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208v charging condo

Discussion in 'Model 3: Battery & Charging' started by coconutboy84, Dec 1, 2019.

  1. coconutboy84

    coconutboy84 Member

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    Hey guys. I had my hpwc installed a while back and it’s in my condo underground. It’s 208v 60amp which means my M3 SR+ will charge at 6.6kw instead of the 7.6kw it’s 32amp charger isn’t rated for. Two random stupid questions then....

    1) is the 32amp charger in the Sr+ a hardware or software limitation? It would be awesome to upgrade to 48amp eventually if possible.

    2) I know the Nissan Leaf can adjust to lower volts by upping the amps to compensate. You think Tesla might do something like this in the future?

    I know these are probably dumb questions but charging at a slower speed on an already slower 32amp hpwc is just kinda crappy lol.
     
  2. Sophias_dad

    Sophias_dad Supporting Member

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    I understand the 32 amp charger is a hardware limitation. They depopulated the charging board of a 48 amp charger to save money. The chargers have different part numbers. Someone else already asked about the upgrade and I gave no guarantees about it being possible...ever. You'd have to dig into the top of the battery assembly, accessed under the rear seat. Its not a DIY thing by any means.

    If you really wanted, you could appreciably improve the charge speed by using a pair of boost transformers to get the voltage up to 277 or thereabouts... the 3 is apparently tolerant up to around 300! I've used 277 on my 3, occasionally hitting 283...

    Here's one that will take you to 260 from 208...1 KVA Transformer Primary 120 x 240 Secondary 12/24 Federal Pacific K1XGF12-1... you'd need two, one for each of the two legs that's contributing to your 208.

    1.5 KVA Transformer Primary 120 x 240 Secondary 16/32 Federal Pacific K1XGF16-1.5 would take you to 283V at the output of the transformers, but with some losses along the way, it would probably be fine. Notably, with a slightly different wiring, you can also get 264V out of them(assuming your 3 decides 283 is unacceptable!)
     
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  3. gfunkdave

    gfunkdave Member

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    There is no free lunch. If you use a transformer to bring yourself up to 277 V and you are expecting the 48A max input into the car at that voltage, that means you'll be pulling 13.3kW. In order to pull 13.3kW on your 208V primary, that means you'd need a circuit able to deliver 64A.

    The Tesla will certainly raise the amperage to the max that it identifies the circuit can handle, either based on the HPWC's signaling or the signaling of the adapter plug you use to plug into an outlet. You aren't experiencing some odd "low voltage" situation. 208V is the standard voltage for three phase power. You will by definition just charge a little more slowly than you would at 240V. But even at the 32A max from the UMC, this should be plenty to recharge overnight.

    I wouldn't worry about it.
     
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  4. Sophias_dad

    Sophias_dad Supporting Member

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    Yes, OP is limited by the 32 amp charger in the car, and yes, you'd need to feed the boost transformers with more than 32 amps in order to get the 32 amps output. Hopefully anyone installing them would know that.

    I agree that most folks should be just fine adding ~27mi/hr on a 200V/32A charge rate.
     
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  5. coconutboy84

    coconutboy84 Member

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    thanks for the info guys! ill def look into it with my electrician. I know overnight charging is no biggie at all, but the reason i ask is that im a real estate agent and i tend to go out and do some driving for work, then come home, charge for a bit, then go back out sometimes. sometimes multiple times throughout the day, so a quicker charge would def be helpful.
     
  6. gfunkdave

    gfunkdave Member

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    This is what Superchargers are for. :) Is there one by you?
     
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  7. Kevy Baby

    Kevy Baby Dis-Member

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    Not speaking for anyone else, but charging at home (where you can do many productive things) is MUCH more efficient than stopping at a SC, even if the charging is slower.

    YMMV
     
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  8. coconutboy84

    coconutboy84 Member

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    oh for sure, i am in ontario so there are a few, but they arent really on my way home. i know the 30amp charge is really no big deal, was just curious if there was any other solutions.
     
  9. ewoodrick

    ewoodrick Well-Known Member

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    Do you need more charging? Or are you charged in a few hours like most folks.
     
