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LifePO4 batteries for use with Midnite Classic 150?

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  • #61
    Originally posted by karrak View Post

    Big problem with this approach is that if the cells are balanced at the bottom end they will not be balanced at the top end unless their capacity is the same
    Do you understand what you just said? It was really ignorant. If you bottom balance, capacity is equal at all levels of SOC. BB is the only way you can equalize capacity. Top Balance and the cell capacity is never balanced, only voltage and only at 100% SOC. At 100% SOC the pack capacity is limited by the weakest cell in the pack. If Bottom Balanced it is dang near impossible to over discharge. Over Discharge can only happen if you Top Balance.
    Last edited by Sunking; 02-08-2016, 12:07 AM.
    MSEE, PE

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    • #62
      Originally posted by karrak View Post
      You could use something like that. If you connect up the individual 'balance' wires from each cell to the B6AC you can do the initial balance with the cells in series using the balance program.
      How old will he be when it balances the cells?

      is charger only has a 0.2 amps balance charge current for each amp hour out of balance requires 5 hours to correct. No BMS or hobby charger is capable of doing initial (aka gross) balance in any reasonable time frame. All BMS including hobby chargers can only perform maintenance Balance. New cell SOC level is broad of 30% range. On a 100 AH battery a difference of 30 AH is reasonable expectation of 40/70% SOC. With a 30 amp spread with 0.2 amps balance current is 30 AH / 0.2 amps = 150 hours or 6 days to balance. If using a solar source with a 4 Sun Hour day will take 36 days. His chargger like any BMS is for maintenance only. You will grow old waiting for them to do the initial or gross balance.

      Sorry Simon you are full of poop.Try reading the specs if you are capable. Page 22 of the manual. Please go ahead and read it. Balance Current 200 ma/cell.

      Pre Balance aka gross or initial is done by connecting all cells in Parallel, not series. Then you either Top or Bottom Balance.

      Createthis read this short white paper on Initial Balance, Karrak is giving you really bad advice. The White Paper backs up what I am telling you. If that does not convince you then read this White Paper on Gross Balance and look at the first chart, locate 200 ma on the Horizontal scale at mid point, then follow it up to 30 AH. Then look at the Vertical line for time and you will see 6 days. Make sure you read the conclusions especially the first one: "Balancing compensates for the SOC of individual cells. It does not compensate for capacity imbalance". The only way to balance capacity is via Bottom Balance. Do you need proof of that to?
      Last edited by Sunking; 02-08-2016, 12:27 AM.
      MSEE, PE

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      • #63
        Originally posted by Sunking View Post
        Do you understand what you just said? It was really ignorant. If you bottom balance, capacity is equal at all levels of SOC. BB is th eeonly way you can equalize capacity. Top Balance and the cell capacity is never balanced, only voltage and only at 100% SOC. At 100% SOC the pack capacity is limited by the weakest cell. If Bottom Balanced it is dang near impossible to over discharge. Over Discharge can only happen if you Top Balance.

        What he said wasn't ignorant. It was accurate.

        Top balance means capacities are off at the top and over charging is a risk. Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing.

        I feel like this thread is those two guys in Frozen arguing bark side up or bark side down.

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        • #64
          Originally posted by Sunking View Post
          How old will he be when it balances the cells?On a 100 AH battery a difference of 30 AH is reasonable expectation of 40/70% SOC.
          I don't see why the cells should be out by 30%. If they are all from the same manufacturing batch they will all have been charged to the same SOC so should only be out by a couple of % at most.

          If they are badly out of balance to start with you can charge them in series until they start balance charging then parallel them up and charge them at 6 amps

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

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          • #65
            Originally posted by karrak View Post
            I don't see why the cells should be out by 30%.
            That tells me you have never worked with Chi-Com batteries, or any lithium batteries for that matter. I know of no one, no company, or no standard that would even suggest wiring new batteries in series and use a balance charger to Balance them. That could take months depending on the size of the cells. That is just plain silly talk.

