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EV ChAmp app is fantastic -- will use it from now on

Discussion in 'Model S: Battery & Charging' started by artsci, Jan 24, 2017.

  1. artsci

    artsci Sponsor

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    I downloaded the new EV ChAmp app a few days ago and used it for the first time last night.

    It calculates the charging amperage necessary to have your car fully charged by the time you want to leave in the morning (or other time). You enter the start time and start range as well as the end time and range desired and it calculates the amperage necessary to have the car charged to your desired level by the specified time.

    I entered a start time of 9pm (when my electric rates drop) and a starting range of 64 miles. It indicated I should set the charging amperage to 18 in order to have the car charged to a range of 180 miles by 8am. It's now 7:45 am and the car is charged to 179 miles. So it's incredibly accurate.

    This is a great app and it enables something that many of us thought should be a built-feature. This app should be especially helpful when I want to do a full charge for a long trip but not let the battery sit fully charged for very long. In fact, I have a long trip tomorrow and will try it out. I'll set the desired range to 260 miles with a departure time of 9am.
     
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  2. meloccom

    meloccom Moderator Aus/NZ

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    It doesn't seem to work for cars running in metric.
     
  3. docherf

    docherf Member

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    That's a good idea. I will try this when I charge to 100 before a trip. It would be great if it could adjust the amps remotely.

    Also, I have gotten used to having the car displaying percentage. I guess using percent instead of miles in the app would also make the app need to know what specific model your car is.

     
  4. BerTX

    BerTX Active Member

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    Just be careful the next time you do a regular charge -- the car will remember the rate you set before and charge at that rate again at that location. You may not get fully charged in the time allocated.

    Also, as I recall, you waste more electricity charging at a lower rate.
     
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  5. scaesare

    scaesare Well-Known Member

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    That's cool, but what I'd really like is an app that will calculate this and then use the REST API to trigger charge events for me.

    While adjusting the charging current might be useful in some circumstances, the API doesn't seem to allow for that, but you should be able to hit a desired end time without having to adjust current by simply adjusting the start time.

    Visible Tesla demonstrates that all the needed info is there: the car can report via the API what the voltage and pilot current values are. Based on that you can determine approximate charge rate. Then simply do the math to calculate when to send a charge_start event.

    To make things even more accurate, you could use the car's reported temperature to calculate some adjustment factor. You could also use the cars reported location coordinates along with historical data to approximate expected voltage drop to help tune over time. (the drop at my work location is much worse than at my home location). Finally, if the app also manages HVAC start events (as Visible Tesla can) you could factor that in as well.

    Too bad Visible Tesla has been abandoned... I believe author was thinking about doing some of this...
     
  6. Andyw2100

    Andyw2100 Supporting Member

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    I could be mistaken, but I expect the app will not do well with a 100% charge scenario. As you know, there is pack-balancing or BMS recalibration or something being done at the end of a 100% charge that causes it to take longer. How much longer this process takes seems, anecdotally, to be at least somewhat related to how long it has been since the car has been charged to 100%. (The longer it has been the longer it takes.)

    I would expect EV CHamp to predict that the car will be finished charging sooner than it actually will be finished, with the understanding that the car may show 100%, but not actually be finished charging.

    Please keep us posted!
     
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  7. Andyw2100

    Andyw2100 Supporting Member

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    I downloaded the app, and then sent the developer the following feature request:

    --
    I just downloaded your app. Unfortunately as it stands now, it would not be useful for me, as I, and I'm sure many others, want to charge at one set amperage level, and never change that.

    I am wondering, though, if you could modify the app so that the variable it was computing was the charge start time.

    So I would provide the starting range, the ending range, the amps, and your app would tell me when I need to start charging.

    You could allow input of any of the variables, and compute the missing one.

    That would make the app a lot more useful to a lot more people.

    Thanks!
    --


    The reason I want to charge at a set amperage level is that in the fall, winter, and early spring, I want to charge just before departure so that the pack is warm from charging, so that my regenerative braking is not limited. And even in the summer, when I charge at a lower amperage, I want to set that once, and never mess with it.

