A lot of science goes into electric cars, but when it comes to gauging battery-charge percentage, there may be a little more art involved.

In this case, the DC quick-charge stations that are currently being installed near highways along the U.S. West Coast – and other locations – can't communicate with precision with electric vehicles to calculate the correct state of charge (SOC) percentages and will likely overstate the true amount of charge in the EV, according to one electric-vehicle advocate. And that could cause drivers to miscalculate their cars' available range and, well, come up short.

Tom Saxton, vice president of Plug In America, wrote on his blog about his experience quick-charging his Nissan Leaf at an AeroVironment DC Quick Charge station in Washington State. Saxton said that, charging at stations like the one he used don't know exactly how much energy is in the car's pack and so can display an almost 100-percent charge, but the true amount of energy in the pack can be closer to 80 percent. For a car like the Leaf with an EPA-rated 73-mile single-charge range, that could leave a driver about 15 miles short of his or her intended location.

Part of the issue is that when using a fast charger, a Leaf will only "fill up" to an 80 percent charge after starting from less than a 50-percent charge. This means that what appears "full" on the station doesn't mean "full" in the car, and there's no way to get the station to figure out what the actual situation is.

The solution? "Ignore what the station shows" and use the EV's on-board indicator to properly gauge the charge, Saxton writes.


I'm reporting this comment as:

Reported comments and users are reviewed by Autoblog staff 24 hours a day, seven days a week to determine whether they violate Community Guideline. Accounts are penalized for Community Guidelines violations and serious or repeated violations can lead to account termination.