            I take that back, I do know someone who would recommend wiring new cells in series and use a Balance Charger to do Gross Balance. Only you Karrak would recommend that. You are on a lsland of your own making. Anyone who has ever worked with lithium cells knows the first thing you do is wire all the cells in parallel. Then either Bottom Balance or Top Balance. If this poor guys wires his cell in parallel will make a 400 AH pack. Assuming 50% SOC just how long does it take to charge them with 6 amps? 200 AH / 6 amps = 33 hours. Hell of a lot better waiting days for the Balance Chargers to Top Balance in series. While he is waiting he can paint a wall, and then watch paint dry to keep him entertained.
            Last edited by Sunking; 02-08-2016, 12:54 AM.
            MSEE, PE

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            • #66
              I will say the one thing bottom balancing seems to have going for it (other than being cheaper), is that you aren't charging the cells to full capacity, which they don't like anyway.

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              • #67
                I ordered a GBS battery, because it was easy to order and the shipping was simple/free. I ordered a Cell-Log8s and an LVD, but not the balance modules. If I decide I need them, they're only $45 for a 4 pack. I'm looking forward to this. Should be fun.

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                • #68
                  Balancing lifepo4 is simple matter and if you have the right equipment it's effortless. All this babble about top and bottom balancing is ridiculous and really shows how little some know about how to use the technology properly. It also seems those in USA are years behind us, as they still don't have dedicated lifepo4 charge controllers, we've had them for years. Now we are about to launch a new one within the next 3 months, they are 60amp, charge each cell line individually and cut of charge when each cell line reaches it's upper parameter. So no need to balance.

                  Presently we use bulk charge lifepo4 charge controllers, which bulk charge the pack to 14v then switch off and restart charging at 13.6v. They disconnect load at 12v, so never over charger or discharge. We also use individual cell monitors for our customers, which connect a discharge circuit when one cell goes over 3.5v and that will discharge the cell at the rate of charge.

                  We balance our cells at 3.2v before installing and that's it. So far and with hundreds of system in place over the last 5 years, none have any pack problems, just a few wiring or board components failing and they are all within the first 3 months. Our longest commercial installation is now close to 5 years old, still provides 100% of its energy and all the other are the same. We make sure our systems are idiot proof and don't require user input, which says a lot of problems.

                  However there can be charging a balance differences in how you use lifepo4 packs. if you are using lifepo4 for hobby or EV, then you may have balance and charge problems, because most times you are charging when the pack is not in use. But if you have an off grid or mobile system, then it is constantly in a state of discharge and this tends to keep the pack reasonably balanced.

                  In my own home system, I have just have bulk chargers connected, each charge has 750w of panels. The chargers are connected in parallel to 500ah pack connected in parallel, we have found this setup works best. Too big a pack and yo have problems, plus in an off grid situation you need power always, so if one pack system has problems, you can isolate it from the other packs and still have energy, unlike a big pack which would need to be shut down to fix.
                  Last edited by dax; 02-08-2016, 05:48 PM.

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                  • #69
                    I had a 48 volt 100 AH set of them. I liked them mechanically, but performance lacked due to very high internal resistance of the cells and higher than expected capacity loss. Mechanically I liked the covers and 4-point bussbars. But for the 23% higher price than CALB's was very disappointing performance. So got rid of them and replaced them with Leaf cells.

                    When you get them use the busbarrs and connect them in Parallel and walk away for a day. That will mid Balance them which does not mean much except make them safe to either Top or Bottom Balance. If you use your hobby charger and decide to Top Balance, it is going to be a very slow process and you will not be able to detect when they are fully charged with a 6-amp charger with all 4 cells in parallel. At 400 AH you hold 3.6 volts until charge current Tapers to 3% of C. 3% of C on a 400 AH battery is 12 amps. See the problem? Only way to Top Balance with your Hobby Charger is one cell at a time and terminate when charge current tapers down to 3 amps. Either way will take a couple of days with 4 cells. See a problem with that?

