SOC Setting?

[beeeerock]

I think most of us agree that there's a sweet spot in any battery somewhere between >20% and < 100%. But the other interesting point this guy made was to store your battery at a lower voltage. If you aren't jumping in the car immediately, don't juice it to 100% (or maybe even 90%).

Which then begs the question... what is the sweet spot? 70%? 80%? It would be nice if Tesla made that advice public, because 90% of my days can be easily managed with a shallow cycle centered on whatever % makes sense. And if I do need to top up for a trip, I can do that at home or at the local Supercharger (if short notice) without too much inconvenience. Just because the warranty is 8 years and unlimited km's doesn't mean I want to abuse my battery pack.

 

[mknox]

Which then begs the question... what is the sweet spot? 70%? 80%? It would be nice if Tesla made that advice public, because 90% of my days can be easily managed with a shallow cycle centered on whatever % makes sense.

I don't think Tesla's said (officially) and I don't think they will. They want people to just use the car and not worry about these kinds of things, and let their battery management software take care of things. Having said that, I've always heard that lithium batteries like it best in the middle of their operating range. I use about 30% of my battery's capacity on my daily commute and that's why last summer I charged to 70% and ended my day around 40%. Gave me a bit of buffer in case I had some evening errands to run.

 

[jbcarioca]

That's not correct as i understand it. two 50% charges are less than one 100% full cycle. Two 25% charges are less than a 50% cycle. So if a battery has a 1000 100% cycles (just a number for ease of calculation), it could have 2500 50% cycles, and 7000 25% cycles. This has been posted with some real numbers someplace, but the idea is that shallow charges will extend the life of the battery. Of course, there's deterioration just based on the number of months, but that's separate from the effect of cycles.

From all that I have read that is true. Most public data treats li-ion behavior in generalisations. Specific chemistry, construction techniques, cell quality control battery load management and battery thermal management all alter durability and cycle wear tolerance. Thus, all the information we are exchanging is at best theoretical because Tesla and Panasonic do not completely disclose the proprietary technologies and techniques they use. I recall a handful of statements from tesla testimony before the NTSB. Those all stated that the Tesla approach reduced cell and battery sensitivity to ambient temperature and high charging​ loads. That last I bolded because Superchargers place enormous thermal loads on cells that Tesla has managed so well that they say Supercharging has no negative effect on the batteries. AmpedRealtor in post 38 quoted the really important part, that we should keep our Tesla's plugged in so the battery management system can manage thermal optimization. It follows that the specific resting charge level is probably well placed within generally accepted li-ion resting charge levels, i.e. ~30-80%. Full charge does present thermal questions, so should not be the resting state. Much below 30% and the margin for load reserve becomes too low. Between those broad limits it seems to me we are reflecting our own operational choices, while doing no harm.

If there are among us engineers who actually know the specifics for the Tesla specific chemistries and management technologies I, for one, would love to know more details.

 

[mknox]

AmpedRealtor in post 38 quoted the really important part, that we should keep our Tesla's plugged in so the battery management system can manage thermal optimization.

I'm not saying I disagree, and Tesla sure does emphasize the point. But I have no empirical evidence that having my car plugged in is doing anything other than when the car is actually charging or running the HVAC system. For example, if I plug my car in at 80% SOC with my slider set at 60%, I record absolutely no power draw on the logger I have on my outlet until many days later when the vampire drain causes the car to drop below 60% at which point a top up cycle will start. My car is in an unheated garage where temps can get into the high 90's in summer and well below freezing in winter and I've seen none of this "thermal management" outside of when the car is actually charging. So I question the value of plugging in when I do not need a charge. Am I missing something? Are others seeing something different?

 

[Cyclone]

My car is in an unheated garage where temps can get into the high 90's in summer and well below freezing in winter and I've seen none of this "thermal management" outside of when the car is actually charging. So I question the value of plugging in when I do not need a charge. Am I missing something? Are others seeing something different?

Is Range Mode on or off on your vehicle? I know that makes a difference when you turn on climate control while plugged in. I guess it would also matter what firmware you are on as posts have mentioned that changing or asking for it to change.

 

[mknox]

Is Range Mode on or off on your vehicle? I know that makes a difference when you turn on climate control while plugged in. I guess it would also matter what firmware you are on as posts have mentioned that changing or asking for it to change.

