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  • #31
    small LFP bank

    Originally posted by karrak View Post
    I agree with PNJunction that unless you have some electronic engineering experience you should start off with a small system like his. There are two reasons for this, the first being that if things do go wrong you won't loose too much money, the second and more important reason is that the larger the battery the more energy that can be released quickly if things go wrong and the more damage that can be done.

    Keeping an LFP battery safe and prolonging its lifetime is in my opinion more simple that keeping an FLA battery healthy. All you have to do is keep the voltage to any cell within the battery within the range of 3.6 volts to 2.5 volts. If you are charging from solar at a low charge rate the maximum voltage can be dropped to 3.45 volts or even lower if you want a longer life for the battery.

    As PNJunction suggests this can be achieved by keeping the SOC of the battery between 20 and 80 % which equates to a voltage range of 3.4 to 3.2 volts per cell (13.6-12.8 volts for a 12 volt system), or by utilising a larger SOC range of around 95 to 10% and using some sort of Battery Monitoring/Management system to make sure that any particular cell does not go outside the safe operating voltage range.
    Simon
    This is the strategy I've adopted in my grid-tie hybrid using a mere 100 AH of CALB LFP at ~48V since July 2015. Looking forward to someday increasing it, but, so far so good.
    inMichigan

    Comment


    • #32
      Originally posted by inMichigan View Post
      This is the strategy I've adopted in my grid-tie hybrid using a mere 100 AH of CALB LFP at ~48V since July 2015. Looking forward to someday increasing it, but, so far so good.
      inMichigan
      Hi inMichigan,
      Good to see someone else trying out LFP batteries. I am interested to know more details about your setup, in your album you mention a Flexmate80 solar controller and solar panels, how does this link in with your battery and the grid? I would also be interested to know what voltages and current you are charging your LFP battery with? DO you have any BMS of any description?

      Thanks
      Simon
      Off-Grid LFP(LiFePO4) system since April 2013

      Comment


      • #33
        Originally posted by karrak View Post
        Hi inMichigan,
        Good to see someone else trying out LFP batteries. I am interested to know more details about your setup, in your album you mention a Flexmate80 solar controller and solar panels, how does this link in with your battery and the grid? I would also be interested to know what voltages and current you are charging your LFP battery with? DO you have any BMS of any description?
        In general, the setup still looks like this:

        In September, the two GFCI breakers were moved from the right panel into the left panel as a gang of 4.

        All 4 of my FM80's are set up to Absorb/Float at 3.400 volts/cell. I sell at 3.341 volts/cell. Since, I'm grid-tie hybrid, I bounce between these two states each day. I chose these settings to avoid the knees. I don't need any load shifting. I don't really need or want to overwork the battery bank like an off-grid person would need. I absolutely know my 17 cells of 100 AH CALB are smaller than the manual would recommend. I also know the manual's guidelines weren't written for lithium. In forum space, I see a few lithium off-grid houses (like yours), I know of one on-grid guy in LA who load-shifts, and I haven't found another grid-tie hybrid (yet).

        Summarized here:


        Between OpticsRE, Wattplot & Excel, I can graph every which way, any particular questions?

        Originally posted by karrak View Post
        Hi inMichigan,
        DO you have any BMS of any description?
        I started out planning to use Mini-BMS with HomeBoard, contactor, etc... in fact, I bought the materials. I then decided to keep it simple--my choice. I decided the risk of the monitoring system (48->12V step down to feed the contactor) was adding more risk than I wanted, so, I decided to just trust the relay in the Radians to disconnect per it low voltage disconnect. Yes, I know that relays can fail. My thought is that to destroy the batteries, at a high level, I would need the relay to fail, the grid to go down, these two failures to happen after I've gone to sleep but not so close to sunrise that my battery bank can't sustain the house loads until the sun rises. I'm sure there are a few other rare but possible failures, in both the Outback side as well as any BMS side. So, bottom line, no automatic BMS for me. I write down setting changes in a log book. I do monitor the resting cell voltage with my Fluke.