                    Never heard of a RC hobby charger limited to 50 watts, especially if you are running RC heli's. Those guys use large 6S 6000 mah packs and larger. A 50 watt charger would take 3 hours to charge a 6S@6000 mah pack. Ever consider getting a Cellpro Power Lab 8? It would make short work of maintaining and Gross Balance your new cells with either top or bottom balance @ 60 amps charge or discharge current.
                    MSEE, PE

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                    • #70
                      Originally posted by dax View Post
                      Balancing lifepo4 is simple matter and if you have the right equipment it's effortless. All this babble about top and bottom balancing is ridiculous and really shows how little some know about how to use the technology properly.
                      You have to perform a Initial aka Gross balance when you receive them, and either pick Top or Bottom. No way around it no matter what country you are from. After that just stay away from the knees using CC/CV, no BMS required.
                      Last edited by Sunking; 02-08-2016, 06:10 PM.
                      MSEE, PE

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                      • #71
                        Originally posted by createthis View Post


                        What he said wasn't ignorant. It was accurate.

                        Top balance means capacities are off at the top and over charging is a risk. Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing.

                        I feel like this thread is those two guys in Frozen arguing bark side up or bark side down.


                        You and SK are going back and forth on this one because you are using the same words with different meanings. The quote above can be made accurate by simply substituting SOC for capacity.

                        If capacity means how many AH can be withdrawn from a cell starting at its current state and going to a stopping point which is determined on a per cell basis, then SK is correct that in a bottom balanced bank all cells will always be at equal capacity. But at no point but the bottom will they be at the same SOC, measured on a per cell basis.

                        If by capacity you mean the total AH capacity of a cell, not a bank, as determined on a per cell basis, then no amount of balancing will produce a bank with equal cell capacities. Capacity defined that way cannot be changed except by partially destroying the better cells. Using this definition of the word, balancing does not equalize capacity, it equalizes SOC (Post #62). The point at which the SOCs match must be specified (either top or bottom) since cells of different individual capacity cannot stay balanced through charge or discharge if you pass the same current through all of them.

                        And then there is a hint of a third definition of capacity being used by createthis, which has something to do with how much farther you can charge a given cell before reaching 100% SOC./

                        Seems simple enough, but easy to provoke disagreement and talking past one another when you do not share the same definitions of the words you use.
                        If you actually read your posts and SK's posts you may realize that you are both describing the same physical reality even though you seem to be disagreeing.
                        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                        • #72
                          Originally posted by inetdog View Post



                          You and SK are going back and forth on this one because you are using the same words with different meanings. The quote above can be made accurate by simply substituting SOC for capacity.

                          If capacity means how many AH can be withdrawn from a cell starting at its current state and going to a stopping point which is determined on a per cell basis, then SK is correct that in a bottom balanced bank all cells will always be at equal capacity. But at no point but the bottom will they be at the same SOC, measured on a per cell basis.

                          If by capacity you mean the total AH capacity of a cell, not a bank, as determined on a per cell basis, then no amount of balancing will produce a bank with equal cell capacities. Capacity defined that way cannot be changed except by partially destroying the better cells. Using this definition of the word, balancing does not equalize capacity, it equalizes SOC (Post #62). The point at which the SOCs match must be specified (either top or bottom) since cells of different individual capacity cannot stay balanced through charge or discharge if you pass the same current through all of them.
                          Correct sir.

                          In Bottom Balanced system at 2.5 volts, all cells will have the exact same capacity of 0 AH per cell, and all SOC voltages of 2.5 volts per cell. Both Capacity and SOC are equal at the Bottom in a Bottom Balanced System. Thus you have no need to monitor cell voltages to protect over discharge. Setting the Inverter to 10.5 volts or greater does that for you.

                          In a Top Balanced system all cells are charged to 100% SOC and capacity AH is not equal and unknown. Only SOC is known, not AH capacity .No two cells are equal in AH capacity and Chi-Com cells AH capacity tolerance is sloppy -3%/+15%. So a 4S pack weak cell can be as low as 97 AH, and the highest of 115 AH. The 4S pack capacity is dictated by the weakest cell in the string just like links in a chain. In this example is 97 AH would be maximum AH capacity. The 115 Ah cells can eat the 97 AH cell if discharged down to the PACK 20%SOC voltage of 12 volts. In a Top Balanced system you must have cell monitors with a LVC circuit to operate if any cell reaches 2.5 volts which wil be the weak 97 AH cell. The other three cells stil have capacity left in them to drive the discharge cell to reverse polarity. Game over.

