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Charging 120v vs 240v efficiency

Discussion in 'Model 3: Battery & Charging' started by wesley888, Aug 15, 2018.

  1. wesley888

    wesley888 Member

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    The model 3 is going to be our secondary car and will only get driven a couple of times a week for just a few miles. So charging speed is not an issue at all. I'm wondering if charging at 120V is less efficient than charging at 240V. Any idea?
     
  2. TexasEV

    TexasEV Well-Known Member

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    Yes. Search for lots of threads on this already.
     
  3. Kermee

    Kermee It's Not Easy Being Green

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    Short answer to your question is yes, 120V is less efficient than charging at 240V. However since you've stated that you're only driving a couple of times a week for just a few miles, the difference in costs due to the delta in efficiency may be negligible.
     
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  4. gambit48

    gambit48 Member

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    My opinion is that unless your electrical panel is really far from the garage and costs would be really high, the convenience of being able to charge fast outweighs the small one time cost to put in a 240v outlet. My parents have 3 cars and two drivers. They thought they could get away with just the 120v as well. A couple of unexpected events happened (one of which was me visiting with my Model 3) and the hassle of only having a 120v outlet convinced them to just add in a 240v even if it would be rarely used. Now, they use it a lot more than they thought just for convenience sake of having the car always topped up to 80%.
     
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  5. ewoodrick

    ewoodrick Member

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    Efficiency isn't a great word to explain the difference here. They are both just as efficient.
    But, they don't charge at the same rate for two reasons, When the cars is being charged, a percentage is used to maintain the car and the remainder used to charge the battery. Since the charge rate is lower for a 120V the percent of power going is lower.

    120V @ 12A is 1440 watts
    If it was 240V @ 12A it would be 2880 watts.

    If 120V charging is good enough, then it is indeed good enough. If it is a double 120V 15A plug, then standard type, that can probably be replaced with a single 120V 20A plug and you can get the correct Tesla adapter and charge at a little faster rate for very little investment.
     
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  6. eprosenx

    eprosenx Member

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    I think there are a couple of factors here: Speed and efficiency. They are linked to a large degree.

    When charging the car, it wants the battery to be at a specified temperature range and I believe it runs the cooling pump continuously during the charging as well. So when you are charging there are certain fixed charging losses. Let's just say they are 400 watts (totally made up #). So charging off 120v @12 amps means you are only getting 1440 watts minus the fixed 400 watt overhead is 1040 watts. But if you are charging at 240v @ 12 amps you are at 2480 watts. That is nearly 2.5 times as fast.

    Also, on the pure efficiency level- A 240v rectifier is going to be slightly more efficient than a 120v rectifier. This is one of the reasons we run all of our datacenters at 208v vs 120v.

    From my standpoint, the less time the cooling pump and such is running perhaps the longer life you will get out of it (though this has to be balanced against other factors like if you run things at some fraction of their rated capacity it is often times better for them).

    I charge my model 3 at 48 amps 240v every day as soon as I get home just because I can. There are no time of use provisions that make it cheaper to charge later, and I have a very robust electrical service that can trivially handle it. In the event I needed to go out in an emergency for any reason it is nice just knowing the car will be at 80% within about an hour of me getting home (that is what I set my limit to).

    Now if someone can provide evidence that charging slower than 48a is better for my battery then I will modify my behavior, however, 11.5kW is so vastly slower than a supercharger that I suspect it can handle it trivially.

    I don't ever want to be limited by my car not having enough charge, and I don't want to have to juggle car charging every day.

    To the comment about being able to upgrade from a 120v 15a receptacle to a 120v 20a receptacle: Yes, this is very often doable in garages but not always!!! I did this in my garage, but you need to check that you have 12 gauge copper wiring and a 20a breaker. If not, this could be dangerous. But yes, that extra 33% (going from 12a to 16a charge rate) is huge. Due to those fixed losses during charging it makes a huge difference. I actually have a "cheater" adapter that lets me plug my 5-20 Tesla UMC adapter into a 15a receptacle. Note that this could be very dangerous, but I have only used it once when I 100% confirmed that the receptacle I was using was on a 20a circuit and it was the only plug on it and it was only a few feet from the subpanel. This still does not mean the 15a receptacle was rated for 20a, though it worked completely fine and did not get hot at all. I would never use this adapter at home, I would always wire in the right receptacle instead.
     
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  7. TheLocNar

    TheLocNar Member

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    Once you get the car it won’t be driven just a few mikes here and there. I’d consider getting a NEMA plug installed.
     
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  8. TexasEV

    TexasEV Well-Known Member

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    I think you mean a NEMA 14-50. Every plug in the US is a “ NEMA plug”. That’s like saying something weighs pounds without saying how many. Household outlets are NEMA 5-15 outlets, etc.
    http://www.trci.net/media/4682/nemaplugreceptacleconfigurations.pdf
     
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  9. Rocky_H

    Rocky_H Active Member

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    Thank you--this bugs me as well. How many metrics is it from Austin to San Antonio? No--"metrics" isn't a unit--it's the name for the whole system of units.
     
  10. TheLocNar

    TheLocNar Member

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    Yes. I’m aware. He could get a NEMA 14-50 or lesser. I was being general. :)
     
  11. Darmie

    Darmie Supporting Member

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    We have done 110 charging at our apartment for approx 1 year until the S sold. So, it works great for us. you usually can get approx 40 to 50 miles in the car a night. My wife's comute is under 25 or so a day. On hotter days, the car will consume more range miles that that however it has worked out great. I tell ya what I really like about 110 charging. i'm always hovering around the 50% area of the battery. On weekends, we are at a S/C . The Efficiency as you speak of was mention above and I agree, it's all about the time vs charge. With the 3 you may get more miles per hour than the S. Now we have ordered the X, I'm wondering if 110 will work out for us since it's a much hungry car.
     
  12. aydyn

    aydyn Member

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    They ar
    They are NOT the same efficiency, 208/240 is ~10% more efficient as I. Less power lost in transmit (heat) then 110/120
     
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  13. MXWing

    MXWing Active Member

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    Paging @Jedi2155

    He will close the thread. ;)
     
  14. Jedi2155

    Jedi2155 Please Insert a Model 3 into Avatar

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    You have too much confidence in me lol. I'm sure others have done a more thorough analysis than what I plan on typing here.

    The efficiency between 120v/240v is likely similar but the losses with 120v is significantly greater. The charging efficiency refers to the actual conversion efficiency between AC and DC and both could be > 90% (240v is usually greater by a small amount).

    The important to thing to understand is there will be a constant power draw from other systems while you are charging that is not insignificant (all those extra computers that can't go to sleep while charging for example.) which can amount to 300-600 watts. Lets call this system losses assume 540w in this example.

    So if you're charging at:
    120v / 1440w - 540w loss = 900w is available to go in the battery in 1 hour.
    This means only 900/1440 = 62.5% of the available power goes to the battery.

    When the available power goes up, those constant system loss stays the same and charging efficiency usually increases too based on a curve. So using the same example above assuming same efficiency we get this example:

    So at:
    240v / 2880w - 540w loss = 2340w is available to go in the battery in 1 hour.
    This means only 2340/2880 = 81.25% of the available power goes to the battery.

    Now this number increases up to a particular point where the charging efficiency starts dropping and being a bigger impact than the system loss. There was another thread where an individual determined that 25-30A @ 240v seems to be peak efficiency. Far below the max 48A input capacity of the Model 3 LR, but still reasonably fast. The overall efficiencies at those points is between 88 to 97% efficient.
     
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