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Idea for Tesla: Intelligent Charge Setup

Discussion in 'Charging Standards and Infrastructure' started by smorgasbord, Jun 14, 2011.

  1. smorgasbord

    smorgasbord Active Member

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    I've learned a lot reading these forums. For instance, I've learned that keeping the battery at a 50% charge is better for the battery than keeping it at the "Standard" full charge (~90%). I've learned that it might be better to charge at lower amperage than higher, and even if not, doing so is easier on the grid. I've also learned that ideally the car should reach a full charge about 30 minutes before its next driven, so that balancing can be performed.

    With that in mind, here's my proposal for what I'm calling ICS: Intelligent Charge Setup, which optimizes battery life and, for those on Time Of Use (TOU) metering, also optimizes charging cost while ensuring that you have a full charge the next day, or at least as much charge as is possible.

    Today the driver optionally enters a Start After time and maximum amperage. For ICS, the driver enters:

    1) The earliest time you will want to drive the next day. I call this the "Ready By" time.

    2) (Optional) The start/end times for Off-Peak, Part-Peak, and On-Peak at your location. That includes seasonality and weekday/weekend differences. (note I have a simpler entry possibility later)

    3) (Optional) The maximum amps to draw. Just like today.

    That's it. You connect up and your car is ready to drive the next day utilizing the lowest available cost power and at the slowest rate possible so the battery isn't full for too long but yet is fully charged in time to balance itself before you drive off.

    So, what's the logic behind this? Pretty simple, really:

    The car knows the battery's State of Charge (SOC), and so given the maximum amps it can draw, it can calculate how long it will take to reach a full charge and therefore time that period to a) occur during the cheapest available power rates and b) use the lowest amps to both fit within the cheapest power rate times and be full in time to do a 30 minute balancing before you leave the next day.

    From the current time, the car knows if there's an Off-Peak time between now and when you want to drive and it can determine the right amperage to use starting when the Off-Peak starts and ending either 30 minutes before you want to drive or when the Off-Peak period ends (whichever comes first).

    If the available Off-Peak period and maximum available amps aren't enough to fully charge the battery (or if there is no upcoming Off-Peak), it can try to take advantage of any Part-Peak times, and if that fails, well, it uses as little Peak kWh as it can to still reach full charge in time for you to leave.

    Now, if you don't have TOU metering, or you don't want to bother entering that information (although it's a one-time thing for your home location), you can just enter a Start After time (like today it's optional) as well as a Ready By time. The car will then start charging at the Start time (like today), but limit amps so that it is fully charged a 1/2 hour before the Ready By time. If it wouldn't be ready in time at that rate, it'll start charging sooner - the idea being that it's best to start the next day with a full charge no matter what.


    Tesla, please consider this as both a firmware upgrade to the Roadster as well as to incorporate into the Model S from the get-go. "Ready By" times are more important than "Start After" times, and easier to understand, and since many customers are on TOU metering, it would enable the cheapest charge ups without the drivers doing any math.
     
  2. markwj

    markwj Moderator, Asia Pacific

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    There is a separate thread here talking about inefficiencies of slow charging in hot climates. I suggest that the trade-off of charge current battery life vs hvac usage should also be taken into account.
     
  3. kgb

    kgb Member

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    This was discussed partly in another thread.
     
  4. scott451

    scott451 KWH-PWR#1349Sprt,S Sig#96

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    #4 scott451, Jun 14, 2011
    Last edited: Jun 14, 2011
    The real enemy is heat not SOC

    Checkout partial-discharges: Proper Care Extends Li-Ion Battery Life Pg 2 of 3
    And this Battery information from Battery University


    Below 85%, SOC is not the enemy, it is temperature and depth of discharge (DOD). Keeping the battery at 50% for "non-storage" (i.e daily drive) is a bad idea. Here's why, say you use 25% SOC to drive your route. In your case, you'll start at 50% and end at 25%. A fully charged Tesla in Standard will start at 85% and end at 60%. The deeper discharge will shorten battery life. Running your car at lower SOC, causes the battery to run hotter (for the same power draw), because the internal resistance of the battery increases as the SOC decreases. The max current draw out of the battery pack is about 5C. you really don't want to draw 5C out of a pack when your SOC is 25%.

