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110 vs 240 charging

Discussion in 'Technical' started by bwilliams, Dec 10, 2013.

  1. bwilliams

    bwilliams Member

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    The Tesla charging calculator says that it takes 22.1 kWh to charge for 50 miles using a 110V outlet but only 15.5 kWh using 240 V. kWh should be the amount of energy that is stored in the vehicle - and it is the amount that we pay for. Why and where is the loss by charging with 110V outlet??
     
  2. wycolo

    wycolo Active Member

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    "120 volt charging" be an oxymoron. Should be: "120 volt maintaining" 'cause that's all it is good for. Losses, losses everywhere!!
    --
     
  3. Raffy.Roma

    Raffy.Roma Active Member

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    I suppose that the loss is due to the fact that, since the charging time is greater when you use the 110V outlet, the resistance loss in the wires is greater.
     
  4. captain_zap

    captain_zap Electron tamer

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    Half the voltage input to the charger(s) means twice the current, since the chargers try to maintain constant power. Twice the current means 4 times the losses, since resistive losses are I^2 * R.
     
  5. bwilliams

    bwilliams Member

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    The 120V draws 12 Amps; the 240V draws 40A - more than 3 times the current for the 240V. I^2 * R would mean far more loss with 240V with a constant R. This is not the case ...


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    I'm curious because the 120V was more than adequate for the LEAF and I'm glad, for that vehicle, that I never installed the 240V outlet. In the case of the LEAF 120V charging probably has helped preserve the battery as well. That said, it seems that 120V is not going to fly for the MS.
     
  6. ChadS

    ChadS Petroleum is for sissies

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    HERE is tomsax's old blog on charging rates and efficiency for the Roadster. Note that he only measured efficiency; not what's "best" for the battery. 120V charging definitely is less efficient than 240V charging, although the reasons may (?) have a lot more to do with the car running computers and regulating temperature than resistance.

    A very significant number of Roadster and Leaf owners charge on 120V (I have not seen numbers for Model S). It is definitely possible if you drive less than, say, 40 miles a day...and have reasonably temperate weather. If it's really cold, you may indeed find that 120V is just enough to keep the battery warm, and not get any charge added.
     
  7. Raffy.Roma

    Raffy.Roma Active Member

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    The energy loss is the integral over the time of the power P = V I. In the case of the 120V outlet the numbers for V and I are smaller than the case of the 240 V but the time of integration is much greater I guess. This could be the reason of the greater loss. Than maybe that there is another greater loss in the transformer from AC to DC in the case of the 120 V outlet.

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    As it can be seen in the graph given by Chad also in the case of the Roadster the charge at 240V is more efficient with respect to the charge at 120V. So I happy that in Italy we don't have anymore 120V outlets.
     
  8. montgom626

    montgom626 Active Member

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    I used nothing but 120 volts at 12 amps for 3 months until I got my NEMA 14-50. 120 works fine for charging, even in cold weather.
     
  9. qwk

    qwk Model S P2681

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    Yep, as long as you don't try charging a cold soaked car(it will take forever to warm the pack up to charge it), you will get 3mph out of 120V/12A. That is what I got on FW 5.8 in -8F weather(car outside), which is a huge difference from last winter when sometimes it would only get 0-1mph charging at low temps.
     
  10. derekt75

    derekt75 Member

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    some guesses:

    I imagine it's less efficient to get from 120V AC to the battery voltage (375V DC?) than it is to get from 240V AC to the battery voltage? This might be because it's just harder to get from 120 to 375, or it might be because the charging circuit is probably optimized for 240V so it would be less efficient working at 120V. Also, if the battery needs to be warmed to charge, the longer you charge, the more energy you need to spend in heating.
     
  11. jaanton

    jaanton Roadster NA #1026

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    #11 jaanton, Dec 10, 2013
    Last edited: Dec 10, 2013
    For the Roadster, a circulation pump is running while charging so that represents a fixed power overhead which comes from the supply. I don't know off the top of my head how much power that is, but say it's 200 W. You're getting 1650 W from the 110v at 15A, then you subtract the 200W from the pump/overhead and you're left with 1450W for charging. If you're charging at 110v at 12 A that's 1320 W minus 200 W then you're left with 1120 W. If you're charging at 240V at 40 A that's 9600 W charging at 9400 W.
    Overhead percentage is then 12%, 16%, and 2% respectively. Other overheads such as efficiency of power conversion are probably involved.
     