    • 1 Second Ago
  • 24 Comments
      Joeviocoe
      • 2 Years Ago
      Reading the full article... wow ABG, you really did not get the point of it. Danny, I think you purposefully made it more confusing so that many would jump to conclusions that cause 100+ comment arguments. False conclusions like, the Leaf is the only EV affected, and the SOC meter on the Leaf is the problem. Danny, WTH man. Why do you put your own spin Saxton's article? He never even 'implied' that drivers could be stranded as you, ever so subtly put it... " that could cause drivers to miscalculate their cars' available range and, well, come up short. " and " that could leave a driver about 15 miles short of his or her intended location." NO, NO, NO! Tom Saxton does NOT suggest this. The vehicles SOC meter is clear as day as soon as the driver gets back into the car. The worst that will happen is that if a Leaf or iMIEV driver, after using a Blink or AV Fast Charger,... will get back to his/her car after leaving it charging for a while (coffee and snacks in hand)... and realize that, although the station says done, the car shows much less... and he/she must start a new charge cycle and wait. Here is the original article... it is worth the read. Especially since Danny's job is not to inform the public, but to incite argument for ad revenue. http://www.saxton.org/tom_saxton/2012/09/dcqc-soc.html Here is an even more concise article from Tom Sexton regarding fast chargers: http://www.saxton.org/EV/quickcharging.php And this is nice too, a bit more detailed about real world trips. http://www.saxton.org/tom_saxton/2012/06/dcqc-roadtrip.html Bottom line, Blink and AV fast chargers are piss poor designed to attempt to make charging easier for people by having their own SOC meter on the station itself. But SOC is a pain to measure even for the car. And although the Leaf can handle the "auto shut off" itself... the problem with these chargers is that they try to do it themselves. But this WON'T, CAN'T leave any EV drivers stranded as Danny implies. Just frustrated at having to sit a charger for another 20 - 30 minutes.
        jeffwishart
        • 2 Years Ago
        @Joeviocoe
        Retraction: CHAdeMo only calls for Wh remaining and Wh capacity to be sent to the DCFC, and the DCFC then divides them to get SOC. But your beef should really be with CHAdeMO for not having the vehicle send the SOC directly to the DCFC.
        jeffwishart
        • 2 Years Ago
        @Joeviocoe
        Your post seems to imply that the DCFC attempts to calculate/measure the battery's SOC. This is not the case. The CHAdeMO protocol calls for the SOC to be communicated by the BMS to the DCFC, and the latter is displaying the value, nothing more.
      • 2 Years Ago
      Silly article. 80% charge, actual charge, is a cap that Nissan put in to prevent damage to the battery pack. At that "pressure" (voltage) the battery cannot and should not be charged at 100%. However, obviously, from the point of view of the charger, the charge has reached 100% of its target where the target is communicated by the onboard car charger. It is just a matter of reading the manual and understanding this new technology.
      noevfud
      • 2 Years Ago
      Once the Actual LEAF SOC hits 80% during a QC session the temp curve changes radically and rises very fast and sharp. I would not charge a LEAF over 80% on a QC because of the high heat and degradation to the cells. Even though the QC current level drops significantly the last 20% it is still high and this is where you will age your pack. I have witnessed the actual pack temp rise at 80% even with a mild ambient temp and low pre-charge pack temp. Advising people to charge to 100% on a LEAF via a QC is bad advise because these temps are not visible on the LEAF instrumentation.
        2 Wheeled Menace
        • 2 Years Ago
        @noevfud
        If it's heating up during quick charging, then they have designed the current limit to be way too high. The sad truth is that as this battery ages, it's internal resistance will go up, and it'll heat up even more during quick charges, and be damaged even further. This effect will exponentially get worse. Going off everything i've read, and now this, i conclude that this battery pack was designed without any margin in the specs at all. It is not built to last. I hope the warranty is good on this car & that Nissan learns something - but surely they already knew that they were underrating things. It'd be hard to spend millions of dollars on R&D and not figure that out!
        Rotation
        • 2 Years Ago
        @noevfud
        The LEAF should measure its own pack state and prevent damage, including shutting off all charging (quick or no) if the pack gets too hot. I'm not saying it does, partially because I'm not a fan of the LEAF's pack, but it should.
        Rick
        • 2 Years Ago
        @noevfud
        Might be alright in Alaska, whats the heater like in the Leaf would it be any good for the cold weather climate? If the Leaf range anxiety suddenly decreased rapidly leaving you stranded not getting the stated milage when you started would you be a gonna at -40c in a Leaf in Alaska?
        • 2 Years Ago
        @noevfud
        The charger slows down after 80% and there is not an issue with battery temperature - the leaf also monitors the battery temperature and won't allow it to get out of bounds. One thing I have found with Blink quick chargers and the leaf is that pusshing the 100% override button will still only fill your car to 80%, but using the timer at 100% will allow the car to get to 100% every time. Not sure why that is, but I quick charge every day, and have verified this multiple times.
          • 2 Years Ago
          I've talked to several Leaf engineers on this point, and there's no danger going to 100% - the LEAF will limit the current to keep the battery temperature from rising - it just takes longer - for me to go from 40% to 80% takes about 15-20 minutes, but to go to 100% takes about 45 minutes.....
      JPWhite
      • 2 Years Ago
      I've noticed this behavior too. So if I want an 80% charge I select 100% at the EVSE. If I don't care I select 80% and typically get 65% or so. Once you know what the charger will do or not do you make accommodations. Fool me once shame on you, fool me twice shame on me.
        mustang_sallad
        • 2 Years Ago
        @JPWhite
        Blink EVSEs also allow charge scheduling, another feature that I think should be left up to the vehicle. These guys are enthusiastic about the technology, but they're overstepping their role!
        Joeviocoe
        • 2 Years Ago
        @JPWhite
        Why do Blink chargers try to do the "auto shut off at 80%" feature anyway? The car does it. The car knows best.
      SVX pearlie
      • 2 Years Ago
      Aren't EV packs supposed to "stop" at 80% SOC to maximize battery life? Along with never discharging below 20%? Isn't that the basic strategy to protect the pack from permanent damage?
        2 Wheeled Menace
        • 2 Years Ago
        @SVX pearlie
        Depends on the battery chemistry. Shallow cycles help with the lifespan for most chemistries. With others, a 100% charge, with a discharge down to 10% can wear on the battery a tiny bit more, by tiny i mean you are taking maybe 1/1000th off the battery's lifespan each time you do it.
      Rotation
      • 2 Years Ago
      That's bothersome if the QC stations can't communicate well. It is absolutely critical that a QC (unlike an EVSE) monitor the state of the pack and set its voltage/current correspondingly. If it doesn't know the pack state well enough to display it, does it know it well enough to charge the pack safely? With current Li-Ion pack technology, you can't really quick charge to 100% anyway. You just plain have to slow down at the 85% point or so. It's very hard to put the last 15% into a pack in less than about 45 minutes. So if the charger says it got you to 100% quickly, you can be pretty sure you should not believe it. My understanding is that some chemistries like LiFe-po can charge further before slowing down. But even it has to slow down at some point.
        jeffwishart
        • 2 Years Ago
        @Rotation
        There is a misconception about just what the DCFC can do that is quite pervasive. The DCFC has no control on the current being sent to the battery: the DCFC merely says what it can provide, and the vehicle's BMS dictates what is actually sent. Thus, the BMS is in complete control of the safety of the pack charging. So contrary to what is written in this article, it's not as if the DCFC "doesn't know" what the SOC is, it's just that the vehicle shuts the charge down at 80% if the SOC was below 50% at the beginning of the charge (the article gets this part correct later on).
          Joeviocoe
          • 2 Years Ago
          @jeffwishart
          Yes, I think the point of the original article was that the Blink charger does ALSO shut off the charging when at 80% (a default setting).. the problem is that the Blink charger "doesn't know the true SOC and has it's own way of guessing. So you have a overestimation happening by the charger.
          jeffwishart
          • 2 Years Ago
          @jeffwishart
          But the Blink DCFC does not have a default setting to shut the charge down at 80%. When you are setting up the charge at a Blink DCFC, you get a list of options of target SOC. It's true that on the first screen that 80% is the largest, and that to get to 100% you have to go to the second screen, but 80% is not a 'default'.
      goodoldgorr
      • 2 Years Ago
      Again, impossible problems with fast-charging.
      Seph
      • 2 Years Ago
      I think the title could use some editing, because it's inaccurate and ambigous.
        Joeviocoe
        • 2 Years Ago
        @Seph
        That's not a bug, that's a feature. Danny King's normal writing style.
      2 Wheeled Menace
      • 2 Years Ago
      Gee. Not hard to design a protocol that can communicate a target voltage, current limit, and voltage curve to SOC chart from the car to the station. An EE straight out of college could probably figure this out. Even Chinese engineers have figured it out in the eBike / eScooter world long ago. C'mon guys, this is not rocket science.
    • Load More Comments