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Charging 2 Teslas in a sequence

Discussion in 'North America' started by wolfpet, Jun 11, 2018.

  1. wolfpet

    wolfpet Member

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    Apologies if this has been answered already; the forum search hasn't returned much.

    I currently have 1 HPWC at 40 amp. This is all I can do without a costly upgrade to my house and this is more than enough for the amount of commute we do, but sharing the plug is not very convenient. Now, I would like to add a secondary HPWC to be able to plug both cars at the same time. I would like it to be automatically powered off while the first car is charging and turn on when the first car is done charging. It should work similarly to the Dryer Buddy, where the dryer and a car charger can share a single 240v outlet and work in a sequence. I wonder if some sort of standard solution exists that allows two devices to work in a sequence. Has anyone done this for your 2 EVs? Thanks!
     
  2. ai4px

    ai4px Member

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    The newest generation of HPWC (since 2016) has communication ports to allow you to share power. You set the charge rate of the first one and set the others to "slave" mode. They must be connected by a two wire cable to allow them to communicate and work out the power draw details.

    I looked into using two Juice Box EVSEs for sharing, but they don't communicate directly with each other. They use the JuiceNet server. If your internet is down, they default to 8 amps per car. I found this unacceptable since I'm rural and my internet goes out more than my power.

    Another solution is the Siemens versicharge. It has dry contact inputs for inhibiting charging. So you can cross connect two Versicharge units such that when one is charging the other won't charge at all. It would be possible to tap in to the HPWC's 220v contactor and use that to inhibit the Versicharge, but that's not for the faint of heart.

    I think the solution you are looking for is just to get two HPWC's and connect their communication lines together.
     
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  3. hiroshiy

    hiroshiy Vendor

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    The latest Wall Connector does have a load sharing feature.
    Model S/X/3 Wall Connector
    It's not like charging in turn, but prioritize lower SOC (state of charge) car and allocate more amps.
     
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  4. wolfpet

    wolfpet Member

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    Thanks this is very good to know! I didn't know that the new HPWCs support master-slave cascading. This helps a lot! I just got my old HPWC replaced and my second one is a "present" from the referral program, which I think should be a new model as well. So that's the route I'm going to take.

    I'm curious though if a standard electrical solution exists that doesn't rely on the chargers negotiating. Say, if the first consumer is a dumb dryer and the second is a charger, etc.
     
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  5. DOCAL

    DOCAL Member

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    As people have said, the HPWC can load share, so both cars charge in parallel but the total load stays within bounds. When car1 finishes car2 will automatically ramp up to full.

    If you must have it staggered, the API that the phone app uses would let you do it. If you know some programming, you could poll the cars and send the start-charging command to the 2nd one once the 1st is finished.
     
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  6. David99

    David99 Active Member

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    As mentioned, you can do it fully automatic by using two new HPWCs.

    The cheapest method would be to just use the UMC on the second car and set the timers on the cars in a way they don't charge at the same time. Or set both cars to half the power and then don't worry about time.
     
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  7. ai4px

    ai4px Member

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    Oh and one more thing... There's a Smart EVSE as a semi-kit that has the option for a current tap for sharing. You could hook it up to measure the current draw from the HPWC or a clothes dryer
     
  8. Daniellane

    Daniellane Active Member

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    The way I accomplish this is by leaving one car unplugged until the other car has completed charging.
    Another option would be to simply start one car charging and then set the other car to delay charging until approximately the estimated time that the first car is expected to be completed. Although I have not tested this and I am not sure that it would not split of the amperage to some degree while both are plugged in.
    I posted this demo on YouTube:
     
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  9. Rocky_H

    Rocky_H Active Member

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    A few options, mainly mentioning for someone else's future reading who has a similar question:
    1) The Tesla wall connectors sharing is perfect, and you already have one.
    2) Clipper Creek does make wall connectors with this sharing feature also, called Share2. But they're a little pricey, at $1,498 for a pair of them.
    32A Level 2 EVSE Share2® HCS-40 Bundle| ClipperCreek
    3) Yes, I do have a friend here in town who has two 14-50 outlets on the same circuit (which is not allowed now as of NEC 2017 code). They have one car set to charge any time it's plugged in, and the other set to charge at some really late time, like 2 or 3AM. The first car is done before the timer on the second one starts, but that's far from foolproof if the first car runs long, and there has been a time or two it has tripped the breaker. I wouldn't really recommend this.
    4) Split your circuit into a 30A and a 20A if you want. Both can run at the proper levels of their circuits, and won't interfere with each other, and that's still generally enough for overnight charging.
     