    It would be useful, though, if as I stated in my email message to the developer, the app could compute the correct start time for the charge, with me providing the other variables.

    Since the app can do the computation from the four provided variables, and compute the fifth variable, it should not be difficult for the developer to modify the app to allow input of any four, such that any fifth is computed.

    I'll report back with how the developer answers.
     
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  8. efusco

    efusco Moderator - Model S & X forums

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    good idea. I've used apps that allow you to enter the variable you're interested in and it figures out the rest of the variables. Also, I share your concern about calculating in the taper as more often than not, if it really matters what I want to know is if I'm leaving on a long drive at 8am and I want 100% charge to finish at or just before 8am, what amperage do I need to start at taking into account the taper/top-off time that always seems to take at least 30 minutes to an hour.
     
  9. artsci

    artsci Sponsor

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    Agree --- that would be a very good addition to the app features.
     
  10. EVChAmp

    EVChAmp Member

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    The app currently only does mile-based calculations, but we are looking into updating it to also do calculations based on kilometers. When you say it does not work for cars running metric, are you just saying that it does not display and do calculations in kilometers, or is there some other fundamental problem you are referring to?
     
  11. EVChAmp

    EVChAmp Member

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    The app can figure out what model car you have. We will look into providing an option for choosing to display range as a percentage or distance.
     
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  12. EVChAmp

    EVChAmp Member

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    Such a feature could realistically be added in a future update.

    This is a possibility, but the complication is that the line voltage may vary based on time of day and as the amount of electricity used at your location varies. For example, when your household is using less current, your line voltage can be several volts higher than when your household is using much more current. Also, at nighttime or other times of the day, it may be that your line voltage is lower because your electricity service provider anticipates lower usage at night, and vice versa. The app does not have all of this information ahead of time.

    All these factors are interesting and could theoretically be incorporated into the calculations, but may complicate things more than necessary. We will definitely mull over these ideas over time.
     
  13. EVChAmp

    EVChAmp Member

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    You are correct that the app does not take into account the time needed to balance the pack when it reaches 100%. However, charging usually completes some number of minutes before the end time, maybe up to half an hour, depending on charging conditions, so there is usually at least some time left over for pack balancing to start, if not finish. For the time being, if you want to ensure that pack balancing finishes, you could set the start time in the app one hour later than when you actually are starting, so that you give the battery at least an hour to rebalance itself after it reaches 100%. Remember, this is only for 100% charging, which presumably is a small fraction of your charge events.
     
  14. EVChAmp

    EVChAmp Member

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    We will definitely look into adding this capability in an upcoming update.
     
  15. Andyw2100

    Andyw2100 Supporting Member

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    Excellent!

    Thanks, and thanks too for coming to TMC to be able to interact with us.
     
  16. tga

    tga Supporting Member

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    But given the recent discussions around charging not starting on cold batteries, I'm not sure a delayed, high current charge is better than a slow charge starting right now.

    I think I'd rather charge for 12 hours at ~15A starting when I arrive home with a warm battery after work than for 2 hours at 80A starting at 4AM. Yes, in the [email protected] 80A case, the battery heater should cycle on and off to keep the battery warm before charging starts, but that's wasted power vs power that could be going into the battery (although there's also the inefficiency of lower-rate charging to factor in).

    When I install my HPWC I think I'll install a kWh meter so I can track this stuff.
     
  17. scaesare

    scaesare Well-Known Member

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    Thanks for listening to the feedback.

    Certainly there will be some variability based on voltage and other things you mention. While the app itself could take samples over time to determine the average voltage (which, especially at night is a bit more consistent for me), to make it easier an optional "voltage drop factor" could be a parameter the app accepts.

    In any case, other model EV's have this functionality in their scheduler, and given that they are subject to the same external variable conditions, it should be feasible to get reasonably close I'd think.

    Again, thanks for being open to suggestion. I'd be happy to support folks willing to provide such useful tools...
     