        Since I'm running in hybrid mode, my battery bank essentially is mostly spending it's life in a partial state of charge. Now and then, I switch to grid-zero mode, limit the amp draw from battery bank (balance of the power comes from the grid) and dive towards 2.9 volts/cell while keeping track of amps thru the shunt (FN-DC). Yes, I know that voltage & SOC while under load is not reliable. Each evening & thru the wee hours during test days, we slowly drain the battery, take several days to build up the family of curves, but I end up with a curve like this:



        Notice I don't label anything with SOC, because it's not a useful number to me. I do my thinking, planning and worrying as volts per cell. I am planning to check this kind of curve every 6 months or so for curiosity. I'm curious as the bank ages and begins to degrade, does a) the slope in the flat area change, or b) the knees move towards the center, or c) both. Anybody else try this kind of plotting technique? I think it works because Grid-Zero limits by Amp draw from the battery, so long as my house load is large enough, I essentially am applying a constant draw (I usually use 7 A DC) as the programmed current limit. If I draw too slowly, I don't empty the bank before the sun comes up. If I draw too fast, I don't get much hourly data from OpticsRE. Now that I have Wattplot running, maybe I'll devise a test using 0.3C to speed it up.

        I know you've been monitoring your bank's health, thoughts on a, b or c; or other?

        In preparation for winter, I decided to use a cloudy/rainy weekend to disassemble and rebalance. In the Spring, I balanced at 2.900 volts/cell. I have had a cell that was running high since Oct 2nd. It wasn't the low and high cell I had been watching since the Spring. I had all those cell mini-BMS boards bolted to each cell, so, I don't know if they are part of the drift or not. Here's a photo from June during the build-up.


        Friday night, I took it apart to rebalance.



        This morning, I rebuilt the bank without anything strapped on top. Please, no licking the screens, you might get shocked.

        inMichigan

        Comment


        • #34
          Interesting setup. A few comments, and you know how much that's worth - ie <.02C.

          Like you, I like to be conservative, but have any of these cells *ever* been taken to full charge, ie 3.6v until .05C absorb is reached? We assume that the factory has done that, measured and discharged them before shipping, but do you really know?

          Personally, I like to do that to each new cell individually at least once, just to make sure that the electrolyte and other materials is spread out evenly inside, so as to reduce the possibility of hot-spot clumping later on. This also seemed to help get them in line faster, rather than walking around a bit for the first 10 cycles or so as the SEI layer grows to the normal depth.

          For me, that involves a 3.7v single-cell charger (bulk them first a bit to save time), or perhaps an adjustable bench power supply.

          After I've done that, then I go with more conservative charging values, like 3.5v per cell for normal cycling. Or now do your balance with whatever method you choose.

          Have you considered banding and strapping?

          Part of the reason for doing so, is that if one or more cells DO go rogue, or there is a mishap of some sort, without any banding the cases will swell instead of vent. Now you have cells hurting their neighbors, not to mention that the materials inside are no longer in good contact with each other - which leads to more swelling. They can also break your rack, or the cell-links bend and bind, causing case deformation and possible failure to formerly good cells.

          The way you are treating them seems to be conservative, and you may not encounter any issues. But there is always a manufacturing defect that might show up a year down the road, causing a cell to go rogue, and instead of just that one venting, it swells instead causing issues.

          I'm the last person to try and create drama where there isn't any, but I think banding and strapping is just good engineering. And for goodness sake, fabricate a COVER over those cell terminals. (heh, one reason I recommend GBS to newbies - they come with one).

          Comment


          • #35
            Nice system !! I wondered why you chose 2.90v as the balance point and still have boards that balance at 3.55 ?? It seems like that would give you a divergence in the voltage on upper end where you do most of the work.

            Comment


            • #36
              Originally posted by inMichigan View Post
              Between OpticsRE, Wattplot & Excel, I can graph every which way, any particular questions?
              Thanks for all the detailed information. Really liked your spreadsheet, good to see everything laid out like that. I am intrigued to know how you got the SOC versus voltage figures on the spreadsheet.

              I started out planning to use Mini-BMS with HomeBoard, contactor, etc... in fact, I bought the materials. I then decided to keep it simple--my choice. I decided the risk of the monitoring system (48->12V step down to feed the contactor) was adding more risk than I wanted, so, I decided to just trust the relay in the Radians to disconnect per it low voltage disconnect. Yes, I know that relays can fail. My thought is that to destroy the batteries, at a high level, I would need the relay to fail, the grid to go down, these two failures to happen after I've gone to sleep but not so close to sunrise that my battery bank can't sustain the house loads until the sun rises. I'm sure there are a few other rare but possible failures, in both the Outback side as well as any BMS side. So, bottom line, no automatic BMS for me. I write down setting changes in a log book. I do monitor the resting cell voltage with my Fluke.
              Yes it is always a balancing act, adding more complexity can add more things to fail. If you understand the weak points of the system and do the monitoring yourself I agree you don't need an automatic BMS. I don't have one either. Now for the system I put together for a friend, that is a different story.

