This is my recommended method, as I hate to waste energy, wear/tear, etc... doing "nothing". I use TeslaTasks to schedule a charge, which I'll need to do anyway, before I leave.
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MY Battery Barely Warming Up
- Thread starter Stach
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This is my recommended method, as I hate to waste energy, wear/tear, etc... doing "nothing". I use TeslaTasks to schedule a charge, which I'll need to do anyway, before I leave.
Rshephorse
Member
Rshephorse
Member
My only question is that it is better to drain the battery when it is cold than it is to [super] charge the battery when it is cold. Charging a cold batter apparently leads to more imbalance and battery degradation? and I'm not sure if that's really only true for DC Super charging and not for home AC charging....
I was thinking that I would charge when I got back home, when the battery was warm from driving- and run climate in the am while it's still plugged in, that way I'd get the battery and windows/charge port/locks all defrosted...
I have an OBD2 reader installed, so I'm interested in how fast charging vs climate vs just driving warms a battery that is down around freezing or lower...
Rshephorse, your concerns are interesting but the BMS takes care of all that for you. If the battery's too cold, it will charge more slowly and some power will be used to heat it up until it can accept more charge. It's more a matter of convenience: if the battery's already warm, it will charnge faster. In a supercharger session that's a major difference in time lost waiting for the charge on a trip. At home? Not so much of a difference. You can them wait and charge at night so it ends when you'Re about to leave. That way you use the charge as a way to keep the battery warm for when you need to drive.
Draining the battery when it is cold does not harm the battery. The colder the temperature the less efficiently the battery both charges and discharges. The lithium-ion battery is a chemical battery, all chemical reactions have an optimum temperature for the reaction. Much below that temperature or too much above the optimum temperature and the reaction slows. For a lithium-ion battery the optimum temperature for operation is ~80F +/- perhaps 5 or 10 degrees. Charging a lithium-ion battery requires monitoring the temperature of the battery; the lithium-ion battery will be irreparably damaged if it is charged when the temperature is below 32F. When the temperature is below 32F, if a lithium-ion battery is charged dendrites (elongated crystals) will form within the cell that will result in a loss of capacity. Of greater concern is that eventually if a dendrite grows large enough it will cause a short circuit within the battery cell that will cause the battery overheat, could result in a battery fire. Discharging a cold lithium-ion battery does not risk forming dendrites, the downside of colder battery temperatures just means that the battery can deliver less power. At extreme cold temperatures, i.e. below about -24F the battery will not be capable of providing enough power to drive the vehicle until the battery pack has been warmed
You are correct that if you charge your vehicle as soon as you arrive back home the battery will already be warm and charging will be somewhat more efficient than if you wait until the battery has cooled down to start charging. The battery is a very large mass and it takes many hours for a warm battery pack to fully cool down to the point that would impact charging. If the battery pack gets too cold, the battery management system will first warm the battery pack before initiating a charging cycle. Warming the battery will use some energy and slightly extend completion of the charging cycle; this is unavoidable as the battery must be warm enough to avoid being damaged before charging.
For Supercharging the goal is to charge as quickly as possible, usually this involves charging the battery to no more than 70% or 80%, as can be done safely given the charging limits of the battery. This requires careful management of the charging voltage and current while Supercharging along with monitoring the temperature of the battery pack, charging cable and charging connector. The reason that Tesla warms the battery if you set your destination to include a stop at a Supercharger is so the battery pack is at the optimal temperature for charging. It will not harm the battery pack if it is temporarily allowed to be warm, the battery management system will cool down the battery pack once charging has been completed.
In warm weather it won't matter if you charge as soon as you arrive home or set delayed charging. In cold weather it is better to use delayed charging, to complete charging as late as possible. In my experience the Tesla delayed charging algorithm will start charging at the beginning of the delayed charging time you set, i.e. 11PM or 12AM or 1AM, else if you set delayed charging to start as late as possible then charging will always be completed by 0600AM, probably by ~0550AM. The delayed charging algorithm appears to take into account that across multiple parts of the national electric energy grid peak energy usage starts at 0600 AM so delayed charging will always complete charging before this time. If, after delayed charging has just completed, you start driving at 0600AM the battery will be warm and you won't see a blue snow flake next to the battery charge indicator, may not see any "......." indicating that regenerative braking is limited. If you don't start driving until 3 hours later the battery will have cooled slightly but not enough that you would see the blue snowflake although you might experience a reduction in regenerative braking. Tesla appears to limit regenerative braking when the temperature of the battery pack is below 40F. (Regenerative braking is a form of charging and cannot be performed if the battery pack is too cold, else the same issue exists of forming dendrites that will damage the battery cells.)
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