• Aug 30, 2011
If you get enough like-minded individuals together, they can accomplish quite a lot. Take, for instance, a group of fans on the MyNissanLeaf forum who wanted a more accurate way to tell how much further they could drive their Nissan Leaf. They accomplished this goal by coding up a device that plugs into the OBD-II diagnostics port and returns the exact state of charge of the battery.

You might be wondering how that is any different than the existing state of charge meter on the instrument panel. Well, the problem with the OEM panel is that state-of-charge is shown as a 12-segement display on the dashboard. Since the Leaf's range can be anywhere from 47 to 138 miles, a single segment on the gauge could represent as little as four miles left. This lack of granularity can lead to some serious range anxiety when you are down to 1 bar and not really sure how much that bar means. Yes, there is the range output shown right besides the charge gauge, but that is only based upon your most recent driving habits, and only the driver knows what type of roads lie ahead.

With the new device, Leaf owners can see the exact state of charge as a percentage of battery life remaining, allowing them to extract every last mile without worrying about being stranded on the side of the road.


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  • 15 Comments
      2 Wheeled Menace
      • 3 Years Ago
      Cool. A voltmeter would do this as well. No device needed. Understand the curve of your battery and you will have a great idea of how much power ya got left..
        Rotation
        • 3 Years Ago
        @2 Wheeled Menace
        You can't measure state of charge in a Lithium Ion battery with simply a voltmeter. The main problem is a Lion has a very flat voltage curve. But beyond this, the voltage also fluctuates greatly with rate of charge or discharge. It even floats up and down with temperature and time and battery aging. It'll be higher if it was charged a few hours ago than if it was not, even if the actual state of charge isn't any different. Put all this together and trying to measure state of charge on a lithium ion battery with a voltmeter is very inaccurate, even if the lithium ion battery is completely disconnected (out of circuit/not under load).
        EVSUPERHERO
        • 3 Years Ago
        @2 Wheeled Menace
        HVH20 and Rotation you are wrong. 2WM is right. Not sayin that what you both say does not happen. But to say it is in accurate because battery use/wear and high curves and low curves on each side of the curve discharge/charge makes it hard to read range is wrong for two reasons. One battery wear on lithium's at least Kokam's is so gradual it makes no difference when looking at voltage. Two, you don't run lithium on the non-flat part of the curve, if you do you are asking for trouble no matter what you use for a gage. Of course the most accurate way is to count coulombs of electricity. Barring not being able to count coulombs, Amp hours should be counted. I believe Jack Rickard has arrived at AH as the most accurate way to know how much usable energy is stored or left in the pack. Only 80% DOD or 20% state of charge should be recognized as usable and stay on the flat side of the charging curve, only 5 miles or less is lost, by doing this on the top when charging and your batteries will last longer. As for telling if you have a bad cell, that should be entirely on a different meter that compares cells and alerts you if one is deficient. I would be happy with a voltmeter as 2WM says and a alert for a cell that deviates from the others by 10/100 of a volt.
          Rotation
          • 3 Years Ago
          @EVSUPERHERO
          EVSUPERHERO: It is precisely because you operate mostly in the flat side of the charging curve that page aging matters a ton when looking at voltage. The flat part of the curve is very flat. During a discharge, during the flat, part, cell voltage might drop from 3.85 volts to 3.75 volts. This is a drop of 0.1V. The difference between 80% charge and 20% charge is 0.1V. Now, over the age of your pack, it will develop a voltage droop of 0.2V or more under even the lightest loads (like say the headlights, or heater). So an 80% charged pack will now be below 3.75V, so it will appear to be actually less than 20% charged! A tiny change in voltage due to pack aging has made your voltage-based readings useless, they can't even tell 80% charged from 20% charged. You can't use voltage alone to measure state of charge on a Lion. Not even if you always do it under no load. In fact under no load is the worst case because every Lion pack of any state of charge will jump to 3.9V or higher if you just charge it for a few minutes. You have to load it for at least a few seconds to get the pack down to a voltage that makes any sense at all. You can see this on older cell phones by discharging the phone to 20% charge, then charging for 3-4 minutes. Immediately after disconnect the battery meter will read 50% charged or more, but if you just let it sit 30 minutes it will drop back to the 20% it is actually at.
          EVSUPERHERO
          • 3 Years Ago
          @EVSUPERHERO
          Of cours as Rotation points out you must look at votage when not under a load. It is very easy to coast and check the votage even on the hwy. I admit most people are to dumb to do this but it would present no poblems to me.
        HVH20
        • 3 Years Ago
        @2 Wheeled Menace
