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Slow-down or Stop at Level-2 Charger?

Discussion in 'Technical' started by gavine, Sep 23, 2016.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

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    I often wondered, if in a close-call situation regarding remaining range, would it be better to slow-down or stop at a Level-2 charger. I decided to do some quick math, realizing that there are lots of variables that I didn't consider, but generally speaking, it seems slowing down is about equal. Here's the math (or maths if you're from the UK):

    Let's assume an S75D can go 225 miles at 75MPH. Sound about right? That would be 3 miles per kWh (225miles/75kWh). At 55MPH, the car should be able to go 335 miles which would be 4.46 miles per kWh (335miles/75kWh).

    Let's say you have 75 miles remaining on your trip but only 17kWh of battery left. Going 75MPH would take one hour to arrive, but would require 25kWh of energy (75miles/3miles per kWh). You would have an 8kWh deficit. At a 30A/6kW Level-2 charger, those 8kWh would take about 1.33hrs (8kWh/6kW).

    Going 55MPH would require 16.8kWh (75miles/4.46miles per kWh) but would take 1.36hrs to get there (75miles/55MPH).

    Therefore, it seems that slowing-down from 75MPH to 55MPH in this case would be about equal, notwithstanding the extra time to pull over, plug-in and get-back on course.

    As much as this was a specific set of circumstances, I think it generally applies to most situations. If you can still make it by slowing down a reasonable amount, it pays to do that vs. stopping at a standard Level-2 charger. Of course, if you need to stop anyway, then charging is a better option, but if time optimization is paramount, it looks like a tie.

    Moral of the story, if you need more range, slow-down, unless there's a Supercharger en route. But, if you don't want to slow down, stopping at a Level-2 is about equal.
     
    • Informative x 1
  2. aesculus

    aesculus Still Trying to Figure this All Out

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    This is a big part of the equation. Also finding the charger, setting up payments etc can all add into the time too.

    Just easier to slow down. And if it looks like you are making progress, you also have the option of immediately increasing your speed again.
     
  3. kort677

    kort677 Active Member

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    I would slow down, excepting if I planned to charge overnight
     
  4. NeilErdwien

    NeilErdwien Member

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    Am I missing something?

    At 75MPH, the total trip time would be 1 hour driving time (75 miles/75MPH) *plus* the 1.33 hours charge time (8 kWh/6 kW) -- for a total time of 2.33 hours.

    Doesn't slowing down win by a landslide?
     
    • Like x 2
  5. Saghost

    Saghost Active Member

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    Yeah, that's what I was thinking. at 6 kW, it's well over an hour of extra charging, plus the hour of drive time.

    Of course, that's one specific scenario, but it's probably generally applicable if your only charging options are 6 kW Level 2.
     
  6. gavine

    gavine Petrol Head turned EV Enthusiast

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    You're RIGHT. I was just making sure you were paying attention. :oops:
     
  7. NeilErdwien

    NeilErdwien Member

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    I'm right? I've gotta show this post to my wife. :)
     
    • Funny x 3
  8. NeilErdwien

    NeilErdwien Member

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    She said something about a stopped clock -- and then I stopped listening. :)
     

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