's slightly slower, because the heat source isn't in the battery.
 

JWardell

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#11
As you know, you can already pre-heat your battery while triggering charging a few hours before you leave.

As this passes current through a stationary motor to create heat, the question is how they will achieve the new pre-supercharge feature while the model 3 is moving.
Maybe they will just try to add heat whenever the car is stopped at a traffic light etc? But I don't think that is significant enough at the current 5kW rate.

Maybe they can run the phases slightly out of sync or some other bad method when driving to reduce efficiency and create heat, but I think the driver would be able to feel something not right.

If we can't figure it out I will try to trigger it some day and log data to see what is different.
 

JasonF

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#13
Only an advantage if efficiency of conversion to heat is the same.
I can't do math, so I don't know the efficiency numbers.

But what's more obvious is less parts, less weight, less complexity, and no chance of both a heater and motor drawing power at the same time. In which case it might not be "best" for battery warming, but it's the "best" solution overall.
 

m3_4_wifey

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#14
Maybe they can run the phases slightly out of sync or some other bad method when driving to reduce efficiency and create heat, but I think the driver would be able to feel something not right.

If we can't figure it out I will try to trigger it some day and log data to see what is different.
I agree with running the signals to the stators in an inefficient manner to generate heat while the car is moving at any speed, and then scrounge the waste heat to the battery. I guess if the battery is cold and you drive steady for a couple miles, and then tell the computer to navigate to a supercharger, you could watch to see how much the energy usage steps up. Go for it if you have another way to capture the data.

Tesla needs to give options on pre-conditioning the battery. I only care about this for a long trip, or when I want full regen/performance, but 30 minutes before I leave my garage, I'm going to tell it to navigate to the nearest Supercharger and see if all the dashes go away faster than if I just let it charge like normal in the morning and partially heat up. We'll see if this hack works once the update gets rolled out.
 

m3_4_wifey

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#15
Sorry, I’m just trying to understand. I don’t think looking at a decrease in resistance is enough to say the effeiciency of the battery changes in one direction or the other.
Temperatures in the 20-30C range mostly allows for better current flow out of the battery. Batteries at low temps probably still deliver near the same amount of total kwh that a warm battery does (battery resistance effect is probably small). However, as someone living in cold Michigan, you should want to maximize the storage of both thermal and electric energy when you're taking that long trip to grandma's.
 

JWardell

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#16
I forgot one more way to generate heat while moving: brakes.
The car could automatically apply the brakes lightly while compensating with the motor. If done right it would drive normally, but require a lore more power to drive, generating a bit more heat. However most of the energy would be brake heat wasted to the air, so not a very efficient solution.
 

PNWmisty

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#17
Maybe they can run the phases slightly out of sync or some other bad method when driving to reduce efficiency and create heat, but I think the driver would be able to feel something not right.

If we can't figure it out I will try to trigger it some day and log data to see what is different.
It's always interesting to look at data logs and learn more about all the complex programming that went into the car. So thank you for your work there.

I think it's pretty obvious your idea of running the motor purposefully inefficiently is the ONLY way to do it. They will map new torque curves for the inefficient "battery heating mode" so the driver won't feel a thing, it will respond just as if the mode were not engaged (the SOC will just drop faster). If they get a little fancy, they will even phase out the inefficient motor programming at higher output levels (like if you're driving 120 mph on the Autobahn, or passing a car). At high output levels the motor should be producing around 15% of consumption as heat anyway. Maybe someone really tuned into how their motors sound could notice a slight difference in tone between the normal mode and battery heating mode but I think it'll be pretty invisible to the driver. Basically, more current will be going through the windings for the same amount of motive force.

There are a lot of ways to waste electricity to save a few precious minutes and apparently, that is what consumers think they want. Another way to achieve the same thing (consume more electricity/save precious minutes) is to drive at 95 mph 30 minutes prior to arriving at the SC. This could save even more time because the wasted electricity is mostly spent getting you there even sooner (assuming it's not so cold that this doesn't warm the battery sufficiently). The upside is you don't even need battery heating mode to use this technique, the downside is you need either diplomatic immunity against traffic tickets and/or a radar detector and some risk tolerance.;)
 
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JoeP

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#18
he upside is you don't even need battery heating mode to use this technique, the downside is you need either diplomatic immunity against traffic tickets and/or a radar detector and some risk tolerance.
Perhaps Tesla's should just have an RFID sender that broadcasts to local law enforcement that they're on the way to a supercharger and shouldn't be ticketed since they're saving the planet by increasing efficiency?
 

m3_4_wifey

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#19
I forgot one more way to generate heat while moving: brakes.
The car could automatically apply the brakes lightly while compensating with the motor. If done right it would drive normally, but require a lore more power to drive, generating a bit more heat. However most of the energy would be brake heat wasted to the air, so not a very efficient solution.
I was thinking about something similar in the case of a dual motor car. You could have the front motor pulling the car foward and the rear motor doing regenerative breaking. This would cause more current going in and out of the battery and create more waste heat without wearing out the break pads. However, I think the Tesla engineers are smarter than this and can just create heat running one motor more inefficiently so it works for both the rear motor and dual motor vehicles.
 

PNWmisty

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#20
I was thinking about something similar in the case of a dual motor car. You could have the front motor pulling the car foward and the rear motor doing regenerative breaking. This would cause more current going in and out of the battery and create more waste heat without wearing out the break pads.
That would save the brake pads but it would be hell on the tread life!