              Did you mean "to destroy the batteries at a low level" rather than a high level, doesn't make sense to me otherwise.

              Notice I don't label anything with SOC, because it's not a useful number to me. I do my thinking, planning and worrying as volts per cell. I am planning to check this kind of curve every 6 months or so for curiosity. I'm curious as the bank ages and begins to degrade, does a) the slope in the flat area change, or b) the knees move towards the center, or c) both. Anybody else try this kind of plotting technique? I think it works because Grid-Zero limits by Amp draw from the battery, so long as my house load is large enough, I essentially am applying a constant draw (I usually use 7 A DC) as the programmed current limit. If I draw too slowly, I don't empty the bank before the sun comes up. If I draw too fast, I don't get much hourly data from OpticsRE. Now that I have Wattplot running, maybe I'll devise a test using 0.3C to speed it up.

              I know you've been monitoring your bank's health, thoughts on a, b or c; or other?
              Am I right in thinking that the way you usually run your battery is to fully charge it up assuming enough sunlight during each day and run it down each night at a maximum rate of 7 amps. I am interested to know what rate you charge the battery at and the average percentage of SOC that you cycle the battery each day.

              I agree with you about looking at cell voltage rather that SOC. I think that it is cell voltage and temperature that are probably the main factors that affect lifespan of the battery, not SOC.

              The plots are very interesting. It will certainly be useful to see how they change with time.

              I have decided not to do any special charge/discharge tests to see how my battery is going, mainly because it is my only source of power so is difficult to take offline to do the test under controlled conditions. I am going to compare data on a year by year basis to see how the battery performance changes with time under normal operating conditions. So far I haven't noticed any change in the battery performance.

              As the battery ages I would expect to see the knees move closer together as the battery looses capacity and the whole curve to drop down as the battery impedance(resistance) gets larger. I don't have a clue as to whether the battery impedance will change with SOC which will change the slope, will be interesting to see what happens.

              It is a shame you aren't plotting the individual cell voltages over time. I would expect them to diverge as the battery gets older if the cells loose capacity at different rates and their impedance vary relative to each other.

              In preparation for winter, I decided to use a cloudy/rainy weekend to disassemble and rebalance.
              I am interested in your experience with cell balancing over time. I and a number of others in Australia have found that the batteries do go out of balance over a time period of a year or so. I currently manually rebalancing my battery about every year or so.

              Simon
              Off-Grid LFP(LiFePO4) system since April 2013

              Comment


              • #37
                Originally posted by karrak View Post
                Am I right in thinking that the way you usually run your battery is to fully charge it up assuming enough sunlight during each day and run it down each night at a maximum rate of 7 amps. I am interested to know what rate you charge the battery at and the average percentage of SOC that you cycle the battery each day.
                Just a quick note before work, I'll answer the other questions later.

                I combined a lot of material into that post...so this point didn't come across correctly.

                My normal mode of operation is Radian's Grid-Tie. At night, the battery bank is not drawn down lower than my V_sell setting. If the power happens to go out at night, there would be no limit to the Amp pulled out of the bank, and it would run until the inverter's low battery cutoff kicks in (I hope). This is one of my big risks of such a small bank...pulling high current. I've trained my family to disconnect the hot water breaker if they notice during grid-down if the sun is not shinning. (I plan to automate this task with using an Insteon 240V controlled switch, I/O module and 5V wall plugged into a pure grid outlet.)

                When I want to play mad scientist, I switch into Grid-Zero mode. Then, the DoD_voltage and DoD_amps limits kick in. Grid-Zero is way to use up power stored in the batteries while still staying in sync with and connected to the grid should any 'large' load come up. So, when I set DoD_amps to 7, should the water heater come on, that extra power comes from the grid. I guess it's a way to simulate living off-grid, yet, have a safety net.