  10. Tessaract

    Tessaract Member

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    I haven't looked at the transformer spec sheets, but if they are 1.5 kVA transformers, then they are themselves limited to handling much less power than the Telsa SR+ on board charger is limited to. Not a useful solution.
     
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  11. Sophias_dad

    Sophias_dad Supporting Member

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    They don't need to handle the full power... just a fraction.... I haven't done the math to figure out where the 1.5kva comes from, but I got the recommendations straight from the manufacturers calculation tool.

    I imagine the rating is essentially the difference in amps between the input and the output windings times the input voltage. Its only the 'boost' that needs transforming... For instance, the first option I gave has a max input current of 41.7 amps, and a max output current of 33.3 amps... that's 8.4 amps of difference... the input voltage for each of the two transformers(legs) is 120V, and 8.4*120=1.008 kva..... an almost perfect match for the 1 kva rating of the transformer.
     
  12. Tz00

    Tz00 3 LR AWD

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  13. Sophias_dad

    Sophias_dad Supporting Member

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    1.5 KVA Transformer Primary 120 x 240 Secondary 16/32 Federal Pacific K1XGF16-1.5 , aka K1XGF16-1.5
    is the rough equivalent of the Larson unit you suggested. I got it from Buck-Boost Transformer Calculator/Selector - Federal Pacific using single phase, 208->240, 32 amps.

    I did not suggest a single phase transformer because I'm not sure how the HPWC would react to having its two supply legs running at different voltages from ground.


    Buck and Boost Transformer Calculator - Schneider Electric United States is another handy calculator.... It suggests "1.5S46F" as the best transformer for this job, and lists its "actual kva" as 11.04. But that 1.5 is still prominently displayed in the model number. If you go to www.squared.com and look for its datasheet and installation instructions, the datasheet clearly says "Rated power in VA 1.5 KVA", and the installation instructions describe how to install it to get to 236 volts from 208, and further list that as "Load KVA: 11.0"

    It appears to be a question of nomenclature.
     
  14. eprosenx

    eprosenx Active Member

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    There is quite a bit of incorrect information in this thread. I don’t have time right now to respond to each post, but here is the high level:

    You would not need two transformers to step up 208v to something closer to 277v. One autotransformer would do the trick.

    It is true that you would get more charging speed if you take the 208v at 32a up to something higher voltage wise. We do know that the 48a M3 chargers actually do have some kind of limit whereby at 277v they will back down the charge amps slightly since there is some overall limit. My guess is the 32a charger is likely the same, but I don’t know that anyone has tested it and posted results.

    Of course, as pointed out, if you boost the voltage up then the amps drawn on the transformer input will be higher than the amps powering the car. Circuits and breakers will need to be sized appropriately (but it sounds like you already have a 60a breaker that your car can’t use fully due to its limits).

    I need to point out that autotransformers (which is what a buck/boost transformer generally is) are very interesting devices. Their rating only applies to the amount that is being raised/lowered in voltage. So if you are only raising the voltage say 25% then you only need a transformer rated for that 25% of the overall load. (refer to the manufacturer specifications- I am not an expert in this actual calculation, but that is the gist of it).

    I would in general question whether trying to get that extra marginal charge speed would be worth it. Generally this is not an issue for overnight charging, but the real estate agent use case makes some amount of sense!
     
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  15. Tessaract

    Tessaract Member

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    #15 Tessaract, Dec 2, 2019
    Last edited: Dec 2, 2019
    I agree with this. Having now actually examined the transformer spec sheet, I also agree that it would be wired in an autotransformer mode, where the transformer needs to transform only the power of the difference in voltage times the current.
    The first transformer would result in 208 + 208/240*24 = 228.8V, and you would draw 32 + 32*24/240 = 35.2 A from the 208 V supply. The second transformer would result in 208 + 208/240*32 = 235.7V, and you would draw 32 + 32*32/240 = 36.3 A from the 208 V supply. The power rating of the transformer would need to be (voltage increase)*(current drawn). Assuming max 32A drawn by car, then the transformer needs to be rated at a minimum of 887 VA. A 1 kVA rating is sufficient (but doesn't allow much margin).

    Only one transformer is required, since the HPWC allows neither of the two supply voltages to be neutral connections.

    A word of caution: any installation must use UL/CSA-listed components with code-compliant wiring methods and materials. For your own safety.
     

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