Understanding the battery heater

[AWDtsla]

apparent degradation if you change to 90% (maximum daily) rather than 80%.

Apparent is the key word. You can only get the BMS more or less badly calibrated. I'm quite sure now that it hides most degradation anyway. You will only find out how much degradation you have when you try and get close to 0 miles.

Every Li-ion study in existence says higher SoC is worse for degradation. Nothing special about the Panasonic cells in your Tesla.

 

[Lanber]

My 2 cents with 4 years and 160.000km is the BMS now has more conservative limits on powerlevels when battery is cold / semi cold than in previous software versions.

 

[Terry S]

The current cold weather initiated battery heating is useless,they need to allow us to turn it on with the app and set the temp.
I can hardly use regeneration during the winter and it doesn’t get that cold in Vancouver. Not to mention the range drops dramatically.
I use my ludicrous batt heater mode to heat my batt in morning, but I have to go down to the car to do it at least half hour before I leave. The fart app may be funny for men and some decerning women, but a battery preheat on demand option on the Tesla app, should take precedence to a fart app, though Whimsy is important.

 

[AWDtsla]

The current cold weather initiated battery heating is useless,they need to allow us to turn it on with the app and set the temp.
I can hardly use regeneration during the winter and it doesn’t get that cold in Vancouver. Not to mention the range drops dramatically.
I use my ludicrous batt heater mode to heat my batt in morning, but I have to go down to the car to do it at least half hour before I leave. The fart app may be funny for men and some decerning women, but a battery preheat on demand option on the Tesla app, should take precedence to a fart app, though Whimsy is important.

Tweet Elon and hope he notices. Never noticed mine.

Model S has been out for nearly 7 years now. There are some things Tesla just doesn't understand, and maybe never will.

 

[David99]

The current cold weather initiated battery heating is useless,they need to allow us to turn it on with the app and set the temp.
I can hardly use regeneration during the winter and it doesn’t get that cold in Vancouver. Not to mention the range drops dramatically.
I use my ludicrous batt heater mode to heat my batt in morning, but I have to go down to the car to do it at least half hour before I leave. The fart app may be funny for men and some decerning women, but a battery preheat on demand option on the Tesla app, should take precedence to a fart app, though Whimsy is important.

Heating up a battery takes a lot of energy. The colder it is the more it takes (obviously). 4-6 kWh easily from a very cold night parked outside. The most you can get back from regen on a 25 mile drive is 1.6 kWh. You are spending more energy overall.

When you use the app to preheat the cabin, the battery heater will turn on as well and heat up the battery to a reasonable temperature. It will stop once the battery is aprox at 8-10 C / 46-50 F. That gives the car plenty of power and a good amount of regen. Heating it more is wasting more and more energy for little to no benefit.

The best way to have your battery warm in the morning and using as little energy as possible, is to start the charging process at night at the right time so it finishes just before you are about to leave. Charging the battery will warm it up using the heat losses in the chargers and battery itself. There are apps that automate this process. Tesla should implement this into the car. Let the owner set a departure time and the car will start charging automatically at the right time.

 

[AWDtsla]

The most you can get back from regen on a 25 mile drive is 1.6 kWh. You are spending more energy overall.

What an incredibly generic statement. Imagine your drive starts out as a 1500 ft decent. This is not hard to do. Pretty much did that a couple days ago.

When you use the app to preheat the cabin, the battery heater will turn on as well and heat up the battery to a reasonable temperature. It will stop once the battery is aprox at 8-10 C / 46-50 F. That gives the car plenty of power and a good amount of regen. Heating it more is wasting more and more energy for little to no benefit.

No, not even close enough for reasonable supercharging. Not only are you holding yourself up, but you're holding up the all the other Tesla's trying to use the supercharger. I don't find anything reasonable about that temperature.

The best way to have your battery warm in the morning and using as little energy as possible, is to start the charging process at night at the right time so it finishes just before you are about to leave. Charging the battery will warm it up using the heat losses in the chargers and battery itself. There are apps that automate this process. Tesla should implement this into the car. Let the owner set a departure time and the car will start charging automatically at the right time.

Just. Give. Me. Control. Of. The. Heater.

