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Energy lost when charging?

Discussion in 'Model S: Battery & Charging' started by Alexander, Jul 22, 2013.

  1. Alexander

    Alexander P# 8,878

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    Is there any energy loss when charging?

    For example, does it take 95kWh's to fully charge an 85kWh battery?
     
  2. Lloyd

    Lloyd Active Member

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    It has been reported here that the losses when charging are about 10%. Tesla had claimed to be striving to make that number better.
     
  3. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    There may also be a (slightly larger) loss of efficiency at higher amperages than at lower. Don't know if a study to this effect has been done for the Model S yet, but, this is tomsax's blog about the Roadster's charging efficiency at various amperages:

    Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
     
  4. Alexander

    Alexander P# 8,878

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    Awesome, thanks guys!

    I'm trying to calculate the total cost of ownership and I want the charging costs to be as accurate as possible.
     
  5. boilerbots

    boilerbots Member

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    I am attempting to measure this very thing but it isn't easy. If you really want to know the cost you need a power meter on the outlet that the car charges from, don't trust the power reported by the trip stats in the car.
     
  6. X-RAY

    X-RAY Member

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    In saxton's article I can't find a simple percentage ( power from wall / actual power in battery)
    Has anyone measured the energy loss in charging the model s? ( I simply compare the car's data with the certified meter, dedicated to the wall charger )
    I am a bit concerned, for I own a Renault Zoë, where I have measured losses of 25-35%!
    I have not had a response from renault yet. It's like paying for 30 gallons of petrol and only getting 20....
     
  7. mknox

    mknox Well-Known Member

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    I posted something that might be relevant over here.
     
  8. lloyds

    lloyds Member

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    Thanks mknox!
     
  9. viet658

    viet658 Member

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    I'm getting my Model S delivered this week and have a dedicated EV meter so should be able to tell you that information. On my previous car (Chevy Volt), it typically took 12kwh to fill a 10.3 kwh battery so roughly about 16% losses due to charging. I'm surprised that the number I've been hearing on the Model S is almost 30%. That's almost double the Volt's losses. I'll verify once I get the car.
     
  10. gregincal

    gregincal Active Member

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    It's definitely not anywhere near 30%. You need to account for vampire losses, which are constant per day regardless of how much you drive (and hopefully will be eliminated in the future). If you don't drive much the vampire losses swamp other factors. If you drive a lot they are a small part. My charging losses are about 15% + 3kWh vampire loss per day. If I don't drive my car it charges 3kWh at night. For a normal day I use 19kWh, and it takes 22-23 kWh to replace that plus the 3kWh vampire, or 25-26kWh total.
     
  11. viet658

    viet658 Member

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    Wow 3kwh/day in losses? That's pretty significant. My Chevy Volt's vampire losses were almost imperceptible. Average work day (8 hrs) and I would barely even notice a drop in the battery level. Hopefully Tesla works this out. 3 kwh/day adds up to a lot per year.
     
  12. mknox

    mknox Well-Known Member

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    See my data above. In July I was at 29% and I drive about 100 miles a day.
     
  13. montgom626

    montgom626 Active Member

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    10% is a rough estimate of losses.
     
  14. mknox

    mknox Well-Known Member

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    Which losses are you referring to? There are losses associated with the charger, standby (vampire) losses, losses in the battery pack itself, building wiring losses and so forth. 10% certainly can't be all-inclusive when I'm actually measuring 29%. Perhaps just charger losses...
     
  15. montgom626

    montgom626 Active Member

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    Charging only. Vampire loss is a irritation that TMC needs to address.
     
  16. gregincal

    gregincal Active Member

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    I really think unless you separate vampire losses from charging losses the data might be interesting to you personally, but has zero applicability to anybody else. My coworker drives about 5 miles a day and by your method of calculating has a charging efficiency of 10%. Have you calculating your charging efficiency eliminating vampire losses? Because that would be a number that other people could use, whereas the 30% you keep mentioning is misleading because other people will have totally different results depending on how much they drive.

    The other problem with Vampire losses is that Tesla is working to reduce them, so your stat might be applicable for now, but if somebody is looking at the stat figuring out whether to buy the car it will have changed by the time they receive it.

    The title of this thread is "energy lost while charging." Vampire losses don't count.

    - - - Updated - - -

    Another thing to note is that in 4.5 there already is somewhat of a long term sleep mode. If the car is left for more than a couple days I see 5-6kWh used every other day. However, if I have a single days where I don't drive it uses 3.5kWh each day. So when you are driving each day the vampire loss is higher than if you leave the car unused. Certainly the fact that it stops scanning for the keyfob if you have auto-unlock is part of this, but there could be other things they've done.
     
  17. brianman

    brianman Burrito Founder

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    I think you're asking too much of the forum to address this rather than TM. ;)
     
  18. mknox

    mknox Well-Known Member

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    I haven't calculated just charging losses because I don't really have a good way to separate that out. What I'm trying to look at is "power in" (via my meter on the EV circuit) and "power out" as reported by the car's trip meter.

    I hear what you're saying, but "energy lost when charging" says to me this exact metric. In addition to the vampire losses, there are other losses such as standby losses with the battery itself, and in extreme hot or cold, there will be "losses" associated with pack heating/cooling.

    I think it's important to understand this, because at the end of the day what comes out of the wall is what you pay for. Some of that will be to move the car and some will be to cover these losses. This is normal and to be expected with EVs, but I think it's still important to understand, since even if Tesla reduces the standby power to zero, power in/power out will still not be 1.

    To once again flog my ICE analogy, if you spill a bunch of gas every time you fill up, you've still payed for that spillage.

    Since getting my car in early March, I drove it every day (probably averaging 60 to 80 miles/day) except for a 2-week period in July when I was away on vacation. Then, I noticed my car would re-charge to the tune of exactly 5 kWh every other day. I haven't left it unused (other than this time) for more than an overnight period, so I can't say what my daily losses would be.

    Again, no intent on my behalf to deceive or dissuade here, only to educate. I've talked to more than one person who believes what the trip meter reports is exactly how much electricity they've used and paid for, which simply isn't and never will be the case.
     
  19. montgom626

    montgom626 Active Member

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    Unclear what you might be saying. 2 days x 3 kW is 6 and one day at 3.0 kW is 1/2 a two day loss. Are you suggesting an improvement of 1/2 kW per day? I will look, but I have not observed such a subtle difference.

    - - - Updated - - -

    Great analogy. Keep using it. My MS spills 3 kW a day or 12 miles per day. I spill 90 kW per month or 360 miles lost per month. I find the vampire loss to be a big issue for MS to fix. In an ICE getting 20 miles per gallon, it is similar to spilling 18 gallons of fuel per month. No one would tolerate a loss of 18 gallons per month. So why do we accept 90 kW loss per month? My main battery (P85) only holds 85 kW! And there is nothing I can do about it.
     
  20. brianman

    brianman Burrito Founder

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    Technically, you can keep your battery in the self-protection range so that the losses are minimal. But I wouldn't recommend it. ;)
     

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