  18. TonyWilliams

    TonyWilliams Active Member

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    #18 TonyWilliams, Jan 24, 2017
    Last edited: Jan 24, 2017
    It's simple math:

    A(min) = (((RR * WhU) / H) ) / V) * (1 / OBCE)

    27.4 amps (minimum) = (((200 added * 285) / 10 hours) / Volts) * (1/0.875)

    You can add to this formula to calculate all the other issues that I list below:

    **************

    H) If you want 200 miles of range at 7 AM, and your low cost period starts 9pm, that's ten hours of charging.

    RR) If you have the brand-new S-100D, and the EPA rated range energy per mile is approximately 335 / (100 *0.95 is the usable capacity) = 285Wh per mile (WhU). EVERY MODEL WILL REQUIRE A SLIGHTLY DIFFERENT FACTOR TO DETERMINE USABLE BATTERY CAPACITY. You only have to calculate Hours (H) once for your vehicle, and WhU works with metric or imperial measurements.

    SOC%) The State Of Charge percent of the battery does not directly correspond to Rated Range (RR) because as the battery degrades, a fully charged battery will still be at 100% but it may have significantly less RR.

    V) The app would have to take into consideration the line voltage supplied; I will just assume that everybody has exactly 240 volts. If your line voltage was 218 volts yesterday, it probably is going to be that well into the future, so you only need to determine this once. I'm referring strictly to Single phase power; three phase power requires a slightly different calculation.

    A) How many Amps, which is the variable that the app is attempting to discover.

    kW) Actual power measure in kW. Power is V multiplied by A which equals Watts. k equals 1000

    kWh) Energy unit of kW power average in one hour

    OBCE) Whatever power (kW) you pull from the wall has a large loss going through the onboard vehicle charger. For the sake of this discussion, we will assume that it is 87.5% efficient. You only have to calculate this once.

    HVAC) The power pulled from the wall may be constant, but net DC power added is variable depending on the battery cell temperature. That's because if the vehicle's battery is significantly cold, the battery heaters will come on and consume a lot of power that would otherwise add EPA rated range to your vehicle. The same is true of cars in extremely hot environments when the air conditioning must cool the battery. This is a huge variable that for the sake of this discussion, I will just assume your battery is at room temperature.

    AGE) Another variable to be considered is internal impedance of the cells. With a high mileage car, the cells will increase with internal resistance, which will decrease the amount of DC energy that is able to be stored and increase heating of the cells, which in turn may require more cooling energy to be used, For the sake of this discussion we will assume the batteries are in like new condition.

    FREQ) Another variable is automatic power reduction. If you are using a UMC and it detects a change in line frequency, that is believed to be dangerous heating of the wall plug, therefore the charge rate will be reduced by 25%. For the sake of this discussion, we will assume that you are using a UMC and wall outlet that are absolutely perfect and that the line frequency never changes from either 50hz or 60hz.

    RRADJ) Finally, you need some kind of adjustment for the actual distance you really want to travel and that won't be necessarily the rated range. For me to drive from my sea level house up to the mountains in the cold winter will take a lot more power per mile. Staying warm and cozy with the cabin heater blasting will take more power still.
     
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  19. scaesare

    scaesare Well-Known Member

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    How does heating affect line frequency? I'd see it affecting incoming line voltage as high resistance points heat up and degrade, but it would seem odd for that to shift line frequency.

    There's been some assertion here that the systems can detect arc-faults, and back current off based on that, but I'm not sure I've ever seen that confirmed. Is that what you are referring to?
     
  20. meloccom

    meloccom Moderator Aus/NZ

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    I entered my Tesla login but it gave an error in red but I can't recall the wording.
    A day later I launched the app and it has my cars name but doesn't seem to be able to down load the current rated range or 90% charge target but perhaps that's not a feature yet or perhaps it can't read it because my car is set to Kms.
    I converted my variables to miles and entered them in and based on my experience it seems to calculate fairly accurately.
    For future enhancements most other countries also have 3 phase power available so that would be a nice option to have in the variables.
     

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