 

[David29]

....
When you use the app to preheat the cabin, the battery heater will turn on as well and heat up the battery to a reasonable temperature. It will stop once the battery is aprox at 8-10 C / 46-50 F. That gives the car plenty of power and a good amount of regen. Heating it more is wasting more and more energy for little to no benefit.
...

This is what I have always understood as well. But lately I am less certain about this. I have noticed that the red asterisk, the indicator of battery being heated, stays on only briefly when I preheat the car lately. And also, to my surprise, i have seen that red asterisk on the phone screen in the past few days, when the car was not plugged in to shore power. I had always understood the battery heater works only if the car has a 240V source.
I spent a few minutes searching the latest owner's manual, and i find no description of when the battery heater operates.

 

[BrokerDon]

The best way to have your battery warm in the morning and using as little energy as possible, is to start the charging process at night at the right time so it finishes just before you are about to leave. Charging the battery will warm it up using the heat losses in the chargers and battery itself. There are apps that automate this process. Tesla should implement this into the car. Let the owner set a departure time and the car will start charging automatically at the right time.

100% agreed. We should be able to set the charging COMPLETION time so the battery and interior are both optimized for departure. Completely doable in software although calculating the charging time will be tricky the colder the ambient temperature is.

 

[AWDtsla]

This is what I have always understood as well. But lately I am less certain about this. I have noticed that the red asterisk, the indicator of battery being heated, stays on only briefly when I preheat the car lately. And also, to my surprise, i have seen that red asterisk on the phone screen in the past few days, when the car was not plugged in to shore power. I had always understood the battery heater works only if the car has a 240V source.
I spent a few minutes searching the latest owner's manual, and i find no description of when the battery heater operates.

I've noticed from logs that it at least toggles the battery heater flag at various times, when it shouldn't even be on. Noticed this while supercharging with a hot battery last weekend. Flag was on for the first 2 minutes, with no apparent purpose.

 

[David99]

I've noticed from logs that it at least toggles the battery heater flag at various times, when it shouldn't even be on. Noticed this while supercharging with a hot battery last weekend. Flag was on for the first 2 minutes, with no apparent purpose.

Yes I think Tesla has been adjusting the BMS recently (or maybe a few months ago). I see a different behavior on my car in terms of battery temp management. One thing I recently found it (not sure that was always the case), when charging at a Supercharger, the BMS will turn on the battery heater when the battery is below aprox 25 C / 77 F. That is significantly warmer than the normal cut off temp for the battery heater (around 8-10 C). It seems when it comes to fast charging, Tesla wants the battery warm. Although what you described sounds more like a bug. I have also recently notice when I stop after driving for a while, the fans go full blast even though I can see on the CAN bus the battery is not hot at all and I have been driving normal so nothing could have gotten hot. Seems rather random.

 

[David99]

100% agreed. We should be able to set the charging COMPLETION time so the battery and interior are both optimized for departure. Completely doable in software although calculating the charging time will be tricky the colder the ambient temperature is.

This feature could start charging an hour or two before it needs to and to see what the actual charge rate is. Once it has a reading, it can make a pretty accurate estimate and set the start point. If you also select preconditioning, it would automatically 15 min to the time.

The app I'm using to do this right now is kind of doing it that way. It starts by calculating the start time based on SoC and desired level. An hour before it's supposed to start, it usually does a test charge, then adjusts the start point and sometimes it interrupts the charging process if it turns out it would finish too early. It actually always re-checks the conditions and adjusts on the fly. It also accounts for preconditioning.

 

[David99]

I had always understood the battery heater works only if the car has a 240V source.
I spent a few minutes searching the latest owner's manual, and i find no description of when the battery heater operates.

