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Charging on NEMA 5-20 at 7mph!

Discussion in 'Model 3: Battery & Charging' started by fiatlux, Aug 9, 2018.

  1. fiatlux

    fiatlux Member

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    Hi TMC,
    TLDR: Charging now starts at 6mph and a reaches a steady 7mph on NEMA 5-20!

    Details, AKA why would anyone do this instead of a 14-50?
    * I don't drive much -- approx 150mi/week
    * It should be slightly more efficient (about 1/4 less time charging == less charger overhead)
    * On a NEMA 5-15 I was seeing 5mph. Plenty for my needs, but the 5-20 adds margin both for range and weather (preconditioning etc).
    * Our electrical panel was totally full, except for a well situated 20amp circuit (on a single pole breaker).

    For anyone debating what to do but with similar low-range needs, I'm pretty happy with the 5-20 :)
    Cheers!

    IMG_8936.PNG
     
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  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Well-Known Member

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    I've mentioned this before, but counter-intuitively long-range BEVs make it _easier_ to live with low-power charging and you're an example.

    If _on average_ you can charge more miles at home/destinations than you use, then you'll end up with a full battery. So the only problem would be if your usage pattern empties your battery as some point. With long-range you have a larger buffer that makes it less likely that your regular routine would empty your battery.
     
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  3. nwdiver

    nwdiver Active Member

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    16A might be slightly more efficient than 12A but 240v is ~10% more efficient than 120v. You could repurpose your N as a L and upgrade your 120v outlet to 240v with a NEMA 6-20. Double your charge rate AND increase your efficiency.... The full panel problem can probably be solved with tandem breakers.
     
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  4. Cosmacelf

    Cosmacelf Well-Known Member

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    Be careful about converting a 120v outlet to 240v unless you KNOW that only one receptacle is on that circuit. Usually 120V circuits have several receptacles daisy chained together.

    There is nothing wrong with 120V, 20A charging. I did it for quite a while with my Model S. Worked great.
     
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  5. nwdiver

    nwdiver Active Member

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    Your charging outlet should be dedicated anyway since the car is using the entire continuous capacity of the circuit. Upgrading from 120v to 240v would cost ~$50... that's <2 year payback in energy savings alone for typical use...

    Depends on what you mean by 'nothing wrong with'... maybe in the same vein as 'nothing wrong with' a 40 year old living with their parents... sure... but it's not ideal and should probably be fixed for multiple reasons....
     
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  6. Cosmacelf

    Cosmacelf Well-Known Member

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    I disagree. I’ll leave it at that.
     
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  7. yuhong

    yuhong Member

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    I wonder if you have only 100A service.
     
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  8. ratsbew

    ratsbew Member

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    I upgraded a 5-20 to a 6-20 for $15 in parts. I get a steady 15mph of charging. It works great!
     
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  9. Rockster

    Rockster Active Member

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    We charge on a 5-20 when we visit the in-laws and it works fine for us.
     
  10. SigNC

    SigNC Member

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    I charge on a 5-20. It's about 6.5mph but the tesla app will round up. If you look at it in remote S you will see it lands around 6.5 and from what I can tell it really is a little less than that because charging times are always a little longer than what remote S estimates. Either way, the 5-20 has been fine for me but I'll probably end up getting a nice 240 circuit at some point just for those rare times when I need a quicker turn around.
     
  11. nwdiver

    nwdiver Active Member

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    Sure... probably better than nothing in a pinch. But if you're low and need a full charge overnight that ain't gonna happen and if it's <20F your car may not charge at all since the heater will use ~1kW just to keep the pack warm enough to accept a charge. Before we got L2 at work I used a 120v outlet to charge at 16A.... better than nothing but not a real solution. The energy savings alone are worth the upgrade.
     
  12. Rocky_H

    Rocky_H Active Member

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    You're misinforming people by saying that voltage changes have more efficiency impact than amperage changes. The charging speed and efficiency of charging of the car is based on power, which is the product of volts times amps. So increasing either one, which gives more power, is what helps efficiency.
     
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  13. nwdiver

    nwdiver Active Member

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    #13 nwdiver, Aug 10, 2018
    Last edited: Aug 10, 2018
    The voltage plays a role in the efficiency of charging. The AC voltage needs to be converted to ~300 - 400v DC. The higher the AC voltage the 'easier' this is. There are a lot of factors involved that effect the overall efficiency but the most common number I've seen is a ~10% difference. L2 is generally ~10% more efficient than L1. Losses are also based on current not power this is why transmission lines use high voltage (lower current). Line losses for 1.2kW are 4x more with 120v than 240v since current needs to be twice as high with 120 vs 240 for equal power and the equation for line losses is AMPS^2 X Resistance.

    So between needing ~2x as much current for the same power level plus the fact AC-DC conversion to ~350vdc is more efficient with 240 vs 120... ~240 uses on average ~10% less energy per mile of charge.

    Here's a study examining this.... L1 is almost always <2kW and L2 is almost always >2kW so from this study the difference would be ~71% vs ~86% or ~15% more efficient for L2.

    Screen Shot 2018-08-10 at 4.18.53 PM.png
     
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  14. BestHand

    BestHand Member

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    fiatlux I think I will drive even less (I only made about 11K on my 12 years old Honda, which is less than 1K a year), but I still will install NEMA 14-50. It will put my mind at ease. Also, If you will use 120V circuit not dedicated for charging only (same circuit may have more than one receptacles) it can be cases that breaker will break and charging stopped. And the same as you I have only one slot available in my electrical box, so I will use tandem breaker to make two slots available.
     
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  15. Electric700

    Electric700 Active Member

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    +1

    I have a 6-20 too (Gen 2 Mobile Connector + the Tesla 6-20 adapter) and am really liking charging at 240 V!
     
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  16. davewill

    davewill Member

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    Exactly. Increased efficiency in this case comes from the fact that there's a fixed overhead to run the cooling pumps and the like. Any added power over 120v 12a is going directly to charging the car, increasing the efficiency of the entire process. While there may be a conversion efficiency pickup from 240v over 120v the real pickup adding power that isn't being mostly used for overhead.
     
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  17. BestHand

    BestHand Member

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    If we assume that cooling pumps work the same with 120V or 240V charges, then of course, less time you spent on charging, less time you spent on pumps working. From other sede, I do not know if cooling pump needed when you charge slowly with 120V, I assume there is some temperature sensor. Generally it is a big area to research.
     
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  18. aydyn

    aydyn Member

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    What on earth are you talking about? Electrical 101, 240v is ~10% more efficient then 120. This has nothing to do with the battery cooling or “overhead” it is less power lost in transmit (ie heat). You should not use 110 to charge a tesla, it is wasteful and there is no reason for it.
     
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  19. TexasEV

    TexasEV Well-Known Member

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    You’re both right.
     
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  20. Rocky_H

    Rocky_H Active Member

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    Oh really? Try this one:
    120V at 30A = 3,600W
    240V at 5A = 1,200W
    You are saying that the second one is 10% more efficient. Most would disagree with you, including, you know, science.
     
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