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Nema 5-20 is somewhere between 33% and 70% better than 5-15

Discussion in 'Model S: Battery & Charging' started by scottm, Feb 20, 2015.

  1. scottm

    scottm Active Member

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    Who cares! It's all slow right?

    I ordered the 5-20 adapter and put it to task today on my mobile charger at work where I plug in all day. The only way 120V makes any sense at all is if you have loooong charge times, where the car is doing nothing else anyway.

    I think someone has pointed this out already... but they were saying there's a fixed minimal overhead that does not go toward charging, and once you get over that, the rest goes towards charging the pack. So you effectively get more than what the 33% would suggest by going to the 5-20 adapter.

    Here's my data points:

    Power math suggests Nema 5-20 at 120V*16A is 33% more Watts than Nema 5-15 120V*12A... (set maximums allowed per adapter type).

    Yet, the car reports 9 kmh charge rate on the 5-20 versus 6 kmh charge rate on the 5-15. Which is a 50% improvement, at face value.

    If you "pessimistically de-optimise rounding", to say maybe a true 6.4 kmh is being reported as 6, and only 8.5 squeaks out of the 5-20 but shows up as a 9... then we're sitting at the 33% improvement which is closer to what the power math suggests.

    If you "optimise rounding" say 6 is really 5.5 and 9 is actually 9.4, then there's an argument for the Nema 5-20 being a 70% improvement.

    My REALITY is estimated range is climbing at 9 per hour on Nema 5-20. And it was pretty close to 6 on 5-15.

    So I'm seeing close to a 50% charge improvement for a plug that is taking on 33% more juice. Which seems like a good payback. Charging at a higher power is more efficient, people have said this time and time again. It's true.

    It all boils down to this: I used to charge all day and get a free return trip home (replenishing at work what it took to drive there). Now a round trip commute costs me just 25% of the total distance travelled. Which is a 50% savings at home on the e-bill for the commuter portion. The adapter pays for itself in 7 months if used for nothing else, at my electricity rates and what the adapter cost me. Both of which are so little ... it's a fun fact not a business case.
     
  2. Cosmacelf

    Cosmacelf Active Member

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    The number I use is about 43% faster. Bottom line, if you have access to a 20A 120V receptacle, get the NEMA 5-20 adapter, it makes a significant difference.
     
  3. santana338

    santana338 Member

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    I just got one of these this week. I haven't used it yet but there are times when I park in a garage and the only option is a 5-20 plug. I used to get 3-4 mph or charge with the 5-15. I'm hoping for better with the 5-20 to give me more margin for my return trip. Glad you brought this up.
     
  4. Xenoilphobe

    Xenoilphobe Active Member

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    My garage at work has this option - just ran out an changed to this plug to give it a try this week...
     
  5. cantdecide

    cantdecide Member

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    We've noticed the difference is better than linear... However we primarily got ours as a just in case rather than money saving... If you get an extra 8 miles of charge per work day it can take a full year just to pay for the adapter depending on the cost of electricity.
     
  6. Cyclone

    Cyclone Active Member

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    I am confused. While I have 20A outlets that accept the t-style plug, they all accept that standard double-vertical plug. Is there any reason to get a t-style adapter rather than plugging into a 20A outlet and dialing up the amperage for the charge on the car?

    Note, I do not have my Tesla yet, so maybe I missed a nuanced point.
     
  7. RiverBrick

    RiverBrick Active Member

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    If you use the Tesla 5-15 adapter, it will not allow you to select more than 12 amps, so you need the 5-20 adapter or another solution to get the full 16A.
     
  8. Cyclone

    Cyclone Active Member

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    Thank you RiverBrick, that would explain the confusion!
     

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