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Home charging

Discussion in 'Model S: Battery & Charging' started by D.E., Mar 29, 2018.

  1. D.E.

    D.E. Uncorked

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    I don't drive much. When charging at home I use a 120v 15A outlet and the car charges at about 4 miles per hour of charging.

    I know the power use is less efficient this way, there is power use due to pumps and other various systems so a smaller percentage of the supplied current actually winds up charging the cells. How much less efficient is it?

    Is there any advantage to the Tesla wall charger beyond an increase in charging efficiency? I can get fairly close to the efficiency using a 240V 50A outlet and the supplied cord, allowing me to charge at 40A, not the 48A I'd get with the charger.

    If 4 miles of range for each hour of charge is enough for me, is there a down side to charging at 120V? That is just under 100 miles per 24 hours which is plenty. Is it harder on the car?

    I can install a 240V 50A outlet fairly easily. Is there any reason to put in a Tesla charger vs a 50A wall outlet?

    I live 2 miles from a supercharger so if I need a quicker charge, it is available.
     
  2. steve841

    steve841 Active Member

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    IMO ... efficiency is pennies and not worth the thought.

    Time: There's gonna be that one time when you're gonna need a quick refill and kick yourself for not adding some kind of high amp outlet.
     
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  3. brkaus

    brkaus Well-Known Member

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    I’d say no significant efficiency difference between HPWC and 14-50 outlet.

    I see your in the cold, 120v won’t help much (if any) if the pack is chilled. Even the Supercharger is slow if the pack is cold soaked. I think you may want more at home in the winter.

    120v will have pumps and such running longer. But will not generate as much heat. No idea how to balance the two in terms of “best for the car”.
     
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  4. SSonnentag

    SSonnentag Rocket Scientist

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    My calculations show:
    120V AC at 85-86% efficient.
    240V AC at 89-91% efficient.
    Supercharging shows up as 97-98% efficient.


    ** Measurements taken with ambient temperatures between 45 and 65 degrees F. All charges have been on a warm battery following 175 miles of highway driving.
     
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  5. Qbenjamin

    Qbenjamin Frugal But Classy!

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    I slow charged regularly when I moved and didn't have my NEMA 14-50. Considering I was only putting around 8 miles per day on the car, the desire to charge at a faster rate just didn't matter to me anymore.
     
  6. SSonnentag

    SSonnentag Rocket Scientist

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    Figure an additional $20 USD for every 10,000 miles worth of charging on 120V.
     
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  7. D.E.

    D.E. Uncorked

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    I am in the cold but the car is garaged so it isn't quite as bad. I also have other cars, they well used. I don't tend to drive the Tesla in the snow, the salt, or down our dirt road when it is muddy. I'm old so this car will probably see me through, I'd like to keep it as new as I can for as long as I can.
     
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  8. D.E.

    D.E. Uncorked

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    Mmm, so using your figures and doing the math, the breakeven for buying the $500 Tesla charger is somewhere in the neighborhood of a quarter of a million miles. That's the distance to the Moon. I don't think I am going to drive it that far.
     
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  9. SSonnentag

    SSonnentag Rocket Scientist

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    Yep. You don't want a level 2 charger to save money. Its benefit is quicker charging and preconditioning that actually works in a timely fashion and doesn't drain the battery. :D
     
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  10. FlyinLow

    FlyinLow Enjoy the journey

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    Same for us. The quotes to run the wire for a NEMA 14-50 the length of our house to get to the garage is prohibitive. At $1500 to $2000 it just isn't worth it.

    I'm thinking about trying a "Quick 220" for about $200 to get the charge rate up to a level that will easily handle the winter, allow me to pre-heat the car easily and can help with bumping up the charge if I decide I need to add some miles to the car for the next day. I have to check my garage to see if I have two circuits that aren't on GFIs and on separate breakers.

    Stopping off at a close by super charger is a great option, I have three, North, South, and East of me, all about 30 miles away. Starting a trip I can just go and hit one of those on the way out of town for a longer road trip.

    As well as I plan there may be a time I just would rather not take that time to charge when I could have done it at home. At above 60% my S85 charges a lot slower at SuCs than at the bottom half of the battery too, so it isn't always a quick top up to 90% before I start my trip.
     
  11. Emcsquared

    Emcsquared Member

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    I was charging at my apartment at 120v for a few months, finally purchased a house and installed a NEMA 14-50 and I use the included mobile charge cable, charging at 40A and that is more than enough for me. I have thought about the HPWC due to cleaner appearance but not worth it IMHO. The 14-50 was an amazing upgrade.
     
    • Informative x 1
  12. brkaus

    brkaus Well-Known Member

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    I’d personally see how much it would cost to have a 14-50 installed. Under $500 I’d just do it for th convenience. Over - I’d sit on it and see how it goes.
     
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  13. GatorGuy

    GatorGuy Member

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    Since you don't drive much and have other vehicles it sounds like you don't have need of anything faster than 120V.

    One thing everyone should check on though is rebates from their power company. Mine gave me a $1000 rebate for installing a level 2 charger. So it paid for the HPWC and 100 amp installation.
     
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  14. lymex2018

    lymex2018 Member

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    The on-board charger works more efficiently when the power is large, say 50% to 90% of full power. Although the charger in a 75D is not the high-power one, but 11kW? 120V and 15A is 1.8kW max, which is 16% of the full power, and the efficiency of converting this AC to high voltage DC is smaller than the ideal condition.
     
  15. D.E.

    D.E. Uncorked

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    Then I'll plan to install a 50A 240V plug and use the factory cord.
     
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  16. UberEV1

    UberEV1 Member

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    Another consideration if you are on a Time of Use (ToU) electricity plan . . . depending on how many miles one drives, re-charging with 120V may span both peak and off-peak time periods (thus driving up average cost of electricity). Using the 14-50 gives you more flexibility to ensure your electricity consumption is only during the cheaper off-peak hours.
     
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  17. Rocky_H

    Rocky_H Well-Known Member

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    You're probably not going to be able to find that in any of your garage outlets. By building codes, the garage outlets need to be GFCI because they are considered to be too close to water exposure, like water heater, etc. So you would end up needing to run extension cords from two outlets inside your house out into the garage, which is a pretty crummy situation.
     
    • Informative x 1
  18. Snipealot

    Snipealot Member

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    I lucked up and my washer/dryer room is located on the same level as my garage and I have a 10-30 outlet for my dryer so I purchased a 10-30 extension cord and the Tesla 10-30P adapter for my UMC and that gives me 22 miles/hour of charge.
     
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  19. BlueRocket

    BlueRocket S90D HW3.0 upgrade MCU1 "FSD" 2020.24.6.11

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    I've been charging at 120v 12amps for 15 months now (just too lazy to install another line) . Like the OP, I don't drive that much and getting 50 miles overnight is adequate. I do go on a fair number of long trips so I supercharge a good percentage of the time. I plan to install a wall charger on a 50 amp line since I chose that for my second referral code.

    As far as battery health goes, I have about 12,000 miles on the car and have lost only 1-2 miles of range. I charge to 80% unless I'm planning on a trip, then I will charge to 100%. Winter charging not an issue but the car is garage kept where the temperature never goes below 35F.
     
  20. Chaserr

    Chaserr Hyperactive Hyperdrive

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    The garage door outlet on the ceiling is almost never GFCI, those can be used most of the time if you need normal outlets in the garage.
     
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