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100' 110v extension cord - 10 gauge or 12?

Discussion in 'Model S: Battery & Charging' started by Stimyg, Apr 28, 2013.

  1. Stimyg

    Stimyg Member

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    My car is on its way! I'm thinking I should carry around a 100' 110v extension cord for when I stay overnight at friends houses. I'd prefer to go with the 12 gauge size, just so it takes up less trunk space and I'm carrying less weight around. But would I be better off with the 10 gauge? (Been looking at the 'yellow jacket' cords on amazon, seem good.). Thanks.
     
  2. drees

    drees Active Member

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    The general rule of thumb is that you want to keep voltage drop under 3% and to do that charging on 12A, you'll need 10 AWG for 100 ft. You may also be able to charge at 16A (20A outlet) in which case you'll definitely want the 10 AWG cable - even there it's slightly over 3% voltage drop for 100 ft.

    Personally I prefer the flexibility of having multiple shorter cords over 1 long cord. Most of the time you don't even need more than 25 ft.
     
  3. deonb

    deonb Active Member

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    How? Does Tesla now have a NEMA 5-20 plug available? Or announced that they're coming out with one?

    If this is the case, then I would agree with 10 AWG. Although then you would need to get a NEMA 5-20 extension cord which would become a pain for general use. Maybe rig up a male 5-15 with female 5-20 yourself.

    If not the case, then 10 AWG is a big thing to carry all the time for just-in-case. The charger will only draw 12 A over a NEMA 5-15 so 12 AWG should be fine (in theory 14 AWG could be fine if you start with a high voltage supply - but you can't know until you get there).
     
  4. cinergi

    cinergi Active Member

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    I've had no problems using a 50 and 25 foot 12-AWG pair of cables (75' total) ...
     
  5. Stimyg

    Stimyg Member

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    I'd prefer to go lighter if i can get away with it, since its only for occasional use. Is there a danger in using a 12 gauge at 100'? If its just voltage loss, what does that translate to in terms of charging time? Is there any difference between one long cord or stringing shorter ones together?

    Finally, is an average suburban home likely to have a 16amp outlet anyhow?

    thanks again.
     
  6. deonb

    deonb Active Member

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    No, it's not dangerous - the charger is rated from 100V to 240V. It will just charge a bit slower.

    Here is the theoretical range differences you can expect per 10 hours of charge on 110V, based on the voltage drop calculator on:
    http://www.powerstream.com/Wire_Size.htm

    Directly: 30 miles (for example - with 110 V it depends a lot on external factors like temperature etc).
    10 AWG: 29.4 miles
    12 AWG: 29 miles
    14 AWG: 28.2 miles
    16 AWG: 27 miles (however, 16 AWG may put you under 100V, so I would not recommend this one).


    As far as a 20 amp outlet is concerned (which gives a max of 16 amp on a 20 amp circuit breaker that trips at 80%), it's not too uncommon in a garage, which is probably where your car is likely to hang out. However, I don't know if this is material - I know of no (non-hacked) way to get the car to charge using 110V at more than 12A. I would love to be corrected on that if that is indeed possible.
     
  7. Cosmacelf

    Cosmacelf Active Member

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    Yes, using the standard Tesla 120V adapter, you can't charge at more than 12A.

    For the Roadster, Tesla makes a NEMA 5-20 plug (left blade is sideways) which allows it to charge at 16A, but they haven't made such an adapter for the Model S.

    Be careful about buying non-beefy extension cords. The Model S monitors how much voltage drop occurs as it ramps up amperage, and if it detects there is too much of a voltage drop, it will stop the charging session.

    120V household charging is a very slow charge. If you truly need to charge up a friend's houses, check to see if they an accessible dryer outlet. If so, you can plug into that using the Model S NEMA 10-30 or 14-30 adapters. But this supposes that the UMC cord can reach it 20 feet away. If you want to plug into these types of 240V, higher amperage receptacles more than 20 feet away, you'll have to make your own adapters and get a 50A NEMA 14-50 extension cord that they sell for RVs (these are REALLY beefy and heavy). I have a document that describes this in detail if you're interested: http://cosmacelf.net/Home%20Made%20Adapters.pdf
     
  8. markb1

    markb1 Active Member

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    I calculate that at 12 amps, over 100 ft, you'll lose 1.2V at 10 AWG, 1.9V at 12 AWG, and 3V at 14 AWG. Lots of houses have 14 AWG wiring in the walls (which is the smallest allowed for 15A circuits), so you may already be losing a few volts to that, anyway.
     
  9. richkae

    richkae VIN587

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    Remember to not leave it in a coil when using it. Spread it out a little.
     