The battery heater will come on when the battery is cold and you turn on the car or use the app to preheat it. It doesn't have to be plugged in. This winter I was paying more attention to when the heater comes on (looking at the CAN bus message) and it definitely does come on a lot. You can turn it off by switching Range Mode on. I believe Tesla doesn't want to bother the owners with battery temperature so it's mostly hidden and no manual access. I think it's a good decision. Personally I would love to have access to every detail of the car of course

 

[AWDtsla]

The battery heater will come on when the battery is cold and you turn on the car or use the app to preheat it. It doesn't have to be plugged in. This winter I was paying more attention to when the heater comes on (looking at the CAN bus message) and it definitely does come on a lot. You can turn it off by switching Range Mode on. I believe Tesla doesn't want to bother the owners with battery temperature so it's mostly hidden and no manual access. I think it's a good decision. Personally I would love to have access to every detail of the car of course

It actually does the OPPOSITE of what you'd want. If you're plugged into a charger, it will run the pack heater less than if it isn't. So - burn a bunch of juice when you just want to warm the cabin, and don't use shore to heat the pack when available. Perfect.

 

[Benjanos]

This is an interesting thread to learn how/when this heater is functioning. Thanks.

BTW, the BMW i3 I had worked somewhat as people here are requesting, here is my recollection of how BMW did it.....
1) To make all of this work, there was a departure time setting in the SW. Not ideal if you are not exactly sure when you will be leaving for each trip and not ideal if you forget to change the last departure time to your next departure time (if they are different)
2) The departure time setting also interacted with the 'off peak' charging setting which could be confusing. I.e. the car would override the 'off-peak' time slot if it thought it could not charge in time for your next departure (fair enough)
3) You could program the car to preheat the battery. It took 3 hours or something so the preheating of the battery was linked to the departure time. There was no 'preheat battery now' button. It also warned you this was not efficient and only for a max range scenarios. Also it would only preheat the battery if connected to shore power, but see next point
4) Because the charge cable supplied with the car was not able to provide enough power to run the heaters, you would anyway leave with less than 100% charge. I guess to make the whole thing work properly I would have needed a beefier supply to the car at the time
5) The charging of the car was also linked to the departure time (unless you told it to charge immediately) so the battery was warm from charging when you departed, but this would then collide with the battery heater, so again if you didn't have a enough AC supply to the car, guess what happened...

So there you go folks, that's how BMW did it, probably a little too confusing for Grandma to master.

Right or wrong, Tesla probably took a look at the i3 approach and said "hmmm... lets keep it simple, our battery is 4 time bigger anyway"

 

[Terry S]

Heating up a battery takes a lot of energy. The colder it is the more it takes (obviously). 4-6 kWh easily from a very cold night parked outside. The most you can get back from regen on a 25 mile drive is 1.6 kWh. You are spending more energy overall.

When you use the app to preheat the cabin, the battery heater will turn on as well and heat up the battery to a reasonable temperature. It will stop once the battery is aprox at 8-10 C / 46-50 F. That gives the car plenty of power and a good amount of regen. Heating it is wasting more and more energy for little to no benefit.

The best way to have your battery warm in the morning and using as little energy as possible, is to start the charging process at night at the right time so it finishes just before you are about to leave. Charging the battery will warm it up using the heat losses in the chargers and battery itself. There are apps that automate this process. Tesla should implement this into the car. Let the owner set a departure time and the car will start charging automatically at the right time.

My drive consists of a lot of downhill initally and I have use my brakes a lot , as long as I am plugged in at home I don't mind using the extra energy to bring the temp to 15 or 20 deg. C. My range is also much better at those temp's. If I don't heat it regeneration doesn't work to level I like all day.
So what if it cost's me 30cent, it's 10 times cheaper than my truck. I want the option to heat the batt especially when I have my 300+km drive 1 or twice a week

Heating up a battery takes a lot of energy. The colder it is the more it takes (obviously). 4-6 kWh easily from a very cold night parked outside. The most you can get back from regen on a 25 mile drive is 1.6 kWh. You are spending more energy overall.

When you use the app to preheat the cabin, the battery heater will turn on as well and heat up the battery to a reasonable temperature. It will stop once the battery is aprox at 8-10 C / 46-50 F. That gives the car plenty of power and a good amount of regen. Heating it more is wasting more and more energy for little to no benefit.

The best way to have your battery warm in the morning and using as little energy as possible, is to start the charging process at night at the right time so it finishes just before you are about to leave. Charging the battery will warm it up using the heat losses in the chargers and battery itself. There are apps that automate this process. Tesla should implement this into the car. Let the owner set a departure time and the car will start charging automatically at the right time.