    The real enemy is heat. The Tesla tattler has a cool down algorithm that tries to minimize the battery temperature regardless of the SOC or time of day. It understands TOU and will cool the battery to 70F if you are outside the TOU cheap charge time. Otherwise it will let the car charge. It would be pretty ease to add a "Be ready by time" like the Nissan leaf has (and you described). An example: you go out for a spirited drive and your SOC drops to 55% and the battery temp reaches 90F. You come home and plug into the charger. The tattler sees that the battery is hot, but that it's the wrong TOU to charge. The tattler will cool the battery for about 20minutes until it reaches 70F and then wait for the scheduled charge.

    Charging at 40A is a charge rate of about C/4. That's pretty slow. Charging at 20A (C/8) wouldn't add much to the battery life.

    Can you provide a reference? I believe that (and have seen) there is a balancing phase at the end of the charge. Right after the charge completes I haven't seen balancing occurring (as seen in the VDS screen). However, the battery sheets continually monitor the balance of their bricks and broadcast it over the CAN bus to the rest of the sheets. It's not clear from the patents if they dump the mismatch in to a power resistor, or redistribute the mismatch to the lower cells. both are claimed in the Tesla patent.
     
  5. smorgasbord

    smorgasbord Active Member

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    First, thanks for the great reply!

    That's not what I was saying at all - sorry if I wasn't clear. My thinking was to keep the battery around 50%, but then start a charge to full such that it completes in time for the next day's drive during the off-peak time period.


    Can the Leaf also be programmed to know when the Off Peak time periods start and end? if not, then if you tell the car you're going to leave the next day at 6pm, you might end up charging from noon to 5:30pm, which is probably more expensive (and grid challenging) On Peak.


    OK, but it might be easier on the grid. I guess we'll know EVs have "made it" when people start complaining that the power grid gets taxed at 9:01 pm when all the cars kick on to recharge during the time period previously known as "Off Peak."


    No, it was from a post in this forum that I read. It's probably somewhere in the gi-normous 58 page charging thread. Whether the balancing occurs during the end of the charge or just after the charge isn't important to my suggestions as long as whatever time is needed is encapsulated in the start time and amperage calculations.
     
  6. TEG

    TEG TMC Moderator

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    The Leaf itself doesn't have that option, but those with Blink brand J1772 EVSEs can program TOU rates into their charging station and have it control when the car is allowed to charge.
    There is a small 'battle' going on in terms of what should be in charge of the charging times... The vehicle or the EVSE? For now, I just leave my EVSE unconfigured, and use the time of day charge settings in the Leaf, but they are just based on one set of time ranges not directly associated with any TOU. If I ever want to charge the Leaf outside of the night time range I configured, I have to push the manual override (force charging to start) button in the car.
     
  7. TEG

    TEG TMC Moderator

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    By the way, since the Leaf has no active thermal management of the pack, I have heard suggestion that it is a good idea to let the pack sit for a while (to equalize to ambient temp.) before charging.
    Another reason why having a delayed start is good. Not just to get into lower TOU rates, but also to let the pack cool down first.


    This is unlike the Roadster, or even my old RangerEV where active cooling can start as soon as you go on charge.
     
  8. smorgasbord

    smorgasbord Active Member

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    I just had an email exchange with my Customer Advocate, and he confirmed that balancing starts after it has completed charging when in Standard mode, that balancing takes about 30 minutes, and that balancing is important to getting the full potential out of the battery pack. An imbalanced pack will not fill up all the way in any mode, nor will it be able to discharge as far.

    He also said that Standard charges to car to about 87%, whereas Range and Performance charge to about 97%. Also, if a pack is out of balance, it may take several charge/balance cycles to bring it back into balance.
     

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