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What charge rates are you observing?

Discussion in 'Model S: Battery & Charging' started by cinergi, Oct 15, 2012.

  1. cinergi

    cinergi Active Member

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    My Model S is telling me 18 MRPH at 205V 40A which seems really low. Tesla states 31 at 250/40 (240/40?) -- so I should be getting somewhere around 25-26, right? I made sure my HVAC and everything else was off which could slow it down. What are you getting?
     
  2. arg

    arg Member

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    Is this related to the software upgrade that uses EPA range numbers rather than the nominal 300? Or perhaps (as I think you said in your charging video) you have the system set for projected range rather than rated range?

    The 31 stated by Tesla may well be out of date - it is only possible based on 300 miles rated range:

    250V*40A = 10kW. With no charging inefficiencies whatsoever and 300 miles rated range for the 85kWh pack, that gives 300 * 10/85 = 35.3 rated miles per hour charged. If 250/40 was a typo for 240/40 then that would be 33.9. 31/35.3 implies 12% loss in charging; 31/33.9 implies less than 9% loss. 12% sounds more plausible, so my guess is no typo.

    If that was still the calculation, you should be getting 31*205/250=25.4.

    If they are now using the EPA figure of 265 as the capacity, then the figure at 250V becomes 265 * 250 * 40 * 0.88 / 85000 = 27.4 (that .88 is the efficiency).

    On the same basis, your 205V figure should be 265 * 205 * 40 * 0.88 / 85000 = 22.5, so still a bit low.

    If it's using projected range rather than rated, using the figures from your video (projected range 223 = rated range 241) that would give 22.5*223/241 = 20.8. So still not quite right.

    Another possibility is that this relates to the state of charge. Your video shows 18 charge MPH with the car at a fairly high state of charge: the charging efficiency probably varies somewhat with the state of charge (== charger output voltage). It would be a bit surprising for this to be significant, but it would be interesting to check the charge rate when closer to empty.

    A related possibility is that efficiency varies with the input voltage (ie. the rate of charger scales worse-than-linearly with reducing voltage). 250V AC is close to battery voltage (250*sqrt(2) = 353), wheras 205V is quite a bit lower (205*sqrt(2) = 290), so the charger may be operating in a somewhat different mode.
     
  3. donauker

    donauker Member

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    How long are you waiting after charge has started? I have noticed that this number appears to be averaged over some period of time. On my 40 amp 240 volts I will see numbers in the mid 20s that seem to gradually increase over several minutes. If I walk away and come back later I will see the 31 showing.

    I have not yet had a chance to try it on my 208 volt at my office but may have a chance tomorrow.
     
  4. cinergi

    cinergi Active Member

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    Thanks for the thoughtful math arg!

    I sat in the car for about 10 minutes after it hit 18 watching to see if it would go higher ... So you get to 31? Interesting. Hrm ... Next time I see my local service manager I'll talk to him about it ...
     
  5. donauker

    donauker Member

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    I haven't checked any number since I installed the latest software on Sunday evening, but I will record some numbers this evening on 240 volts and tomorrow at the office on 208 volts.
     
  6. donauker

    donauker Member

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    Based on my tests the MPH charge rate is the average of the charge session. So if changing rate or conditions such as car on/off or HVAC on/off you will need to stop and restart the charge to get an accurate number for the new conditions.

    After doing some testing at lower rates I set the rate up to 40 amp with the car showing 212 volts (208 volt service). With 15 min. of charging at 40 amps my MPHC only increased 1 MPH to 16 MPHC. When I stopped and restarted the charge the rate ramped up steadily to 22 MPHC with the car awake but HVAC off. After leaving the car off and locked for 20 minutes the rate showed 24 MPHC.
     
  7. cinergi

    cinergi Active Member

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    Good info, thanks! I'll play with this and report back.
     
  8. cinergi

    cinergi Active Member

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    only saw it get up to 21. I switched the units from miles to energy (now I know what that setting does!) and it shows 8 kW. Unless I measure a long charge by hand and do some math, I'm not sure if I'm actually getting a slower charge than I should or if it's just showing me a really conservative number.
     