                In the latest Mate3 software, there is a way to automatically jump between modes based on time. I haven't given it a serious test yet. The use I have in mind is to change into Grid-Zero every night at 6 pm and back to Grid-Tie at 7 am. However, in this case, I would set the Grid-Zero voltage to be the same as V-sell (so it really would only kick in the grid went down while we are sleeping) and I would set the DoD_amp to something reasonable that would protect the batteries from heavy discharges (until the day I raise my bank size). I need to talk to Radian about this to make sure I know what will happen at night, grid-down, and a high load comes on exceeding the DoD_limit.

                inMichigan

                Comment


                • #38
                  Originally posted by karrak View Post
                  Thanks for all the detailed information. Really liked your spreadsheet, good to see everything laid out like that. I am intrigued to know how you got the SOC versus voltage figures on the spreadsheet.
                  I looked over several university papers on lithium batteries, as well as reading several forums. I wanted to convert V into % just to give me a visual aid when reading people's post that talk about %'s...
                  I chose to call 3.5V as 100% This seems to be commonly used.
                  I chose to call 2.6V as 0% This one is somewhat arbitrary, but I don't think anybody argues there is any usable stored power below 2.6V

                  The values at the bottom and top that are described as damaged and destroyed were my notes from reading what people thought happened at those places which I do not want to go.

                  Originally posted by karrak View Post
                  It is a shame you aren't plotting the individual cell voltages over time. I would expect them to diverge as the battery gets older if the cells loose capacity at different rates and their impedance vary relative to each other.
                  I think you mean this:


                  easier to see the 'difference' from the average


                  Rebalancing happened before the
                  "1st" new batteries arrived for bench testing
                  "4th" installed into cabinet and setup the full system on the 'wall'
                  "7th" rebalance and prepare for winter

                  Originally posted by karrak View Post
                  Did you mean "to destroy the batteries at a low level" rather than a high level, doesn't make sense to me otherwise.
                  Oh, poor choice of words on my part, correct, they would be destroyed at a low voltage, I meant high level as in "big picture" sort of way.

                  Comment


                  • #39
                    Originally posted by Willy T View Post
                    Nice system !! I wondered why you chose 2.90v as the balance point and still have boards that balance at 3.55 ?? It seems like that would give you a divergence in the voltage on upper end where you do most of the work.
                    I was after the ability for each cell to signal 'low voltage' to then trigger the contactor. The bleeder function at the high end should not have been engaged.
                    inMichigan

                    Comment


                    • #40
                      Originally posted by PNjunction View Post
                      Have you considered banding and strapping?
                      In the photo where they are lined up on a board, that was just to make it easy to connect all the terminals in a row for balancing. Do you mean to strap them together when they are in the white battery cabinet? What would be the benefit?
                      inMichigan

                      Comment


                      • #41
                        Originally posted by inMichigan View Post
                        I was after the ability for each cell to signal 'low voltage' to then trigger the contactor. The bleeder function at the high end should not have been engaged.
                        inMichigan
                        The boards have 3 functions, they will signal low and high voltage at cell level and the independent balance function. You do have to have one on each cell to give you cell level information to trigger the alarm / contactor. By using 2.90v bottom balance point it seems like you are pulling them out of balance with each charge / discharge cycle, it looks like from your data that imbalance magnifies itself over time.

                        My setup is the similar to yours, I balanced them at 3.50v initially in the parallel configuration, it took 3 days to equalize the pack . The daily charge voltage is 3.40v to 10% EA, so I have never reached the automatic balance function ( 3.55v ). After a year of cycling the cells are still balanced within .01 of each other. Yes, they would be out of balance on the low end, but thats why I have the boards and they are not out of balance on a daily basis within the voltage range I use. The low end of my discharge range is 3.10v.

                        I am not saying one scheme is right and one is wrong, just telling you how I do it. I also prepared spread sheets, but there wasn't really any data to record as long as they stay balanced. I am going to do a overall capacity test in the spring, thats about the only data I need. I'd expect 2-4% a year in capacity loss, anymore makes them unacceptable.

                        Comment


                        • #42
                          Originally posted by inMichigan View Post
                          I looked over several university papers on lithium batteries, as well as reading several forums. I wanted to convert V into % just to give me a visual aid when reading people's post that talk about %'s...
                          I chose to call 3.5V as 100% This seems to be commonly used.
                          I chose to call 2.6V as 0% This one is somewhat arbitrary, but I don't think anybody argues there is any usable stored power below 2.6V
                          None below 2.9. But you have one heck of a problem on your hands. On 10/24 somehow you were extremely unbalanced, and came very close to destroying some cells, all caused by your Vampire Boards. Lithium Batteries do not become unbalanced as they have no parasitic losses, but somehow you became extremely unbalanced all caused by the Vampire Boards themselves. You were just minutes away from destroying cells. The boards themselves cause the unbalance and destroy the cells.
                          MSEE, PE