        Only if it was a lead acid battery pack. You can't do that with lithium based cells because if one drops out there is no way to detect it off pack voltage, at that point you've killed the car. The Leaf's SOC is based of counting the charge that flows in and out of the battery pack with respect to an estimated maximum for the conditions present - not total pack voltage. This looks like a cool little work around hack for the leaf to get the actual SOC % instead of the granular bars, but I wouldn't necessarily call it "designing a more accurate SOC" they are just displaying what Nissan is calculating. Honestly, it sells short the algorithms that they have spent decades perfecting which are far beyond the capabilities of home brew hackers.
      Michael Walsh
      • 3 Years Ago
      I have one of these. See pictures of it being built here: http://www.facebook.com/media/set/?set=a.10150275833929844.344867.704969843 and following the first firmware update, so that in addition to SOC in percentage and raw form it now shows pack voltage, amperage, and power/regeneration in kW: http://www.facebook.com/media/set/?set=a.10150295584434844.351023.704969843 I cannot tell you how much more confidence I have in the feedback the car is giving me. At least up to 20% charge remaining, which is as low as I've gone with it thus far - as Spec said, there is likely to be a more severe drop-off at some point under 20%, but I just don't know how far under yet. One of these days I'll run her down all the way to 0% remaining and find out.
      Spec
      • 3 Years Ago
      Yeah, they better be careful with that. Just adding more gradation doesn't help if it remains inaccurate. Creating very accurate state-of-charge meters is an extremely difficult problem. It isn't like gas tanks where you can just measure a physical liquid volume. The voltage drop curve for Li-Ions is notoriously flat followed by a severe drop-off. And there are many other factors such as temperature, voltage sag, etc. And then add in the fact that the way the battery operates will change over time as the battery ages. So Nissan probably intentionally makes it have few gradations.
      • 3 Years Ago
      I think it's great that the LEAF fans are able to come up with custom mods for the car. Good work on figuring this out. But honestly for me, I am fine with the standard battery charge gauge. It has enough detail for me and tells me how much charge is in the battery. But some people might not understand why I would want to upgrade the speakers in the car.. so I do understand the idea of customizing and making the car just the way you want it.
      Rotation
      • 3 Years Ago
      I don't get how a bar indicating only 4 miles per bar is lack of granularity. In the most straightforward fashion that's actually more granularity. For example, if each bar measures 4 miles, it's better granularity than if each bar measures 40 miles, right (i.e. you have only one bar)? The real thing is there are only 12 bars. So you only get accuracy to 8%, +/- 8%, regardless of total range. This is merely adequate. The range-adjusting digits are maddening. I only have personal experience with them in a Volt (I never drove a LEAF far enough to impact the range). But you can see it in the Car Show (on SpeedTV) review of the LEAF. The reviewer says the car has regenerative braking, and drives it down Lombard street and then points out he just got enough energy to go 4 miles from going down that street. This is complete nonsense, you don't get enough energy to go 4 miles from going down that 1 block of Lombard street. The energy recovered is only part of the equation, the bigger part is the car computer now thinks you'll be driving downhill for the rest of your journey, so each Joule of energy in the tank will take you further than it would have a minute ago when the computer thought you were going to be driving uphill for the rest of your journey, as you have to do to get to the top of a hill and then drive down it.
        Naturenut99
        • 3 Years Ago
        @Rotation
        I can agree with the bottom half... but not the first paragraph... The lack of "granularity" comes from there being only 12 bars for ranges of 47 to 138 miles. 47 / 12 = 3.91 miles per bar and 138 / 12 = 11.5 miles per bar. Thats about 7 miles diff. per bar. People dont want to assume that there are 11 miles left if there are only 4. Since the car is basing it on your most recent driving situation/behavior (along with state of charge) some would like a straight forward percentage of battery for those who can use that understanding better. Since the driver knows what roads and conditions lie ahead, those are capable of using a % better would like that info.
        EVSUPERHERO
        • 3 Years Ago
        @Rotation
        Yea Rotation, I explained the very same thing over a year ago on ABG. I imagine the Rav 4 EV drivers explained it 12 years ago.
      EZEE
      • 3 Years Ago
      Yay wide the hell open capitalism. Well, upgrading the meter...not the various incentives on the actual car.... But yay wide the hell open capitalism!
      goodoldgorr
      • 3 Years Ago
      It's about time then we got reports from the ones that got caught with a depleted battery, that find an occupied public charger and especially that needed to rent a second car or borrow another car because they knew that their ride was too long for their battery car.
      paulwesterberg
      • 3 Years Ago
      Nissan should release a software update where they shorten the top bar to indicate a partial bar. That way you could see when you have 4 bars, 3.75 bars, 3.5 bars or 3.25 bars and it would be no big shocker when you drop down to 3 bars.
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