  9. donauker

    donauker Member

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    What voltage was showing while charging? I had 212 to 213 showing at the 40 amps.
     
  10. cinergi

    cinergi Active Member

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    I was getting 205/40
     
  11. ElSupreme

    ElSupreme Model S 03182

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    Maybe it is showing projected miles versus ideal miles when you are charging? I think I remember you saying you changed the default display to projected from ideal.

    Just a thought. As 8kW is about right.
     
  12. cinergi

    cinergi Active Member

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    Oh! Good call. I'll switch that and see. Wow. Great memory :smile:
     
  13. cinergi

    cinergi Active Member

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    That was exactly it! Nicely done.

    I have a charging video coming soon which will show this.
     
  14. jcstp

    jcstp Active Member

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    #14 jcstp, Oct 20, 2012
    Last edited by a moderator: Mar 13, 2016


    very interesting
     
  15. Kipernicus

    Kipernicus Model S Res#P1440

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    Do we now have 3 terms regarding miles, ideal, rated, and projected?
    In Cinergi's video at 205V*40A=8kW he showed us 16 projected mph and 20 rated mph, but even if we scaled that up to 9.6kW on a 240V that would only mean about 24mph, not 31 as stated in the Tesla marketing.

    I think the 31 relates to 300 ideal miles, and then rated miles refers to the EPA's 265, and projected refers to how you're really driving and whatever range that implies.
    From what I can tell in the various videos the car doesn't reference 300 ideal miles anymore, which I think is good. Stick with the officially rated figure.
     
  16. cinergi

    cinergi Active Member

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    I don't think so. Donauker has observed 31 (previous post in this thread). You saw me hit 20 only because I didn't wait long enough. If I let it charge longer it will show 24+
     
  17. dsm363

    dsm363 Roadster + Sig Model S

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    #17 dsm363, Oct 20, 2012
    Last edited: Oct 20, 2012
    I believe ideal is now an old term (used on the Roadster) and is equal to rated miles. Estimated=projected miles on the Roadster.

    The first software update I got dropped the rated range from 300 to the EPA 265 which I also think was a very intelligent move. People are likely to come much closer to the 265 mile range than they ever would 300 miles given how most people drive.

    You know, maybe you are right about the ideal miles still being around. Not sure about that now.
     
  18. donauker

    donauker Member

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    Highest I've seen lately is 28 so not sure if this changed with the software update or if voltage made a difference. The 28 was with 240 volts
     
  19. weccman

    weccman Member

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    Well, I've got you all beat for slow charging rate. My utility does not have a very good connection to my house and has been trying to figure out how to improve it. That may change the location of our service drop, so I have not yet put in a NEMA 14-50 circuit because it could be wasted money. I assumed that even at only 5 miles per hour of charging, plus the occasional fill up at a supercharger about 30 miles away, I'd be fine. Well, after I drove home from the factory, I had 121 miles of range left and so I plugged in to a standard 110 wall socket in my garage. I got 3 miles per charging hour, taking about 38 hours to recharge to 240 miles (full on a standard charge). Like the gal said in Chorus Line, "That ain't it, kid." I will really appreciate it when I get over 20 miles of range per hour of charging!
     
  20. ElSupreme

    ElSupreme Model S 03182

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    Are you saying you only have a 60A (Or other small number) feed for your whole house?

    If they upgrade your service to 150A or 200A you would need a new breaker box, but it would cost WAY more to move it than to run the mains feed to the same location as your current breaker location. Running a NEMA 14-50, and new 240VAC circuit wouldn't be a real waste of money (assuming you have room in your current breaker) because it would be easy to move it to a new breaker box.

    Even if you don't have room it would probably be worth while (assuming you will upgrade your service to run the wire and put in the plug and just wait for a new breaker box to terminate in. Or have them run the new circuit when you do the electrical for the service upgrade.
     

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