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  10. ai4px

    ai4px Member

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    There is a product called a Dryer Buddy that has a current sense relay. If you turn on the dryer while the car is charging, it'll kill the power to the EVSE. The shutdown will be abrupt and your car may send you a message saying charge was interrupted.
     
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  11. ai4px

    ai4px Member

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    I too have considered setting the HPWC to 24 amps and the siemens versicharge to 16... total of 40amps if both cars end up charging at the same time.
     
  12. ai4px

    ai4px Member

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    Thank you so much for posting this. I had heard that the car with the lower SoC would continue to charge the fastest, but it seems no matter the SoC, the HPWCs simply split the available 80amps. I had wondered how the car communicated with the HPWC to indicate SoC and I see it doesn't.
     
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  13. Rocky_H

    Rocky_H Active Member

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    Let's be clear on the types of Dryer Buddy, because the regular Dryer Buddy you refer to does NOT do that.
    "Dryer Buddy" just ties to two outlets onto the circuit--no protection or lockout of any kind.
    "Dryer Buddy Plus" has a toggle switch, so you manually select one or the other.
    "Dryer Buddy Plus Auto" has the current sensing, so it will auto switch.
    Early on, when those first came out, people tested it, and they did actually do that function, allocating by state of charge. I don't know when they changed it or why, but apparently it's different now and doesn't do that.
     
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  14. miimura

    miimura Active Member

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    When you use Tesla Wall Connectors and you want the cars to charge sequentially, not simultaneously, you can still use the power sharing feature and use in-vehicle charge timers to stagger the charging.

    Of course, you should know that any plugged in car will be reserved 6 amps, the minimum pilot signal. So, if you are sharing a 60 amp circuit that can deliver 48 amps to one car, you would be limited to a maximum of 42 amps for the first car to charge since 6 of the 48 are reserved for the other plugged-in car. If you really want all 48 amps, you have to unplug the other car. If you only have 60 amps of capacity left in your main panel, then sharing the 60 amps is far preferable to installing two 30 amp circuits.

    I have not observed this 6 amp reserve behavior with my own eyes, but I recall reading this on this forum.
     
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  15. Daniellane

    Daniellane Active Member

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    These screenshots were taken seconds apart . It appears that at times one car can get max amps while both cars are plugged in. In my case the 100 amp circuit maxed out at 80 amps which allows up to 8 additional amps for our Model 3 when it is not charging. So staggering charging times with 2 wall chargers on one circuit for sequential charging could be easily accomplished.
    8FAD473D-7D76-4A5A-8553-F30C4642E7C8.png 71FBD901-7054-4498-AD88-D82F150E3D27.png
     
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  16. FlatSix911

    FlatSix911 918 Hybrid

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  17. ai4px

    ai4px Member

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    Ok I understand sharing now. The units will equally divide current between all Hpwc units. So if you have 50 amp max and two units each car will get 25 amps. As one car tapers off it’s charge and draws less that 25 amps, the hwpcs will recognize that and allocate the left over amps to the other units.

    From the manual: During steady-state operation, the load sharing network toggles available current to each vehicle in 2A increments, every minute, to asses vehicle need. When a battery approaches full charge, the power consumption will taper until charging is complete. If the master unit detects that a vehicle is no longer using all of its available current, it will reduce the current allocated to that vehicle.
     
  18. tga

    tga Supporting Member

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    Do you have a reference for that? I was debating with a friend whether this was allowed or not. I couldn't find anything (but my city still uses 2014).
     
  19. nwdiver

    nwdiver Active Member

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    What kind of upgrade did you look into? Upgrading the Distribution Panel would indeed be VERY costly because it's labor intensive. ~$3k would not be unreasonable. An alternative would be tapping off your meter base. It should be possible to connect a standalone 60-100A breaker directly to your meter base then use that to feed your HPWC. This would also make charging slightly faster and more efficient. Not sure about electricians in your area but my company would be able to do this for <$500. This is what we have to do if we want to install >8kW on a 200A service...

    [​IMG]
     
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  20. Rocky_H

    Rocky_H Active Member

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    I've searched a little, but I can't quite find the reference. However, @eprosenx has been reading the new electric vehicle code sections a lot and can probably find that. Do you know the line that says an outlet installed for electric vehicle charging has to be the one dedicated outlet on a branch circuit? I think that was recently added to the NEC section 625.
     

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