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Adding car charger to Powerwall?

Discussion in 'Tesla Energy' started by cwied, Jun 7, 2018.

  1. cwied

    cwied Member

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    Here's a question to the electrical experts in this forum. I'm in the process of buying a Model X, and would therefore like to add either an HPWC or a NEMA 14-50. When Tesla installed my Powerwalls, they added a "Do not add loads" sticker to the load panel. Is this an absolute, or is there a possibility the panel may have enough capacity to add the charger?

    In practice, the highest consumption I've ever seen in my house is about 11 kW. I have 200 amp service and the load panel also seems to be rated at 200 amps.

    The significant loads I have are 2 AC units (one 4 ton, one 2 ton), electric dryer, 2 refrigerators, electric oven and a microwave. The range, hot water and heat are gas.
     
  2. wwhitney

    wwhitney Member

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    To answer your question it would be best to have a complete one line diagram of your electrical installation, showing each panel, each feeder, the supply equipment, and the loads in the each panel.

    However, you can start with the details of the panel with the "Do not add loads" sticker on it. What size is it, how is it fed, are any sources (PV/Powerwall) connected to it, and what branch circuits (loads) originate in it?

    Cheers, Wayne
     
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  3. mongo

    mongo Well-Known Member

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    Tesla has limits to the amount of load in a panel backed up by powerwalls to stay within their maximum output. I think the guideline is no breaker larger than 30A * number of powerwalls (7kW max output each) along with 5kW continuous load per PW.
    A 50A EV charge plug would likely exceed design capacity, but each situation is unique. How many PW do you have?
     
  4. cwied

    cwied Member

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    I have two Powerwalls, so a 50A charger would be the limit, as I understand it (60A breaker for the 50A circuit).

    The one-line diagram is probably beyond my ability to generate, but here are some pictures:

    Overview of the panels. From left to right: Generation panel (powerwalls+solar), Load Panel, Tesla Gateway, Main Panel.
    [​IMG]

    Main Panel (only the 200A breaker is connected):
    [​IMG]

    Load Panel (200 amp rating):
    [​IMG]

    Generation Panel:
    [​IMG]

    Sub-panel A (inside house):
    [​IMG]

    Sub-panel B (inside house):
    [​IMG]
     
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  5. mongo

    mongo Well-Known Member

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    I don't see a physical issue with adding a 50A or 60A breaker for EV charging to the main panel since it would be the only load and both feed directions to the panel are protected by 200A breakers. Excess solar will still go to EVSE (although it would prioritize PW charging first).


    However, the total load may be too high. Need the nameplate ratings of the AC and appliances along with house sq footage for the load calc.
     
  6. Jeffgtx

    Jeffgtx Member

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    just call tesla and ask them. hey have the calculations and i went over everything i wanted to do and my options for changing and they answered them right away.
     
  7. Big Earl

    Big Earl Supporting Member

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    If you run all of your major electrical appliances simultaneously, what is your max load?

    I'd expect 4 kW for the large air conditioner, 2 kW for the small air conditioner, 6 kW for the electric dryer and 8 kW for the electric oven. The refrigerators will be about 500 watts each (more if they're running defrost cycles), 1 kW for the microwave and 1 kW for the dish washer. Rounding up, this is about 100 amps.
     
  8. SoundDaTrumpet

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    #8 SoundDaTrumpet, Jun 7, 2018
    Last edited: Jun 7, 2018
    Thanks for posting the photos. I believe that with the EV chargers, the 200A main breaker will likely need to be downsized. The "do not add loads" sticker is driven by an NEC load calculation that when combined with generation (solar + battery) will never exceed the busbar capacity of the stated 200A (225A typically from Tesla) busbar. Appliances used in my NEC load calculation by Tesla exactly matches yours except I already have 50A allocated for EV charger. My design can handle another EV charger.

    Other takeaway for others: (a) I noticed that the old circuit breakers were left unused and in place. This sure beats using filler blanks which I perceive as being unsafe. Also noted that a new dead front replacement was not done. (b) Since I have a main lug only panel, with a optional main breaker that is no-longer manufactured, it is clear that this is the reason why my service meter-load center combo is being replaced.

    Nit: You are missing a "battery disconnect sticker" on the left side. In the event of being in a hurry (firemen), one will easily skip over turning off one of the batteries.
     
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  9. cwied

    cwied Member

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    @mongo, @SoundDaTrumpet: thanks for the analysis.

    For the load calculation - the house is 3400 sq. ft. For the appliances, AC1 has a 21.8 amp RLA and 1.3 amp FLA, AC2 has 12.8 amp RLA and 1.2 FLA, the dryer is rated at 26 amps, Microwave Oven 1.5 kW. I can't find the ratings for the refrigerators or the oven, but I know the oven pulls about 6 kW when preheating.

    @Jeffgtx: who did you talk to at Tesla? I've had such a bad experience talking to Powerwall support that I was reluctant to call them. They told you how to add a charger to Powerwalls after the fact?
     
  10. SoundDaTrumpet

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    There are two parallel thoughts:
    1. EV charging on the MAIN panel.
    2. EV charging on the LOADS panel.

    The NEC load calculation applicable to (1), I estimate @cwied at 125A.
    (a) This says you have ~75A available for EV charging.
    (b) This says what the main breaker can be sized down to to support (2).

    For NEC load calculation applicable to (2), I would need help from others such as @wwhitney to elaborate.
     
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  11. wwhitney

    wwhitney Member

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    For whatever reason, I am unable to see the photos.

    I'd still be interested to get the details about the panel that says "Do not add loads." Which one is it?

    Your wiring system sounds like it starts as Meter -- Main Panel with just one 200A load breaker -- Backup Gateway. That's a very common Tesla arrangement.