I have only had the batt heat icon go on by itself once or twice, if I heat the cabin It doesn't heat the battery utilizing the batt heater, it adds a little heat the electric heat draw, but that only is on for 5 min to get the cabin warm,so I have almost zero regeneration in the morning unless I manually put on the ludicrous batt heater.
I do not have a pridictable schedule usually so I cannot risk delayed charging.

 

[Terry S]

What an incredibly generic statement. Imagine your drive starts out as a 1500 ft decent. This is not hard to do. Pretty much did that a couple days ago.

No, not even close enough for reasonable supercharging. Not only are you holding yourself up, but you're holding up the all the other Tesla's trying to use the supercharger. I don't find anything reasonable about that temperature.



Just. Give. Me. Control. Of. The. Heater.

Yes give me control!!!

 

[hybridbear]

The app I'm using to do this right now is kind of doing it that way. It starts by calculating the start time based on SoC and desired level. An hour before it's supposed to start, it usually does a test charge, then adjusts the start point and sometimes it interrupts the charging process if it turns out it would finish too early. It actually always re-checks the conditions and adjusts on the fly. It also accounts for preconditioning.

What app is this? What does it cost?

 

[David99]

What app is this? What does it cost?

Android app called 'Dashboard for Tesla'. If you don't have an Android phone, get an Amazon Fire tablet for $49. Does the trick and doubles as a nice tablet for lots of other things. You just need to have a constant internet connection because that's how the app communicates with the car.

 

[David99]

I do not have a pridictable schedule usually so I cannot risk delayed charging.

Then use worst case scenario and set it to finish at the earliest you might leave in the morning. That's still better than starting to charge at 6 pm when you come home, be done charging at 10 pm and have the battery get cold for the next 10 hours.

I'm also not understanding the obssesion with regen. Why does it matter that you have limited regen? The brakes work just fine. You know that heating up the battery to the point where you have full regen would waste much more energy than you can recover compared to having limited regen. There is nothing to gain. That's exactly why Tesla set the BMS to do it that way.

BTW, the state of charge also affects regen. Based on my measurements, the SoC needs to be below 85% to get full regen. Anything above reduces regen.

 

[hybridbear]

Android app called 'Dashboard for Tesla'. If you don't have an Android phone, get an Amazon Fire tablet for $49. Does the trick and doubles as a nice tablet for lots of other things. You just need to have a constant internet connection because that's how the app communicates with the car.

I'm going to check it out. I have an old Nexus 7 tablet that I used with my Ford EVs for years. Hopefully it will be able to install the Dashboard for Tesla app.

Then use worst case scenario and set it to finish at the earliest you might leave in the morning. That's still better than starting to charge at 6 pm when you come home, be done charging at 10 pm and have the battery get cold for the next 10 hours.

I'm also not understanding the obssesion with regen. Why does it matter that you have limited regen? The brakes work just fine. You know that heating up the battery to the point where you have full regen would waste much more energy than you can recover compared to having limited regen. There is nothing to gain. That's exactly why Tesla set the BMS to do it that way.

BTW, the state of charge also affects regen. Based on my measurements, the SoC needs to be below 85% to get full regen. Anything above reduces regen.

You're exactly right from a physics perspective. It doesn't make sense to spend a lot of energy heating the battery just to have regen from a total energy consumption expense. But humans are creatures of habit & many people are resistant to change. That's essentially what's happening here. People don't like the inconsistent driving experience of varying amounts of regen. Other EVs don't limit regen when it's cold so their driving experience is consistent.

I have always done the delayed charging like you propose. My previous EVs were usually set to begin charging at 3:00 am. This is near the minimum daily demand for the electric grid so it's the best time for the grid. It's also the best time for having the warmest battery temp when departing in the morning. For my smaller battery EVs (Fusion Energi & Focus Electric) that I had years ago they would charge in 2-3 hours. The Tesla often wouldn't need much more than that for charging, and often less. The only time I would have to adjust this is when there would be an unusual situation of arriving home with a low SOC followed by an early morning departure with the need for a high SOC. Otherwise I was always able to start charging late & thus have more regen. But that is too much thinking for a lot of people.