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New Power Wall Connectors - "sharing" observation

Discussion in 'Model S: Battery & Charging' started by 2virgule5, Sep 28, 2016.

  1. 2virgule5

    2virgule5 Member

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    We just took delivery of our X75 in addition to my S90D - family's transition to zero emission vehicle is now complete.

    To charge both I've installed 2 PWC on the same line on a 60A breaker with the sharing function. My expectation was that when both cars are charging current will be split, so 24A each. To my surprise it doesn't really work that way: the system is dynamically balancing current so both cars will finish charging at the same time. For example my S SOC was significantly lower than the X, so it received in that case 28A while letting the X having the remaining 20A, and through the App I could see both would take the same time to reach their programmed 90%.

    To test this I set the SOC target of the S to 100% and it started soon after to increase current to 30A for the S and 18 for the X. I think it is a neat feature (that I was not expecting, did not see that in the manual or description).
    Now out of curiosity I'd like to know who's doing the control, ie car to car communication through the PWC or directly the master PWC?
    And for you out there with more than a PWC did you notice the same behavior?
     
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  2. kirkbauer

    kirkbauer Member

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    That's interesting. Are the two PWCs connected by anything besides the 60A power line?
     
  3. habanero69

    habanero69 I Dont Need Cialis. I Drive an EV.

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    There would be no car to car involvement. I would assume that the 2 PWC are doing a balancing act based on algorithm and knowing what each load is and the charging characteristics for each car to reach max charge at max rate. Maybe there is some documentation on how this is done within the PWC, but probably something Tesla won't be sharing at the detailed levels...
     
  4. 2virgule5

    2virgule5 Member

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    @kirkbauer Yes as part of the installation manual there is a communication cable between the two (you can daisy chain up to 4, 1 master that is the one to receive the line).

    @habanero69 that is also my thinking, but it would require the car to somehow state what the SOC is to the HPWC, by default it is going to ask for the max juice the HPCW decides to provide.
     
  5. davewill

    davewill Member

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    This was mentioned before as a feature. Likely the HPWC gets the info from the car via CAN like the Supercharger does.

    At first glance, not a terribly useful feature, since the two cars would still have finished even if the split was even. However, it might have the effect of maximizing the circuit by not having one car drawing only half the circuit capacity when the other one is throttled way down because it's almost done. Probably not a big difference, though.
     
  6. rfmurphy81

    rfmurphy81 Member

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    Slightly off topic (sorry), but I wish there were a way to track how much power each wall charger was sending out in any level of detail. When I have my S and the upcoming 3 in my garage, I'd like to be able to accurately track how much each car is using. This is especially important as I didn't get a separate sub panel set up so it's all getting merged with all usage from my property.
     
  7. gavine

    gavine Petrol Head turned EV Enthusiast

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    Could be designed that way for destination chargers where multiple cars might be charging at the same time and they want to give more AMPs to the car(s) with the lower states of charge. Or, is it first come, first serve like the Superchargers?
     
  8. araxara

    araxara S-P85#3,218 X-90D#3,299

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    I have 2 HPWC's connected to 2 separate 100A breakers (set for 80A operation). The HPWCs are wired for master/slave operation (shared). I also have a Model S P85 with 80A charger and a Model X 90D with 72A charger. When both cars are plugged in and one car is full and the other car is charging, I never get the full current for the car that needs to charge - even when the non-charging car is "sleeping". Once I unplug the car that's not charging, the car that is charging gets the full current. It's seldom that both cars need to charge at full rate at the same time, but for those times I have observed that they both charge at 40A. When they need to charge at different rates (like when one is topping up to 100%), the current seems to be divided unevenly - but I haven't bothered to figure out if they would finish charging at the same time.

    As an aside, these are the second set of the new HPWCs I have installed. The first set died together at the same time, taking out the main charger in the Model S. The service center thought it may have been a power surge. The original set had constant problems with load sharing and would generate error codes.
     

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