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Does my MPPT SCC and 120V charger choice make sense for my LiFeMnPO4 batteries?

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  • #91
    I have read a lot of Maine Sail's posts but had not seen that particular one. I am very familiar with the temperature-related aging as I was able to access and read battery stats from my Nissan Leaf and could see the effects of our hot summers on that car's battery capacity. Unfortunately this van will be stored out in the sun in 100+ degree weather at times, nothing I can do about that. I used similar charging practices with my Leaf to what you described for my camper van--I rarely ever charged the car and left it at a high SOC.

    The van will be used roughly every-other weekend and one trait I really like about LiFePO4 is the fact that I can bring it home with a partial charge, park it (for a week or two) and not worry about keeping a lead acid battery topped off. I will likely shut off everything when it's parked and turn it on a day or two before a trip to 'fill' the battery. If I had a boat that sat for months I probably would do the very low voltage float you suggested.

    At the end of the day, it's just a battery and I plan to use it. I like learning about technology, hence this thread. But as stated, one challenge I'm finding is the two different charging devices produce fairly considerably different SOCs based on the path taken to reach that target voltage (charge rate, time, etc).

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    • #92
      I would be interested to know some details of your Leaf battery capacity change with time and temperature.

      As far as I can see within reason it is not so much the SOC that the battery is charged to but how long it spends at that SOC and whether or not there will be loads on the battery that are the important factors.

      Simon
      Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
      BMS - Homemade Battery logger github.com/simat/BatteryMonitor Latronics 4kW
      Inverter, homemade MPPT controller

      Off-Grid LFP(LiFePO4) system since April 2013

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      • #93
        Originally posted by karrak View Post
        I would be interested to know some details of your Leaf battery capacity change with time and temperature.
        I will start by saying the Leaf was a great car and although there was a capacity loss as measured through a bluetooth OBDII reader and the app "Leafspy," the range loss was not noticeable. It seemed to go just as far on a charge and used the same percentage of the battery on my daily commute that it did when new.

        In logging the amp-hours every couple of weeks over 3 years (my lease length) it lost 9% of the total amp-hours. In the winter time, and particularly when it first turned cold, there would be a slight temporary amp-hour loss, but that capacity came back as the temperatures came back up. However in the summer in northern California, temps are often over 100 degrees. It seemed to loose all of its capacity during those 3 hot months. In other words, it lost about 3% of its capacity from the beginning of summer to the end (permanent loss), each year, and losses during the winter were temporary and generally restored when temps came back up.

        Leafs do not have a temperature controlled battery. Based on my results with the car I wouldn't want to own one longterm in a hot climate unless the battery were temperature controlled or the battery chemistry improves to the point that summer degradation is reduced. I actually have a deposit on a Tesla Model III, but likely won't go through with it only because my life circumstances have changed since I put down the deposit. Electric drive is fantastic.

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        • #94
          Thanks, interesting information. Three percent per year is a little alarming. They are supposed to have improved the batteries, having a look at what the latest warranty has to say should show if this is the case. I am sure that there are many more improvements in lithium ion battery technology yet to come.

          My friend's LFP based off-grid system that I designed and built spent its first three years on the north wall (in the southern hemisphere) of an uninsulated dark blue tin shed where the temperatures would have been above 100F on a regular basis in summer which caused me some concern but at the end of this I tested one of his cells and it still had its rated capacity of 90Ah. This is the cell that I did the charge/discharge tests on. It is quite possible that it had more than 90Ah when new and I would be surprised if it hasn't lost some capacity. My guesstimate is that our batteries are loosing between 1%-2% PA, probably closer to 1%. It will take a few more years of monitoring to get a better idea.

          Simon
          Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
          BMS - Homemade Battery logger github.com/simat/BatteryMonitor Latronics 4kW Inverter,
          homemade MPPT controller
          Off-Grid LFP(LiFePO4) system since April 2013

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          • #95
            A LEAf battery is not LFP or really anything close to it. One reason commercial EV manufactures do not use LFP batteries is because they cannot easily control SOC. No commercial EV manufacture allows the customer to fully charge the Traction Battery. They could not offer or honor any warranty if they did that. The Leaf uses NMC, and unlike a LFP battery has a very defined Charge/Discharge curve. I use them in my racing golf cart as many DIY EV builders now use Leaf, Volt, and Tesla packs because there are so many used EV's out there collecting dust no one wants. Other source is salvaged yards which is where I look to get the newer models after 2012 failures.

            WIW Nisan limits to 10/90. Nissan limits charge voltage to 4.1 vpc, full SOC is 4.3. On the discharge side has a few levels

            Charge Terminate at 4.1 volts.
            Very Low at 3.625
            Limp Home or Turtle Mode at 3.22
            Call Tow Truck or Shutdown at 3.2
            Destroyed at 3.0 volts.

            They will never let you go to 4.3 volts (100% SOC) or 3.0 volts (0% SOC). My controller is set to Float at 103 volts, and Motor Controller LVD at 90 volts. I run 25S aka 96 volt battery @ 66 AH

            See that nice Slope. It is not FLAT like LFP. Makes it real easy to charge to any SOC you want.
            Last edited by Sunking; 06-23-2017, 05:42 PM.
            MSEE, PE

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