Fast Chargers Proliferate For Nissan Leafs, New Etiquette Issue Arises

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Polar Charging Post and Nissan Leaf

Polar Charging Post and Nissan Leaf

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You'll often see an "80 percent" metric used when discussing electric car charging at a fast charger.

There's a very good reason for this: While that first 80 percent may fly by in only a quarter to half hour, the last 20 percent takes one heck of a lot longer.

It's that last 20 percent that is now causing tensions between some electric car owners, and bringing up questions of etiquette when using a quick charger.

Do you hang around and hope to top up those final few percent before the next electric car owner wants to plug in? Or do you accept that charging past around 80 percent may see you there for another hour or two, and move on to let other owners top up?

Leaf drivers on the SF Bay Area Nissan Leaf Owners group on Facebook are leaning towards the latter.

The issue is that fast chargers are set to gradually slow down once that 80-or-so-percent mark has been reached, to prevent the battery from overheating.

This is fine if you only need to top up your battery, but causes an problem for those looking to squeeze every last kilowatt into their battery pack--particularly if there's a queue developing behind them.

In effect, it's a similar issue to fully-charged electric vehicles plugged in at regular charging spots preventing others from using them--or plug-in hybrid owners occupying spaces that might be needed by full-EV cars with no secondary power source.

Various solutions are suggested on the Facebook page, including setting fast chargers to stop at 80 percent to encourage users to move on quickly afterwards. Another user suggests a 15-minute cap--after 15 minutes, drivers can decide whether they really need another 15 minutes, or whether that's sufficient to get them to their next destination.

There are some good ideas rolling around, but ultimately it comes down to etiquette. Don't need those final few percent? Unplug and let someone else use the station...


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Comments (27)
  1. The charging station idea is fraught with issues like non-EV drivers parking and EV drivers hogging the spaces after charging is completed. Good luck finding an empty spot.

  2. Charging to just 80% is good for battery life. Stop there if you don't need the additional range immediately, but go to 100% if you do.

  3. Yes and no. You can charge past 80% with little damage, (according to Tesla) but definitely avoid charging to 100% unless you must get every last mile from your pack.

    I don't know about you, but I always like to charge to "full" or whatever the highest non-detrimental charge is if I'm plugged in. Might as well.

  4. I was thinking more of my Leaf as that's what Nissan recommends, but I routinely charge my ModS to 90% which is a "standard charge" 238/265 rated miles.

  5. Indeed LiIon batteries age faster while at high SoC -- but only for as long as they are kept up there.
    There seems to be absolutely nothing wrong with charging to whatever Nissan or Tesla label 100% if that energy is used soon afterwards.

    @Joshua, there is no hard "detrimental" vs "non-detrimental" threshold.
    Letting the battery sit most of its life at 100% SoC is obviously not great, 90% already less bad, 80% even less, 60% getting quite good, 40% maybe ideal...

  6. As the battery pack reaches a higher state of charge (particularly SoC above 80-90%), the internal resistance of cells increases. Increased resistance means more internal heat generated. Reducing current (Leaf), or active cooling (Model S, iMiEV) keeps the pack from getting too warm. Listening to An iMiEV quick charge makes this connection very clear (audial indicator) as AC compressor ramps up with increasing SoC.

  7. Brian, your statement about internal resistance increasing with SoC goes against my understanding on Li-ion chemistry, so maybe I need to revisit the topic.

    I'm curious where you got that information. Do you have any kind of source or reference I could study a bit?
    Thanks in advance

  8. There is also another issue here: It's not that nice to the battery pack. After making a long-distance trip from one side of the UK to the other (270 miles or so) with five rapid charges in 85-88 degrees F heat, my car's battery pack peaked at 120 degrees.

    The majority of the heating didn't occur when driving: it happened when quick charging the battery pack beyond that 80 percent.

  9. Hmm, there is no reason inherently for LiIon to heat up more during one part of the charge versus another. Its internal resistance stays roughly constant, so if anything it should heat up LESS during those top 20% as charging current drops.

    Just curious, how did you come to the conclusion that most heating occured at the end of the quick-charge?

  10. Not quite. The internal resistance to charging goes up as the SoC increases. To overcome this you need more voltage, but LiIon gets damaged above a certain voltage. Since you can't increase the voltage, the quick charger has to slow down. It eventually drops to 1kW, then stops.

  11. Er... I was talking about electrical resistance (or impedance; same in this case), in Ohms. For the Leaf pack, it's in the 80~100 mOhms range. This does not change in any meaningful way with SoC.

    LiIon charges at constant voltage (4.1V/cell for the Leaf NMC, up to 4.3V for cellphones LiCo), with current limiting (125A for the Leaf, temperature-dependent); current naturally drops as max voltage is reached.

