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240v/20amp HPWC how many miles per hour

Discussion in 'The UK and Ireland' started by cubbie, Aug 9, 2017.

  1. cubbie

    cubbie Member

    Joined:
    May 24, 2017
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    Location:
    ESSEX
    Just had fitted my HPWC for my new Model X being delivered later this month. There is a 20amp fuse the Hpwc is linked to. I only do about 50 miles a day so don't need a high charge rate. Would anyone be able to tell me how to calculate the miles I would get from a 20 amp breaker. Also what would I get from the UMC lead
     
  2. lbzbean

    lbzbean New Member

    Joined:
    Jul 11, 2017
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    3
    Location:
    UK
    I have my HPWC on the 20 amp setting. It gets 11-12 miles per hour on my S85.
     
  3. cubbie

    cubbie Member

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    Location:
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    Many thanks
     
  4. MorrisonHiker

    MorrisonHiker S 90D 2017.34 2448cfc

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    You can get a good estimate by taking amps * .8 * volts/330 Watt hours/mile. The .8 is because you can't use all 20 amps for continuous loads in the US. I suppose it could be different in the UK.

    So 20 * .8 * 240 / 330 = 11.6 miles per hour

    You can tweak the voltage number (since you probably won't be right at 240) and the Watt-hour/mile number to get a more accurate estimate but that's the formula you can use to get a good idea. Of course the X will have a larger number than the S so you would get fewer miles per hour of charge. I'd think you'd still get close to 9-10 mph.
     
  5. arg

    arg Supporting Member

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    Aug 22, 2012
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    Location:
    Cambridge, UK
    Yes, in Europe breakers are rated for continuous load and there isn't a 20% de-rating rule (we have a 'diversity' calculation for if the load is less than continuous, so everything comes out much the same but things are just labelled differently). So the HPWC on 20A setting will draw 20A and that's OK on a 20A circuit. That circuit can't be shared with anything else however - if you've got for example a 20A circuit feeding your garage with lights etc. in there as well as the UMC, the maximum you could have for the UMC would be 16A.

    When charging at very low currents, there's an extra factor in the calculation given above: the car uses a certain amount of power just to be "on" and ready to charge - as a rule of thumb, about 1A is 'wasted' hence the step up from 10A (UMC on domestic 13A socket) to 20A on the UMC will be a bit better than double - more like 19/9 = 2.1 times as fast.
     
    • Informative x 2
  6. cubbie

    cubbie Member

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    Many thanks for your reply
     

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