                          Comment


                          • #43
                            Originally posted by Sunking View Post
                            None below 2.9. But you have one heck of a problem on your hands. On 10/24 somehow you were extremely unbalanced, and came very close to destroying some cells, all caused by your Vampire Boards. Lithium Batteries do not become unbalanced as they have no parasitic losses, but somehow you became extremely unbalanced all caused by the Vampire Boards themselves. You were just minutes away from destroying cells. The boards themselves cause the unbalance and destroy the cells.
                            Removed the boards this past weekend... If I run for months and do stay in balance, I would then conclude with my own data that vampire boards must not be installed on banks using a bottom balance strategy.

                            In hindsight, once I decided to not proceed with a contactor circuit setup for a low voltage disconnect system, I should have taken them off. I also regret not serializing each board with a number to match up against my batteries (tracked by serial number)....one of those boards is really not like the others.

                            inMichigan

                            Comment


                            • #44
                              Originally posted by Willy T View Post
                              The boards have 3 functions, they will signal low and high voltage at cell level and the independent balance function. You do have to have one on each cell to give you cell level information to trigger the alarm / contactor. By using 2.90v bottom balance point it seems like you are pulling them out of balance with each charge / discharge cycle, it looks like from your data that imbalance magnifies itself over time.
                              My charging strategy was attempting to always remain low enough to avoid the bleeder function kicking in. However, had I ever crept over that limit (or if the limit is not a on/off function), that is certainly a good way to explain my spread of voltages. Now that I've removed the boards, time will tell.

                              Can anyone comment if the bleeding function is a discrete switch or analogy by-pass filter behavior for Mini-BMS boards?

                              inMichigan

                              Comment


                              • #45
                                Originally posted by inMichigan View Post
                                Removed the boards this past weekend... If I run for months and do stay in balance, I would then conclude with my own data that vampire boards must not be installed on banks using a bottom balance strategy.
                                No you do not need Balance Boards if you BB. Myself and several other DIY EV folks DO NOT use BB or Cell Level Monitoring. In fact over 50% of DIY do not use any kind of external BMS other than what our controllers provide. Reason is real damn simple, we learned from experience and heartache of those that went before us or learned the hard way with our money. The Balance Boards are the root cause of failures. In effect you are paying for your own assassination. We Bottom Balance and quit worrying. With Solar even less need for any BMS other than what your Inveerter and charger provide. We just follow some simple rules even a 5th grader can do.

                                1. We take time when we receive the cells to Bottom Balance at 2.4 to 2.6 volts with all cells connected in parallel. The actual voltage is not important as long as the rested voltage falls no lower than 2.2 volts or higher than 2.6 volts. Lots of wiggle room to work with. What is important is all cells to be exactly the same voltage at the bottom with 0 AH capacity. At the bottom is the only place where the cells are all equal in voltage and capacity. There is no other point where the cells are equal. At the Top is the largest imbalance. At the Top only th evoltage is equal and nothing else, you have no idea what the capacity is. No cell at the Top will be equal capacity. Most of us use a [B]Revolectric Power Lab 8[/B] as it is a multi-tasker that can charge any battery of today and tomorrow with dead accurate precision.

                                2. Once Bottom Balanced the cells are then connected in series, and charged. While charging we monitor individual cell voltages. What we are looking for as the batteries charges is the cell with the HIGHEST VOLTAGE. That cell is the lowest capacity cell in the group. We charge until the weakest cell reaches 3.6 volts and terminate the charge. We then take note of the AH capacity that was pumped in. I did use 16S @ 100 AH CALB cells or a 48 volt 100 AH. On my system which is real typical the weakest cell was around 98 AH. The other 15 cells have the exact same 98 AH as the weakest cell. They just are not fully charged thus have a slightly lower voltage. My system is real typical the spread was small when rested. The weakest cell would settle at 3.45 volts, and thee Strongest around 3.39 volts. Voltage is not equal, but capacity is the same in all 16 cells.

