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NEMA 5-15P to 5-20R adapter first use report - quite useful!

Discussion in 'Model 3: Battery & Charging' started by eprosenx, Jul 16, 2018.

  1. eprosenx

    eprosenx Active Member

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    So someone else mentioned this plug adapter in the forum the other day and so I went ahead and bought one. It allows you to get a NEMA 5-20 adapter for your UMC and plug it into this, and then plug this into a NEMA 5-15 receptacle.

    First of all- This is NOT UL or NEC rated for what I am going to describe here. Use this information at your own risk! While the adapter does carry a UL rating, it is stamped saying not to use it over 15a so my use case is in violation of that.

    This could be dangerous in the wrong hands! Basically the UMC adapter for a 5-15 outlet signals the car to max out at 12 amps. The 5-20 one lets the car draw up to 16 amps (the 80% derate of a 15 or 20 amp circuit respectively).

    Please do not try to use this to draw more than 12a on a 15a circuit!

    So the use case here is that you have a garage that has standard 5-15 receptacles all over the place (but they don't have the sideways notch that makes them also 5-20 receptacles). They are however backed by 12 gauge copper and a 20a circuit breaker. The only thing limiting you is the danged receptacle.

    In my own personal garage this was the case, and so I just swapped the receptacles out to ones that could do either 5-15 or 5-20 (though I charge my car off a HPWC anyway).

    Over the weekend I was at a friends vacation home where I had no good charging options. After some investigation, I found a 5-15 quadplex receptacle in the garage that was on a dedicated 20a breaker (intended for a freezer) and it had nothing else plugged into it. So I decided to try this adapter out. I was concerned that the receptacle was only UL rated for 15 amps and this adapter was only rated for 15 amps and so for the first couple hours I came out and checked it for heat with my hand every 15 minutes or so. It ran barely warm to the touch (some warmth is always expected).

    Note that I was concerned at first when considering using this that perhaps the 20a blade was thicker/larger/had more metal than the 15a one, but then I realized the neutral (current carrying) conductor was identical for 15a or 20a. I also was worried about the receptacle in the wall might not handle it, though at some point someone linked to a teardown of one manufacturers 5-15 receptacle and it had the same guts in it as the 5-20 one (just the plastic on the receptacle blocked you from using the horizontal slot unless you paid for the overly expensive 5-20 receptacle). YMMV though...

    The net-net is that I got 33% faster charging by being able to charge at 16a instead of 12a. It actually is probably more than a 33% gain since the fixed losses of running the cooling pump and such are the same either way.

    Thought this might be useful info for others! But PLEASE be careful. I controlled for risks by using a circuit finder to figure out which breaker fed this, I removed the breaker panel cover and verified conductor gauge, I also removed the receptacle and verified the wiring was secure and not daisy chained on elsewhere. Then I only ran this way during waking hours and I regularly checked the warmth manually. I also had a fire extinguisher readily available.

    Note that in theory there are thermistors in the UMC adapters to monitor receptacle heat. This likely defeats that safety mechanism to some degree as well.


    5-15to5-20.jpg

    https://www.amazon.com/AC-Connectors-Household-T-Blade-Adapter/dp/B017EUTHC0/

    5-15to5-20UMC.jpg
     
  2. davewill

    davewill Member

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    If it's actually a 20a circuit, I would just change one of the receptacles to a 20a one. Not saying the adapter isn't handy, but if I don't need to use it...
     
    • Like x 1
  3. eprosenx

    eprosenx Active Member

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    Yeah, I think I may add a 20a brand new duplex receptacle to my kit and just install as needed. (though the question is Decora style or old style?)

    In this case the decor in this house was all black outlets, so I won't be stocking those in my car (they are probably special order anyway).

    Also, many folks may not be cool with me modifying their electrical system. ;-) Just plugging in is one thing...
     
  4. davewill

    davewill Member

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    I thought this was in your own garage. Yeah, I wouldn't modify someone else's outlet.
     
  5. mknox

    mknox Well-Known Member

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    I bought this guy instead. Same idea, but I use it with the old-style UMC that has the adapter right at the plug end. I found the plug adapter made it stick out of the wall too far and it would pull down and part way out of the plug under its own weight.

    I sold my 5-15 adapter and newer replacement UMC when I sold my Model S, but kept the original UMC and 5-20 adapter that I had purchased separately. I use it to charge my new Model X from 5-15 sockets (dialed down to 12 amps, of course) when I travel. (New-style UMC that came with the car is at home).

    61m465TRv8L._SL1500_.jpg
     
    • Like x 2
  6. Rocky_H

    Rocky_H Active Member

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    Yes, I got that one too, for the same reason, so it wouldn't have a big weight sticking out putting so much torque on the outlet.
     
  7. eprosenx

    eprosenx Active Member

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    Lol, yeah, note that I have it sitting on a trash can in this picture. Definitely important to have strain relief!

    I bought the first one I came across on a whim. The one with the short cord as pictured above seems smarter. (though I still would not want to just dead hang the UMC from it without it being a 90 degree connector - also the temp probe in the end of the UMC adapter may have less ability to help if the end of that 6 inch cord was overheating).
     
  8. gjunky

    gjunky Trifecta: Solar and both cars are EVs

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    Isn't this all a bad idea? You are charging at 20A from a 15a circuit.

    I wish the 5-20 adapters were a little cheaper though (for the old UMC). I don't even think those are available anymore. We have 5-20s in the garage at work.
     
    • Disagree x 1
  9. eprosenx

    eprosenx Active Member

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    No. I am charging 20a (well 16) on a 20a circuit. The breaker and the wire are rated for 20a. It is just the receptacle I am plugging into (and my adapter) that technically are only rated to 15a (12a continuous).

    So to be clear, this is violating the ratings, but there is no risk of the wire in the wall or the breaker being the issue.
     
  10. mknox

    mknox Well-Known Member

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    In my case, no but I do have to remember to dial the car back to 12 amps when I use it.
     
  11. gjunky

    gjunky Trifecta: Solar and both cars are EVs

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    Good but then there is no benefit over using a regular 5-15
     
  12. mknox

    mknox Well-Known Member

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    None at all. It's just in my case, I don't have a 5-15 adapter with that UMC set. The converter cable that lets me use my 5-20 on a 5-15 outlet was a lot cheaper than buying the Tesla 5-15 adapter.
     
  13. gjunky

    gjunky Trifecta: Solar and both cars are EVs

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    That makes perfect sense. I thought the 5-15 came standard and you specifically bought the 5-20 adapter for this purpose.

    Just wanted to warn people not to use standard household outlets with the adapter as these outlets are not rated for 20a.
     
  14. mknox

    mknox Well-Known Member

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    Yeah, for reasons explained over here, I sold the original 5-15 adapter that came with the UMC and only have a 14-50 and 5-20 with this particular set.
     
  15. SigNC

    SigNC Member

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    I could also see this being of use when plugging into an external outlet that has a weather cover that makes the UMC hard to plug in.
     
    • Like x 3
  16. eladts

    eladts Member

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    Would it it be better to just buy another NEMA 5-15 adapter ($35 for v2, $45 for v1) instead of using this convoluted solution?
     
  17. mknox

    mknox Well-Known Member

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    Couple of reasons: In Canada, the 5-15 adapter is $60.00 vs. $4.49 for the dogbone adapter. Also, where I use the UMC it is a tight fit to get the plug into the outdoor receptacle, and I often have the problem of the weight of the old-style plug/adapter pulling out of the wall under it's own weight. 2 birds with 1 stone.
     

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