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Range shorter than EPA (if you want to protect battery)

Discussion in 'Model S: Battery & Charging' started by theaveng, Nov 19, 2013.

  1. theaveng

    theaveng Member

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    I'm an electrical engineer who has owned a hybrid since 2000, and done a lot of research on extending battery life. I've discovered that Lithium-ion batteries don't like to be charged below 20% or above 80% so that limits the useful battery range to 60% of the EPA rating:

    60 kW car: 0.6 times EPA == 125 miles
    85 kW car: 0.6 times EPA == 160 miles

    I would recommend no long distance drivers buy the 60 kW car, and instead buy the maximum capacity battery Tesla sells: 85. Then install superchargers along all the crosscountry interstates (I8, I10, I40, I70, I80, I90, et cetera) at 160 miles minimum, so the batteries can be maintained between 20-80% charge & maximize their lifespan.


     
  2. bluetinc

    bluetinc Member

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    Hi Theaveng,


    Just a couple of questions.

    What exactly are you using for the 20% and 80% numbers? Are you using manufacturer suggested cutoffs of say 2.5V and 4.2V multiplied by your 20%/80%? Are you using 20%/80% of cell voltage or energy storage?

    You can not simply cut 40% from the EPA mileage as Tesla already keeps a significant portion of the battery from the consumer and thus your numbers need to be realigned with the portion of the battery which a user has access to.

    Peter



     
  3. RoverS

    RoverS Banned

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    man. i can't even muster up the energy on a Saturday to replace the towel rack in my bathroom.

    now i has to install superchargers?
     
  4. theaveng

    theaveng Member

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    2.5V is typically defined as 0% and 4.2V as 100%. Charging to those extremes is ill-advised as it shortens battery life.

    I had assumed Tesla used the same definitions, but perhaps I was wrong. I do know Tesla advises "don't charge above 80% unless necessary" as they realize doing so will shorten battery life, and ditto Nissan for their EV, and I agree with both these companies' advice.
     
  5. bluetinc

    bluetinc Member

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    No, Tesla does not use those definitions. Their definitions are significantly inside of those. Also, I don't believe that Tesla has ever said "don't charge above 80% unless necessary", perhaps you are thinking of the 90%+ for "trip" charging?

    Peter

     
  6. drees

    drees Active Member

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  7. ElSupreme

    ElSupreme Model S 03182

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    First 0% on the display is not 0% SoC for the cells, or even the pack as a whole. And 100% on the display is not 100% cell SoC either.

    And Tesla recommends charging to 90% (was 93%) display, which is most likely ~80% cell SoC.

    So I would guess that between 90% display and about 0 miles display is the 20-80% SoC you are throwing out there.
     
  8. liuping

    liuping Active Member

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    I believe there is about 9% non user accessible reserve already included the EPA numbers.

    Also, the battery don't might going to 85% or 90%, they just don't like staying there for long periods. So just have the car finish changing around when you leave for work in the morning and the reduction in range over time will be minimal.

    Having said that, I did order the 85 even though my daily commute to only 40 miles rounds trip. I will be charging to 70% during the week (and end the day 40%) partly to maximize battery life. Weekends and trips will use much more of the range...
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    2.5V and 4.2V is what cell manufacturers define as 0% and 100%; car manufacturers already have an extra buffer built in for their definitions of 0% and 100%.
    For example, for the Roadster, 100% is 4.15V and 0% is 3.00V.
    http://www.teslamotors.com/blog/bit-about-batteries

    As for supercharging and road trips, unless you do it every day, range charging occasionally does not really matter that much. Battery cells are cycle tested at 100%DOD in the first place (using 2.5V and 4.2V cut-offs), so assuming you use up the charge almost immediately, at worse you will get the rated degradation (which is about 70% for 500 full cycles). What matters more is to not keep the battery at high SOC for long periods of time (that reduces the life of batteries the fastest).
     
  10. theaveng

    theaveng Member

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    My advice is the same advice you will find at batteryuniversity's website (just to provide some backing for myself). 20-80% SOC to maximize Li-Ion lifespan.
    So what voltage is used for 0% and 100% on the Model S meter?

    Alo I've read multiple places that Tesla "their advice is for regular usage, never charge it more than 85%." Here's just one link of many: http://www.techspot.com/news/52742-tesla-accelerates-supercharging-station-expansion-plans.html

    - - - Updated - - -

    P.S. If you guys think it is safe I will fill my Tesla (to be delivered in 2014) to 100% and discharge to near-0% during my crosscountry trips, stopping every 250 miles instead of 150 miles.
     
  11. bluetinc

    bluetinc Member

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    Life gets a little complicated when discussing 0% and 100% on the Model S meter because it doesn't give percents such as that directly to the user (though you can guestimate via the fill line one the battery bar).

    Lets say a full charge and use until the range display says 0? If so, then you are talking about 4.15V to 3.3V.