Although it may seem backwards, I typically use Range Mode in the summer, but not the winter. I find it has minimal effect in the winter with heat anyway, and use it in the summer mainly to keep the a/c compressor noise down to a dull roar. Often I don't leave the a/c on at all. I will over-ride a/c to OFF and Recirculate to Outside Air but leave Mode and Fan Speed on Auto.

As far as firmware, I've had the car over 2 years and so have had many, many flavors.

I've been thinking about this and have a theory: I think the car just does it's thing using the battery and not shore power when plugged in. When the SOC drops to a bit below the preset limit, the charger kicks in and simply tops it up again. Tesla probably wants the car plugged in so it doesn't trickle itself to zero without being able to top itself up periodically. When I'm on vacation for a week or more, I will leave my car plugged in with the slider at 60%. Typically, I will see 2.5 kWh of consumption on my energy meter every other day. The power is exactly consistent with the charging limit I've set in the car so it is clearly just doing top-ups.

 

[Cyclone]

I've been thinking about this and have a theory: I think the car just does it's thing using the battery and not shore power when plugged in. When the SOC drops to a bit below the preset limit, the charger kicks in and simply tops it up again. Tesla probably wants the car plugged in so it doesn't trickle itself to zero without being able to top itself up periodically. When I'm on vacation for a week or more, I will leave my car plugged in with the slider at 60%. Typically, I will see 2.5 kWh of consumption on my energy meter every other day. The power is exactly consistent with the charging limit I've set in the car so it is clearly just doing top-ups.

This would make sense and is the simplest explanation.

 

[Larry Chanin]

My take home: Top off as frequently as you can, but keep your voltage down unless you plan to drive immediately.

Yes, but don't keep your battery at too low a state of charge either.

The following reference speaks to the point that Jerry made in posting #36.

Advice Please: Charge Every Night or Not, posting #20


Theoretically if you don't plan to drive daily it's best to "store" the car at about 50% SoC preferably in a cool environment. However, most of us bought the car to drive it. :wink:

So if it's your practice to keep it at 50% SoC overnight then in terms of preserving the life of the battery it would be a good idea not to drive it very much during the day because to do so would yield a low SoC. Then a nightly charge to 50% would be an unnecessarily "deep" charge. In accordance with the reference linked above, deep charges take life off of the battery. So if a person drives a moderate amount during the day it would be unwise, and probably inconvenient as well, to charge to 50%.

Larry

 

[chriSharek]

From all that I have read that is true. Most public data treats li-ion behavior in generalisations. Specific chemistry, construction techniques, cell quality control battery load management and battery thermal management all alter durability and cycle wear tolerance. Thus, all the information we are exchanging is at best theoretical because Tesla and Panasonic do not completely disclose the proprietary technologies and techniques they use. . . . . . If there are among us engineers who actually know the specifics for the Tesla specific chemistries and management technologies I, for one, would love to know more details.

jbcarioca, if you are truly interested in the different chemistries employed by different companies, I strongly suggest you watch this presentation. It explains the additives to the Lithium ion solution and how these additives affect the battery life in different ways and how temperature has such a huge affect on things as well. He went so far to show some differences between Tesla, Nissan (I love the way he pronounces this) and the Volt.

- - - Updated - - -

Yes, but don't keep your battery at too low a state of charge either.

The following reference speaks to the point that Jerry made in posting #36.

Advice Please: Charge Every Night or Not, posting #20


Theoretically if you don't plan to drive daily it's best to "store" the car at about 50% SoC preferably in a cool environment. However, most of us bought the car to drive it. :wink:

So if it's your practice to keep it at 50% SoC overnight then in terms of preserving the life of the battery it would be a good idea not to drive it very much during the day because to do so would yield a low SoC. Then a nightly charge to 50% would be an unnecessarily "deep" charge. In accordance with the reference linked above, deep charges take life off of the battery. So if a person drives a moderate amount during the day it would be unwise, and probably inconvenient as well, to charge to 50%.

Larry

Thanks Larry. The way the car is set up to be charged by a specific departure time would also make sense to store it at lower SOCs and charge it JUST BEFORE heading out the door (depleting the charge) and thus minimizing the time the battery was at a high SOC.

 

[Panu]

Then a nightly charge to 50% would be an unnecessarily "deep" charge.

I didn't understand this. In my understanding DoD means how many % of battery capacity were used. But what is this "deep" charge?