  10. mitch672

    mitch672 Active Member

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    #10 mitch672, Apr 29, 2013
    Last edited: Apr 29, 2013
    I carry a 25' and 50' 12AWG extension cords, I also built a 25' 6/2 SOOW 45A rated cord terminated with 6-50 male/female, and then a short adapter to a 14-50 (for RV Park use), I used 6/2 instead of 6/3 to lower the weight (1 less #6 copper conductor), we don't need a neutral with 240V, just a ground. I also have the 14-50, 6-50, and 10-30 adapters (as well as the 120V) for the UMC... Yes, I was a boyscout (motto: "always be prepared")
     
  11. rolosrevenge

    rolosrevenge Dr. EVS

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    I'd use 10 AWG, you don't know what the household voltage levels you'll be plugging into. You may also want to dial down the current to only 12 A.
     
  12. drees

    drees Active Member

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    My calcs show voltage drops exactly twice as high as yours...
     
  13. markb1

    markb1 Active Member

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    #13 markb1, Apr 29, 2013
    Last edited: Apr 29, 2013
    Hmm.. I probably made a mistake. 100-foot cord is actually 200 feet of wire added to the circuit, so I think you're right.
     
  14. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    From the FAQ:
    FAQ: Home Tesla charging infrastructure QA

     
  15. JohnQ

    JohnQ Active Member

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    Was wondering when FlasherZ would join:smile:
     
  16. gnychis

    gnychis Member

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  17. wcalvin

    wcalvin Member

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    Limiting factors for 120v long runs

    I am currently charging from a 119 volt (no load conditions) receptacle in the far corner of our condo's parking lot, maybe 250 feet from the building. When the night lighting is on, it drops another volt.

    Under a 6A load from the Tesla, the voltage drops another 12 volts as if the wiring totaled two ohms.

    This takes the voltage at the car down to 106 volts. And that is about the limit because the inverter regulation typically gives out at 105 volts in the usual commercial gear. While I can charge at 8 amps, it doesn't last long before something trips and I have to walk down to the car and manually reset the charge max to 6 amps.

    I tell this story because keeping voltage above 105 v is what governs all of the extension cord use. To measure your series resistance and judge how another extension cord will affect it, measure the voltage without a load (the car's charging display will show that as the first voltage with zero current). The voltage difference between no-load and loaded, divided by the current, is the source resistance.

    If my source resistance were one ohm instead of two, a 12 amp draw would drop the supply voltage from 119 to only 107 volts and the Tesla inverter would not trip. But I am stuck with limiting the Tesla charger to 6 amps, and so have charging times twice what one gets from Tesla's calculator for 120 volts at 12 amps.

    So the lesson is that you can use various extension cords, so long as you reduce the charging current to keep the voltage under load above about 106 volts. Start low and increment amps until voltage drops to 106 volts. But there is a cost to using undersized extension cords, in the form of more heat generated along the wire.
     
  18. ToddRLockwood

    ToddRLockwood Active Member

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    A 100-foot 10AWG extension cord is going to be quite heavy. I'd recommend going with a 25 or 50-foot cord. I carry a 25-foot 10AWG in my car, and it's been adequate for every situation where I've needed it.
     
  19. dhrivnak

    dhrivnak Active Member

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    I have successfully used two 12 gauge cords 25 and 40 ft several times in my Roadster with no problem and we get to charge at 15 amps. ;) And for me two 50 ft cords are far better than a 100 ft one. Those are a real pain to roll up.
     
  20. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    If you look at American wire gauge - Wikipedia, the free encyclopedia, the resistance of #10 AWG copper wire is about 1 milliOhm per foot and #12 is 1.6 milliOhm per foot. That means that 100' of extension cord, 200' out and back, has a resistance of 0.20 Ohms for #10 and 0.32 Ohms for #12. Because Voltage drop is I*R, with a 12 Amp draw, you would get a Voltage drop due to wire only of 2.4 Volts for the #10 and 3.8 Volts for the #12 cord, both very reasonable. Power in the cord is I^2*R, or 29 Watts for the #10 and 46 Watts for the #12. Both are fine is the wire is spread out, but if you leave the wire coiled up (especially for the #12), its going to start getting warm. You don't have to completely unspool all of the wire, but just spreading out the unneeded length some (especially for the #12) is a really good safety practice.

    The place where heat can really build up is at the connectors. Two 50' cords are more convenient, but that setup adds one more set of connectors.

    Whatever you do, follow the safety practice of checking all connections and the wire in the middle to see if anything is getting uncomfortably hot. Comfortably warm to the touch will not start a fire, but it can take a while for large masses to warm up. Do this check a few minutes after charging starts and 15-20 minutes later. If anything is getting uncomfortably hot, fix it so the hot spot cools off, or stop charging!
     

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