                                3. We then run the cells no lower than 10 to 20% capacity and only charge to 80 to 90% capacity. Real easy to do and takes about a week to nail it. We set the voltagge of the charger to roughly 3.4 vpc. So on a 16S system 54.4 volts. We monitor the weakest cell resting voltage to be roughly 3.4 volts. All others will be slightly less. Only takes a few charge cycles to zero in on the final charger Set Point voltage. For me that is 53.8 volts. Average will be around 54 volts plus or minus .2 volts. On my system gives me roughly 90 AH capacity or 90% SOC. That takes care of the Charge side, and eliminates any possibility of an over charge. When you Top Balance you have to over charge all cells. That shortens cycle life.

                                4. On the Discharge Side we set our LVD to 3 vpc x Cell count. For me with a 16S system is 48 volts. Never have I ever had the LVD operate under normal conditions. Only during test runs I did to make sure it works. When it does operate all cells are at or extremely close to 3 volts. I even reset the LVD during a couple of test to 2.5 vpc or 40 volts. At 2.5 vpc all cells weree exactly 2.5 volts with 0 AH capacity making it impossible for any cell to be over discharged becausee no cell had any capacity lest to drive any adjacent cell into Reverse Polarity which is [B][U]Instant Death of a LFP cell[/U][/B]. With 48 volt LVD pack voltage it is impossible to ever over discharge any single cell. I have 8 volts of safety built in. The LVD will not allow the pack to go below 10% SOC. Very easy to implement on Solar and cost you NOTHING and you eliminate th eexpensive Vampire Boards which are the root cause of failures.

                                5. Lastly to BB one must be knowledgeable on Lithium batteries and make routine voltage checks on individual cells once a month or so. All you are looking for is before you charge, run the pack down and check individual cell voltages and make sure they are balanced at the BOTTOM. If not hook up your Power Lab 8 and Bottom Balance them again if ever needed. You do not have to disconnection any battery, you just do 8 cells at a time.

                                OK here is my direct experience and is repeated by the 34 other folks I network with have witnessed in EV's. I ran my 16S GBS 100 AH for 8 months. In that 8 months I lost roughly 5% capacity in all cells. I treat mine with TLC, more than anyone else, so they are not abused. After 8 months I decided to Bottom Balance again. It was a waste of time. There was less than 1% drift. Only degration was 5% capacity loss in 8 months which is normal with Chi-Com Cells. Instead of 90 AH usable capacity dropped to 84 usable AH. I use a Coulomb Counter as a Gas Gauge. Very accurate when used with Lithium cells. Most EV Controllers come with Coulomb Counters, and you can buy them fairly cheaply to use on solar. That gives me another added layer of protection. Any changes will become appearant very quickly, and I do not have to watch voltages. I just look at the gas gauge. I can see what I put in, and what I take out. In that 8 months only required one calibration.

                                Bottom Balance is not for everyone. You have to know WTF you are doing and understand the Lithium Technology. If you are a laymen, idiot, or a manufactured product like an EV or laptop, you must use Top Balance, spend the big bucks on a BMS and Vampire Boards, accept the fact it will shorten your cycle life, and risk destroying your expensive batteries. The most common failure mode of a BMS and Balance Boards is shorted. 16 cells = 16 eggs in the basket to break. What ever cell is attached to the BMS port, or the Vamp[ire Board is connected too, will be destroyed and not a damn thing you can do to stop it. You will not know it happened until after the fact. Not a big problem with a manufactured EV running 90S to 100S batteries. A faulted cell on a commercial EV can still get you to the shop if you have a few shorted cells. In that case the manufacture absorbs the cost. FWIW no commercial EV on the market will ever allow you to fully charge the battery without jumping through hoops. In the case of Tesla you must have Tesla approval and the code downloaded. If you run a 12 or 24 volt Solar System one single cell failure puts you in the dark. 48 volts and higher you can still limp along. Just do not push it because you are at high risk of a fire especially if you are not monitoring cell temps.

                                Oh FWIW I no longer use my Chi-Com LFP batteries. I got rid of them and sold them because I know 1 to 2 years is all I can get out of them. Me and a couple of friends bought teamed up and bought two late model Nissan Leaf Battery Modules. I now run 31S 60 AH on my EV. 1 friend used his to make his NEV 15S2P @ 120 AH, and the other uses 15S2P @ 120 AH on his Off-Grid shack in the Panama Jungle baby. The one in the Jungle is a Ex-Pat biker from the USA and grow Ganja and sells it to tourist here in Panama. He makes a fortune doing it. $200K/year is a lot of money in Panama. It cost us roughly $1000 each for 2014 and 2015 model year Leaf Batteries. All of us BB.

                                Good Luck to you.
                                MSEE, PE

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