    Your link doesn't include the recommendation you are pointing out. Perhaps you want to go back to Tesla's web site to look for their recommendation? Providing third party links to incorrect information (i.e. new articles) isn't going to give you great facts to use. If it did I would have a car that travels over 400 miles and can be fully charged in 15 minutes according to some articles.

    Peter

     
  12. liuping

    liuping Active Member

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    Planning on going to near 0 is never a good idea, since a change in headwinds, weather conditions, etc can decrease actual range.

    Also, charging at super chargers are very fast at first, but to charge to "full" will take almost twice as long. You are generally going to be better charging to 80% at the SC and stopping more frequently.
     
  13. stopcrazypp

    stopcrazypp Well-Known Member

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    There's nothing unsafe about doing that, but you wouldn't want to do that in the first place because:
    1) it takes much longer to charge to 100% than it does to 90% or something lower
    2) you would leave yourself no range buffer in case you need a detour or have unexpectedly high consumption (like a headwind for example).
     
  14. theaveng

    theaveng Member

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    I tend not to trust manufacturers (or corporations in general). However I've heard the "don't charge above 80% (or 85%) to extend life" multiple times. Tesla, Nissan, Toyota, Honda, Battery University, and also on radio control sites like AMA, et cetera. I don't even charge my iPhone above 80% or discharge below 20%. When the flag pops-up to charge the phone, I immediately put it in airplane mode & turn it off.

    Stopping every 200 miles to supercharge the car along I-80 seems a bit of a pain, but I guess I could get used to it. Probably make my waistline expand too (due to eating at nearby restaurants). ;-)
     
  15. brianman

    brianman Burrito Founder

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    @theaveng
    I get the impression you haven't read this:
    Creating the World’s Best Service and Warranty Program | Blog | Tesla Motors
    In short - just enjoy the car. Unless you're being intentionally brutal to it, Tesla will probably take care of you.
     
  16. liuping

    liuping Active Member

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    You can, assuming the Superchargers are placed in a way that you had the choice, stop every 150ish miles for 20 minutes, or stop every 240ish miles for an hour. I think the shorter 20 minute stops are preferable.
     
  17. Doug_G

    Doug_G Lead Moderator

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    You're linking a COMMENT on a tech blog site? Wow, that's going straight to the source.

    In any case, I don't disagree with the comment. For "regular use", i.e. daily driving, I charge to 80%. It's plenty of range for driving to work, extra errands, driving out of town and back again...

    For road trips I charge to 100% for maximum range. That's the only time I need maximum range. And being at that higher voltage for a few hours has negligible effect on battery lifetime and range. That is why they have the control!

    Also Tesla is conservative about what they call "100%".

    In short, this is completely a non-issue.
     
  18. N4HHE

    N4HHE Member

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    In one message you say you are an electrical engineer and in the above you disprove the claim. Armchair Engineers think voltage is The Unit of Everything Electrical. The first thing one has to beat out of EE freshmen is the notion that everything is volts.

    Capacity of a battery is far from a linear function of voltage. I do not know how Tesla calculates battery SOC for display but if was only a voltmeter then Tesla would be a laughingstock. Temperature greatly affects cell voltage no matter the charge on the cell remains the same. Temperature also affects how much of a charge one can get out of the cell. Then for much of the cell's charge its output voltage is almost constant.

    The most reliable way to display a battery's voltage is to put a power meter on its output and count everything that goes in and everything that comes out. Know the capacity is 85 kWh and you've seen 8.5 kWh come out, so that's 10%.

    I'll reiterate what others are telling you that you are not hearing: Tesla says its an 85 kWh battery. What Tesla is not telling us is what the sum total "industry rated" kWh of cells is used. Is very probably Tesla's 85 kWh is in the very same "industry" 20% to 80% bracket just exactly the same as a Prius 100% charge is only 80% of "industry standard NiMH capacity rating."
     
  19. ChadS

    ChadS Petroleum is for sissies

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    Indeed.

    Using batteries AT ALL degrades them, just like using an ICE wears it out. Charging batteries to "full" (which, as has been pointed out, is not really 100%) degrades them slightly more. But not measurably so. If you're going on a trip and you need it, use it. No big deal at all; and it's been discussed many times on these forums.

    Tesla has been building batteries for years, and they are doing just fine in real life.

    By the way, Tesla already is putting Superchargers in roughly every 90 - 150 miles (they stated 120 was about ideal). So you can easily keep the batteries in the sweet spot if you are really concerned about unmeasurable bits of degradation when you get near the edges.
     
  20. EarlyAdopter

    EarlyAdopter Active Member

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    Batteries degrade whether you use them or not. Storage at high state of charge in high temperatures is what will really take a toll.

    Fortunately, the Model S has a sophisticated thermal management system so this largely isn't a concern.
     

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