If the recommendation is to keep SoC between 20% and 90% most of the time then it makes sense to me to let it sit at 50% when not driven as long as driving will not usually take it below 20%. Isn't that much better for the battery than letting it sit at 90% and drive it to 60% daily?

 

[RDuke]

Larry Chanin - what percentage to you personally charge to (presumably every night)?

 

[beeeerock]

View attachment 83124

So someone turned up the temperature in my region the last few days - temps are mid-30's. (95 F). I have no shade at work, so the parking lot is getting above the ideal range for the batteries. This can't be any worse than typical weather in California where the car was designed and built, so I'm wondering about the comments in the image above that state the battery can be cooled.

OK. I've heard the fans running when plugged into a SuperCharger, but I don't *think* I've ever heard them run when plugged in at home or anywhere else. So I'm wondering if the 'cooling' noted above is limited to a radiator system, or is there a heat pump process involved to actively cool the batteries below ambient temperature? Presumably if they can be heated, this might be done with the heat pump, but if connected to 'shore power' as someone called it, perhaps it's just a resistive element. I don't recall seeing this mentioned in the manual but I'll go back into it and look again.

As a test, I've plugged into 110 V here at the office today and I'll go out a few times to see if I hear anything happening. Battery is set for 80% and should be back to that (even on 110) before the heat gets too extreme.

But if someone has an answer on the heat pump question, I'm interested.

 

[Kalud]

I might be a bit crazy, but I charge at 90% and mostly always use the 90%-75% range because its where the power output is at its peak. I feel a good difference between 90% SOC and say 60%.

Now at 28k miles, 90% gives me 231mi and I get 258mi at 100%. I see the degradation as minimal so why get a reduced power car everyday?

 

[chriSharek]

I might be a bit crazy, but I charge at 90% and mostly always use the 90%-75% range because its where the power output is at its peak. I feel a good difference between 90% SOC and say 60%.

Now at 28k miles, 90% gives me 231mi and I get 258mi at 100%. I see the degradation as minimal so why get a reduced power car everyday?

This is a good point. I wasn't remembering that performance declines with SOC. Very good point. cs

 

[Cyclone]

This is a good point. I wasn't remembering that performance declines with SOC. Very good point. cs

Once I get to around 50% SOC, I see power limiting somewhere over 320 kW. The dashed line only ever pops up when I floor it and only kicks in as I get very close to 400 kW. I am well past the 320 kW "notch", so I don't know exactly where its limiting -- maybe 400 kW?!

 

[djp]

But if someone has an answer on the heat pump question, I'm interested.

This thread is a good read on thermal management in the Model S. To directly answer your question, active cooling doesn't kick in until the battery reaches 55C, which isn't likely to happen simply from ambient summer temperatures. The only time the BMS steps in to actively cool the battery is during Supercharging, or if you're spending a day at a track.

Model S Overall Thermal Management

 

[chriSharek]

This thread is a good read on thermal management in the Model S. To directly answer your question, active cooling doesn't kick in until the battery reaches 55C, which isn't likely to happen simply from ambient summer temperatures. The only time the BMS steps in to actively cool the battery is during Supercharging, or if you're spending a day at a track.

Model S Overall Thermal Management

Good link DJP. Thanks for that. BTW, the bow-tie shaped symbols in the drawing are valves.

 

[Drucifer]

Power limiting issues, and the potential of a power failure on the grid has prompted me to move from a planned 70%-40% daily to a 80%-50%. That way, if I skip a day of charging for whatever reason, I will always be at 20% or better.

 

[Kalud]

Once I get to around 50% SOC, I see power limiting somewhere over 320 kW. The dashed line only ever pops up when I floor it and only kicks in as I get very close to 400 kW. I am well past the 320 kW "notch", so I don't know exactly where its limiting -- maybe 400 kW?!

Using the REST API, I see 350-352 kW sustained from a warm battery at 90% SOC and I cannot get much more than 310-320 kW at 50%.

For comparison:
90% SOC: 352kW (472hp)
50% SOC: 310kW (415hp)

So a 57hp is enough, for me, to justify charging at 90% and I don't see real battery range degradation after 18 months.

 

[chriSharek]

Using the REST API, I see 350-352 kW sustained from a warm battery at 90% SOC and I cannot get much more than 310-320 kW at 50%.

For comparison:
90% SOC: 352kW (472hp)
50% SOC: 310kW (415hp)

So a 57hp is enough, for me, to justify charging at 90% and I don't see real battery range degradation after 18 months.

I like this logic!