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Optimal Battery Temperature

Discussion in 'Battery Discussion' started by doubeld, Aug 17, 2015.

  1. doubeld

    doubeld Member

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    I am not currently a BEV owner, so I'm just trying to get a handle on how the cold will affect BEV uptake for myself, and any other people in my region (Calgary, AB) that I happen to have this conversation with. For starters, I'm a winter person. I love snowboarding - backcountry, as well as on the resorts - so I park the car for hours/days at a time outdoors in less than optimal temperatures. I do lots of road trips in the winter and most of my driving overall. Fortunately I have a garage so a BEV would be warm most of the time.

    I know that cold temperature affects a battery's usable capacity. I also know that using a battery causes it to heat up.

    Where is the happy medium? What temperature would it have to be outside for the battery to not have to engage heating or cooling elements? Say at 100km/h. What about when parked?

    Is there an easy answer to all this? Sorry if this has been answered already, couldn't find exactly what I was looking for.
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    1. Don't leave it outside in -32 C or colder weather for 24 hours or more (this is in the manual).

    2. The battery is liquid cooled/heated, so to a point, ambient temperature isn't really an issue as the car tries to maintain the correct temperature. Keep it plugged in whenever possible (even plugged into 110V is better than nothing).

    3. Preheating and setting the charge start time so that it finishes about the time you start driving lets you start out with a warm battery.

    4. Not doing #3 reduces range (sometimes dramatically) because the heating elements have to use up range to get to the correct temperature. Range mode can mitigate this to some extent, but not in very cold weather.

    5. Hot weather is much less of an issue.
     
  3. David99

    David99 Active Member

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    Temperature is a two sides thing with Lithium batteries. Higher temperatures are good for performance and power. You can charge and discharge them faster when they are warm. The chemical reactions just work better. The downside is also the bad chemical reactions, the ones that cause the battery to degrade over time, are accelerated. So while a warm battery is good for using the car, lower temperatures are better for long term battery life.

    This is where the large Tesla battery has a great advantage, even when it's cold the reduced performance and capacity is plenty to drive the car.

    There is nothing we can about the weather. If you live in hot climates like Arizona, there is little you can do to keep the battery cooler than the ambient temperature. Same with cold climates.

    Tesla will heat or cool the battery when it reaches certain low or high levels. It's especially noticeable when you charge at a Supercharger which heats up the battery. Or when the car was parked outside in a very cold environment. But once the temperature is within the normal range it doesn't seem to actively cool or heat it. It would be a waste of energy for very little to no effect. Even when temperatures are normal the car will circulate the coolant here and there even when the car is just parked. It makes sure all cells are always kept at the same temperature. Same when driving. Even when the battery temperature is normal, the coolant pump keeps running to even out temperature all the time. Different cell temperature would lead to uneven charge and discharge and put the battery out of balance.

    In cold weather, it is a good idea to time the charging in a way that in finishes in the morning, just before you want to leave. That way the charging will warm up the battery. The car will also turn on the battery heater if it gets really cold and it's best to get that power from the grid when charging. Otherwise the car will uses it's battery to heat itself which costs a lot of range.
     
  4. DMC-Orangeville

    DMC-Orangeville 85D and John Deere 5100E

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  5. Lloyd

    Lloyd Active Member

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    This is why Tesla needs to enable a 'Finish charge by XXXX time' is important!
     
  6. David99

    David99 Active Member

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    Absolutely. It would make a lot of sense for many reasons. It would keep battery degradation lower, it would perfectly preheat the battery, it would take the guesswork out of the owner's head. I'm surprised it's not a feature yet.
     
  7. doubeld

    doubeld Member

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    Thanks for the blog link - haven't seen this section yet! Great info there. Tesla, and all the other BEV manufacturers seem to all have lots to learn about winter driving issues, many which Tesla seems to have addressed. No doubt this will get polished in future upgrades/models.

    If anything, I've learned that I would spare no expense to get the highest kWh rating car available :)

    As mentioned in Doug's blog, it would be nice to see battery and motor temperature readings. Again, something that is available and may hopefully make it into a 'diagnostic info' screen at a later date. Information is king.
     
  8. David99

    David99 Active Member

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    I'm pretty sure Tesla is hiding it on purpose and it makes sense. The battery management keeps the battery healthy and within good temperatures. Tesla has a feature that will automatically pre heat your car based on your daily routine.

    The problem with giving the driver information about something they have no control over is just a cause of worry. I remember my old VW Golf. The coolant temperature gauge showed the temperature go up when you started it in the morning and then it stayed at the same level all the time. I was happy thinking, wow great motor management. Later I installed a device that shows motor data. I saw the temperature go up and down as I drove but the car's temp gauge stayed the same. And then I realized that's exactly what the average driver wants. They want to look at the temperature and see it's OK. The fluctuation I saw actually happening are perfectly fine and there is no need to worry and adjust driving styles or anything.
    I think that's Tesla's concept as well. There is very little data or info. There is a warning message popping up when something is getting out of normal range, but other than that, the driver is not bothered with monitoring all kinds of data that would just make him or her feel they have to constantly keep an eye on it. I know the techies (like us) love to have all kinds of real time data, but it's just a cause of subtle worry for the normal driver.
     

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