    From there it likely goes Backup Gateway -- Loads Panel -- Subpanels A and B. The question is where does the Generation Panel connect, into the Loads Panel or directly into the Backup Gateway?

    Cheers, Wayne
     
  12. boaterva

    boaterva Supporting Member

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    I can't see them at all either. How are you posting them? It should be just upload using the 'upload an image file'.

    Is there some issue with attachments recently? I've seen this several times recently, and not sure what's going on...
     
  13. cwied

    cwied Member

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    Here's a link to the pictures: https://photos.app.goo.gl/75aoNMQRMfom5bDE3. I think TMC's picture handling is broken somehow. I'm actually using cut-and-paste to post, which has worked without problem in the past.

    As far as I can tell, the Generation Panel is wired into the Gateway directly. At least I don't see a breaker corresponding to generation in the Loads Panel.
     
  14. boaterva

    boaterva Supporting Member

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    Hm, I paste small screen captures with no issues.... so, that's weird. Thanks for the link!
     
  15. wwhitney

    wwhitney Member

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    An overview picture like the first one you posted, but with a broader view so that we can see where the conduits go above and below, would be helpful.

    If there are no generation sources connected through the Loads panel, then I'm aware of no reason not to add further loads to the Loads panel. Do you have a "Do not add loads" sticker on your exterior main panel? If not, then that sticker on your Loads panel was misplaced, it should be on the main panel. If so, I think they just got carried away with the stickers.

    An NEC load calculation would be the proper thing to do first, but those load calculations are very conservative. So even if the calculation came out to 250A, you'd probably wouldn't have any difficulties in practice.

    BTW, a 60A breaker is only adequate for a 48A (continuous) EVSE, not a 50A EVSE.

    Cheers, Wayne
     
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  16. cwied

    cwied Member

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    Unfortunately a broader view is not that helpful because all the upper conduits go into a gutter box just out of frame. The conduit that heads left from the generation panel goes to the Powerwalls. The conduit heading down from the generation panel goes through the wall and out to the solar inverter. The conduits heading down from the load panel head to the smaller AC and I believe the garage plugs. I suppose I could see if I can easily open up the gutter box to trace the wires, but given that there are no breakers for the generation sources, I assume that they're just going straight to the Gateway.

    There are a bunch of stickers outside, but no "Do not add loads." I did notice that they also left a dual-power warning sticker on the door to the cubby that holds the panel, which I probably should replace with a tri-power sticker.
     
  17. SoundDaTrumpet

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    I am puzzled why you have a "Do not add loads" sticker on the Eaton LOADS panel because (a) LOAD panel appears ready to accept more loads, and (b) The meter panel seems to be a better place to put the sticker. NEC load calculation is 125A for you there and have 100A of PV & PW 'load' at the gateway. If the service panel bus load is 125A plus 100A it might make sense for the label to go to there.

    More findings/nits:
    1. The bus stab max is 200A on the Eaton panel. You have a 125A breaker and 100A breaker directly across. I just read about it and seems to violate UL of Eaton panel. Correct me if I am wrong.
    2. The 125A breaker and 100A breakers look incorrectly labeled as well.
     
  18. wwhitney

    wwhitney Member

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    OK, I'm pretty convinced that the sticker on your Loads panel is misplaced and you should move it to your main panel.

    Of course, you shouldn't trust advice you get on the Internet. In your situation, I would trace the feeders through the gutter and establish for myself that only one source is feeding the Loads panel, not multiple sources. In which case there is no reason not to add other loads to that panel.

    The "do not add loads" sticker is one method of protecting the busbar on a panel which is fed by multiple sources, namely (2017 NEC) 705.12(B)(2)(3)(c), which requires that the sum of the breakers excluding the main breaker not exceed the rating of the busbar. (CA is on the 2014 NEC, where the section is I believe 705.12(D)(2)(3)(c), the article got reordered in 2017.)

    Cheers,
    Wayne
     
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  19. mongo

    mongo Well-Known Member

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    Hey Wayne, does this make sense?

    The load panel is the backed up panel. If it has more load than the power walls can provide (night with no solar), the system will trip out. Thus the warning not to add additional loads.

    The main panel is fed by 200 Main breaker and 200 A gateway breaker. The gateway breaker is not properly positioned for back feeding of other main panel breakers (would need to be at bottom, so my earlier post about adding a breaker is incorrect). In terms of bus bar capability, a breaker or two in the middle (really up to 200A load) with relocated gateway breaker would be less than 200A at any point in the panel.
     
  20. wwhitney

    wwhitney Member

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    The only way in which Tesla enforces this idea is their rule about no breakers larger than 30*N when you have N Powerwalls. During a power failure it's always up to the homeowner to manage their aggregate load to not draw too much at once and trip out the Powerwalls. With the existing loads in that panel, that's already any issue.

    Of course, a really big load like an EVSE would make it alot easier to overload the Powerwalls during a blackout. Or if your car is charging at night and there is a blackout, your Powerwalls could easily be depleted while you are asleep. For that reason I put my EVSE in my (normally) non-backed up panel.

    What you say is correct physics-wise, in fact there would be no reason to relocate the gateway breaker. All that would be required to protect the 200A bus is that the sum of any additional breakers be less than 200A. That covers the case that the gateway breaker is a net source; if the gateway breaker is a net load, then the bus is protected by the 200A main breaker as usual.

    However, there's no rule in the NEC that recognizes this, the available rules are more limited. I may submit a "public input" in 2020 for a possible revision to the 2023 NEC; unfortunately it is too late for the 2020 NEC.

    Cheers, Wayne
     
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