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Charging a Model X at 240v 16 amps vs 32 amps

Discussion in 'Charging Standards and Infrastructure' started by RVD98072, Dec 3, 2017.

  1. RVD98072

    RVD98072 Member

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    I have a L6-20 outlet in my garage so I was using my UMC to charge with that. The only problem is that it only charges at 240v 16 amps on the 20 amp circuit.

    Last night I installed a Tesla hpwc on a 40 amp circuit so it charges at 240v 32 amps.

    However, when I charged this morning, it seems only slightly faster. On 240v 16 amps, it said that I can charge at 10 miles/hr. On 240v 32 amps, it says that I can charge at 12 miles/hr so the time savings is not much.

    Does this sound right?

    Screenshot_20171203-080945.png
    Screenshot_20171203-085901.png
     
  2. Big Earl

    Big Earl Member

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    It can take several minutes for the miles per hour display to catch up to your actual charge speed. If you took that picture shortly after you plugged in, it probably wasn’t accurate.
     
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  3. AZ Desert Driver

    AZ Desert Driver Rare combination

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    And you have all night to charge - so why cram it in fast? Yes the equipment can handle it, but why stress the gear/heat the cables,/run the battery a/c....why do that when you are not in a hurry?
     
  4. RVD98072

    RVD98072 Member

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    I ran a few more tests and I think it was the combination of:

    1) I waited about 3 minutes to take that picture but it still was too early
    2) I was in the car when I took that picture so the car was on, climate control on, etc.

    I am charging right now and waited about 10 minutes, left the car, etc. and it's showing a rate of around 20 miles/hr which is what I expect so I think we're good.

    As for cramming it in so fast, it's not uncommon for me to get home at around midnight and then leave at around 7am the next morning so it'd be nice to be able to charge around 150 miles/night instead of 70 miles/night. I can usually charge a bit during the day as well. This isn't every day but it's common enough that it comes in handy.

    The hpwc can charge up to 80 amps I think (and my car supports up to 72 amps) but I don't need anywhere near that fast so I think 40 amps is plenty for me. It will also take a bit of work to get that much capacity in my home (I think I have 200 amps coming in now).
     
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  5. Rocky_H

    Rocky_H Active Member

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    As mentioned previously, the miles per hour number is a long term average of the charging session, not an instantaneous reading, so it gets kind of weird sometimes or reads low because of some slow startup time.
    I think the person's comment was a little confusing there:
    "Yes the equipment can handle it, but why stress the gear/heat the cables,/run the battery a/c"

    Some of that is legit(ish) and some not. The "run the battery a/c" part is kind of nonsense. For home charging on 240V, it's never making enough heat that it's having to run the A/C to cool itself. And run the battery? It's having to be connected to charge anyway, no matter what speed, so that doesn't really make any sense either.

    The part that kind of is relevant is stress/heat in the charging cable. The mobile connector running at its maximum rating of 40A frequently does get kind of hot at that level, and heat is the main factor in degrading the lifetime of electronics, solder joints, etc. That's especially true of heat cycling, where it's going from hot to cold and back frequently, like in this daily charging situation. So the recommendation he's getting at is that if you can run maybe low to mid 30's amps or so, you get most of the charging speed benefit, but it stays noticeably cooler, and will probably extend the life of the charging cable.
     
  6. Canuck

    Canuck Well-Known Member

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    I don't view 32 amps as cramming it in fast. I dial down my dual 40 amp chargers to 42 amps, so each charger uses 21 amps, and I find 42 amps slow but fine for overnight, and I can always dial it up if more is needed. The OP can always dial down if he wants, but he can't dial up until he fixes the problem.

    That doesn't sound right to me. The cart below is from the Canadian Tesla site so it's in km but you can see that the difference between 15 and 30 amps is 8 and 23 km per hour for a Model X:

    Connector power options
    Wall Connector circuit breaker options Mobile Connector outlet adapters Max power (kW) at 240 volts Estimated recharging speed,
    kilometers per hour
    Model X / Model S
    100 amps ** N/A 19.2 kW 72 / 84
    90 amps* N/A 17.3 kW 72 / 84
    80 amps* N/A 15.4 kW 64 / 74
    70 amps* N/A 13.4 kW 56 / 64
    60 amps N/A 11.5 kW 48 / 55
    50 amps N/A 9.6 kW 40 / 46
    45 amps N/A 8.6 kW 37 / 42
    40 amps NEMA 14-50 7.7 kW 32 / 37
    35 amps N/A 6.7 kW 27 / 32
    30 amps NEMA 14-30 5.7 kW 23 / 27
    25 amps N/A 4.8 kW 18 / 23
    20 amps N/A 3.8 kW 13 / 18
    15 amps N/A 2.8 kW 8 / 11
     
  7. hpjtv

    hpjtv Member

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    #7 hpjtv, Dec 10, 2017 at 2:11 AM
    Last edited: Dec 10, 2017 at 2:58 AM
    Those numbers don't seem right. 15A to 30A is twice as much power, look at the kW. Why is the 100A and 90A the same? If you look at 40A to 80A, it doubles. I charge at 12A (just because I can) and get 13km which is more than the 11km they say for 15A. Whoever wrote the manual screwed up. Also, those are breaker ratings, not actual current to vehicle which is 80% of the rating.
     
  8. hpjtv

    hpjtv Member

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    #8 hpjtv, Dec 10, 2017 at 2:41 AM
    Last edited: Dec 10, 2017 at 2:50 AM
    Just looked at the US website, from 20A to 40A, everything doubles, from 30A to 60A, doubles. Looks like there's lots of rounding going on here on top of the miles to km conversation.
    Home charging installation
    And I believe RVD98072 already answered his question. He was getting 10miles/hr at 15A and 20miles/hr at 30A after waiting for the screen to update.
     
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  9. Rocky_H

    Rocky_H Active Member

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    There are a few things you're not getting about this, and no, it's not that someone screwed up when writing this.
    The 100A and 90A breakers are listed as the same because the cars now only include up to a 72A charger onboard. A 90A breaker will support that, but the car can't take any more power even if it's installed on a 100A circuit.
    And the scaling up being more than double is about greater efficiency at higher power levels to overcome the energy that is lost running the charging circuit. There is somewhere around 300-400W lost just for running the onboard charger while it's active. So when you are going up from a very low power level (where a high % of the power is not going toward energy going into the battery) to a higher power level, then yes, it really does work out to be more than just what the increased amps would show, because all of the overhead losses are accounted for already, and the extra is ALL going into the battery. Once you're talking about increases from 40, 60, 72, etc., though, the power levels are high enough that 300W or so of losses barely show, so it does scale almost directly with the amps.
     
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