    LiIon has great coulombic efficiency (98+%), so quick-charging losses are mostly due to internal resistance. The resulting heating increases with the _square_ of the current.

    Temperature should therefore rise much _slower_ at high SoC, not faster.

    Surprisingly, Nikki states the opposite, hence my question. Has anyone actually measured?

  12. If I have to guess, I would say that due to the consecutive driving sesssion and quick charging session, the longer you charge, the hotter it gets until the heat produced from the charging is lower than the amount of heat the pack can dissipate especially with high 80s temperature already. I think Nikki just happened to observed the temperature rise due to the longer stay at the quick charger. The majority of the heat could have been produced in the first stage (less than 80%) of charging and end up reflecting in the time frame of the second stage charging (> 80%, < 97%).

    Where is the Leaf temperature sensor located? On a particular cell or averaged across several cell or inside the pack or on the casing? What is the thermal inertia?

  13. Charging posts should have a keypad on them for cell phone number input or users could have a registered magnetic ID fob...the charging post could also have queue button; when the car reaches 80% and someone has pressed the 'queue button' the charging post can text them to tell them to move their car so the next user can plug in. I recall leaving a charging post in my Volt...there was another Volt parked beside me and plugged into the 120V outlet. I unplugged their 120 and popped in the 240 for them as a courtesy.

  14. Tesla SuperChargers solves this eloquently… two Model S share a charge station, as 1st EV ramps down (reaching fuller SoC), the 2nd one ramps up current. From engineering point of view; lower current at higher/lower SoC is good for battery life cycle, with fastest charging occurring mid-SoC.

    Tesla is doing an excellent job monitoring and responding to demand. At Gilroy, CA (just south San Jose), the 4-charge-point station is being expanded to 14 charge-points. Theoretically, the Gilroy station can charge over 500 Model S's per day (14 plugs x 2 EVs/hour x 18 hours/day … ignoring demand between 11pm & 5am)

    Not to be critical of other charging infrastructure deployments, but some lessons can be learned from the Tesla SuperCharger team. :)

  15. I wonder if/when someone will put in a L3 charger for non-Tesla there. A combo CHAdeMO/Frankenplug charger that charges a per-minute rate would do well there.

  16. ECOtality (Blink) and Chargepoint already have the customer's contact info, and require a registered RFID card to activate the chargers. For ones like Eaton that have no RFID reader, this would be necessary.

  17. Don't charge for electricity, charge by time. Also, if you're not plugged in, you are ticketed or towed.

  18. This is all very interesting, but if you live in an area that has NO fast charge infrastructure, it's not even a consideration. Also, if you live in an area in which temperatures can be above 100 degrees for 30 days at a time the battery cells can't even handle charging to 80% without degrading.

  19. Battery swapping is the only real solution. Even the fastest chargers are too slow.

  20. Isn't this the result of limited range and/or range anxiety?
    In some way, it is also the fault of "FREE" charging. Start to charge money for it and it will change.

    Charge by KWh in the first 20 mins, then by time. For every 20 mins after that, the cost doubles... (This is DC quick charger only). Only those who really "need" it will pay for it.

  21. I like this idea. It will encourage people to charge up and go. You may have to add a 'demand charge' extra to compensate the owner for charge-ups that occur between 1-5pm (Peak Demand time in most areas).

  22. I charge to 80% at the public super charger and then plug in at home overnight to top off. Works for me.

  23. Unfortunately, as anyone who has driven an EV (car) for any significant period of time will know, much of the benefit of having one is the ability to precondition the vehicle prior to use. If you are not still connected to the mains, the power needed for this comes from your battery, reducing range and aging it unnecessarily. The only answer is for at least every other parking space to be equipped with a charge point. Either our respective governments are serious obout EVs or they are not. If they are then they need to spend some cash to properly make it work. I am not suggesting expensive EVSEs popular at the moment. Just a simple GFI-protected weatherproof mains socket like the ones used for block heating would do perfectly well.

  24. I agree with that but the EVs shouldn't be preconditioned on DC quick chargers...

  25. The solution is to add more chargers or develop better batteries.
    Browbeating owners trying to charge their cars or forcing them to
    accept a smaller driving range when what they have is almost always insufficient is out of line. EV owners never blame their cars for anything, no matter how much inconvenience they cause them.

  26. Don't ever discuss this point with EV Enthusiast or any hardcore BEV fans. They will argue with you to "death" by telling you that the current BEV offering is "good enough" for everyone.

  27. As EVs become more mainstream I think you will have to rely more on programming of infrastructure and less on etiquette. Early adopters tend to be more friendly to other EV owners than you generally experience between gasoline car owners. It's just a matter of time until the first road rage incident occurs at a charging station and someone gets strangled by a charge cord!

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