  12. stopcrazypp

    stopcrazypp Well-Known Member

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    That illustrates quite nicely the issue with 110V: fixed overhead costs are high relative to the charge you are getting. And whatever additional resistive losses you are getting from high current (which you can avoid by dialing down your 220V charging current) is probably less than the overhead.

    This seems to be true even for the Leaf (even though the battery does not have thermal management, the charger does).
    http://www.mynissanleaf.com/viewtopic.php?f=31&t=8583
     
  13. bwilliams

    bwilliams Member

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    Thanks for the info, folks. I hadn't realized the extent of overhead.
     
  14. montgom626

    montgom626 Active Member

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    I got 2 mph at 10 amps on 120 volts in 5 degree Fahrenheit outdoors.
     
  15. qwk

    qwk Model S P2681

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    Was the regen limited at all when you started charging?
     
  16. montgom626

    montgom626 Active Member

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    Yes.
     
  17. wycolo

    wycolo Active Member

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    > I got 2 mph at 10 amps on 120 volts in 5 degree Fahrenheit outdoors. [montgom626]

    So 16 hours later (the next morning) you have all of 32 miles to spend that day. Kind of a Leafy existence fer sure. In the summer that would be 48 miles so likely 85% of drivers would be satisfied. But if you face a 170 mile round trip the MS won't be ready until the 3rd day barely. When I first got the Roadster I only had 120v charging and the car would be just marginally charged 2 days later for this trip; much safer to wait until the 3rd day. Luckily the MS has always had [email protected] available at home.

    In an emergency 120 volt charging for the MS is essentially useless. Rather than plug in and kill time to gain the 2 or 3 mph, it is much quicker to simply drive home slower, even MUCH slower if need be. Thus I've never used the UMC on 120v but it is always in the trunk.
    --
     
  18. montgom626

    montgom626 Active Member

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    Yes. And a "warmer" battery. In Midwest cold weather, when visiting friends overnight, 120 volt outlet is a lifesaver. More miles, warmer battery. All of this is good. If I had not plugged into the 120V, I would 40+ miles in the minus column.

    As it was, I was plugged in for about 24 hours, had 48 extra miles and a warmer battery.
     
  19. Crispix

    Crispix Member

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    I just charged mine from 26 miles to 90% over a 48-hour period at ~112v/12amps. Temp was in the low 40's, Las Vegas/Venetian garage. App reported a consisted 4mph charge rate.
     
  20. green1

    green1 Active Member

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    I know this is an old thread, but I thought it might be better to post here than to create another similar thread.

    I have a bit of a trip coming up that could cause me some pain. I'm heading to a place in the middle of nowhere, in January, in Canada. The closest supercharger is too far away to make the round trip, and the only one I can find on plugshare between the two is in an inconvenient spot, only 9kw, and without additional charging I'd need to stop there both ways, I'd like to avoid that if possible.
    I'm not expecting any 240v charging at the destination (though I do have an email in to them with some wishful thinking) I suspect they'll only have 110v available (even that is not guaranteed, and if they don't I won't have much choice but to use the ICE)

    I have calculated, with some help from EV trip planner, that I need to achieve an absolute minimum of 3km/hr (1.8miles/hr) of charge while I'm there to reach the supercharger on the way home (not counting any losses while parked, could be relevant?)
    I'm expecting temperatures in the range of -15 to -20 c (5 to -5 F) though it could dip colder at night.
    I'll start with a warm battery from a long drive, but will be charging for 2 days so not sure how warm the battery will stay

    I know those rates of charge would be quite doable in the summer, but I'm worried in the cold it might be different.

    Am I crazy to attempt this? or does this seem reasonable on a 110v outlet? Really don't want to take the ICE if I can avoid it, the Tesla is just so much nicer, especially on road trips!
     

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