                          Having said that BB systems should only be attempted by experienced users who fully understand the technology. All commercial systems use Top Balance for liability reasons and added profit.
                          Last edited by Sunking; 02-08-2016, 08:52 PM.
                          MSEE, PE

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                          • #73
                            Originally posted by createthis View Post
                            What he said wasn't ignorant. It was accurate.
                            No sir it is not

                            Originally posted by createthis View Post
                            Top balance means capacities are off at the top and over charging is a risk.
                            That part is half correct, At the top, all cells are at maximum capacity, but capacity is not equal. The only thing that is equal at the top is SOC voltage of 3.6 volts. Both over charge and over discharge are is highly likely without a BMS.

                            Originally posted by createthis View Post
                            Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing.
                            None of this statement is correct and leading you to the wrong conclusions. When you BB all cells both AH capacity and SOC voltages are equal in all cells. Capacity = 0 AH, and SOC Voltage = 2.5 volts. Over discharge risk is minimized to almost impossible. Like Top Balance, over charge is possible with BB system if you try to push the weak cell to high. The magic of BB systems is capacity is equal in all cells at all SOC levels. You stop charging when the weak cell reaches 80 to 90% SOC. So in the proceeding example if the weak cell is 97 AH and you charge the weak cell to 90% capacity, all cells have 87.3 AH. The weak cell will have ever so slightly higher voltage than all others when charged up. But the voltage difference is very small roughly .05 volts or less. The weak cell should be up around 3.41 to 3.43 volts at rest, and the others around 3.36 3.38 volts so in a 4S pack totals roughly 13.5 volts.
                            MSEE, PE

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                            • #74
                              Originally posted by Sunking View Post
                              PN I think you would agree the CALB's are the best of the Chi-Coms. Would you not agree with that?
                              In our application, which is a realtively low-current energy-storage application, and not a "power" application like an EV, I think the differences are minimal. EV's - certainly I'd use the higher-end calb's.

                              That being said The CALB's are less expensive and twice the warranty/cycle life of GBS and Winston. Knowing that which one would you buy?
                              That's great if one can get that deal. Not that you'll get any great performance advantage in our low-current application, but sure no problem with Calb.

                              Today i have Leaf cells in the cart operating at 96ish volts. Mucho Better performance. Very low voltage sag when accelerating, and very little capacity loss for their age. Me and a couple of friends down here bought a set of Leaf Batteries from a salvage yard.
                              Some EV guys are going that route. Different chemistry, different charge / maintenance procedures.

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                              • #75
                                Originally posted by inetdog View Post
                                1. If you build a battery bank out of random off the dealer's shelf cells, all the same brand and model and hopefully same or similar manufacturing date, how likely is it that the cells will be reasonably (within the capacity of the BMS to handle) balanced as to SOC when you get them?
                                They usually arrive sitting around 3.2v, but that means nothing really from a capacity standpoint. You could purchase four 100ah cells, but lo and behold, they mistakenly slip in a 60ah cell. Yet all four are sitting at 3.2v upon arrival.

                                Instead of buying random, you deal with a distributor that will ship cells ideally from a sequential set. Some contain bar-codes or other identifiers. Upon request, some even come with test sheets showing both capacity and IR all along the charge/discharge curve - if you want to go that far. Most pre-made packs, or batteries from reputable dealers aren't just cobbled together from a random shelf-pull, unless one is going cheap.

                                2. Same question but a group of cells ordered new from the factory or from a large internet dealer as a single order? Better or worse than the first situation?
                                New from the factory usually means China - and sometimes that poses problems for some. US or other country distributors may have stock in your continent/country/state.

                                GBS can be found in many places, but the main distributor in the US is Elitepowersolutions.

                                CALB in the US is mainly in Pomona, Ca. CALB USA Inc.

                                Some EV places carry all the major brands, like Evolve Electrics, EV Source, EV West etc. Others may find LFP at batteryspace, or GWL/Power in Europe. So you can deal direct with the mainland, with a trusted nearby main distributor, EV outlets, and even battery specialist places like batteryspace. Find one you can trust.

                                3. Same question but this time you buy a preassembled battery pack with an integrated BMS?
                                Sure! Many do. Remember that most of the time the main customer is EV users, who may put together higher-voltage / multiple bank systems, rather than us simplistic guys putting together simple 4S / 8S / 12S systems for an energy-storage application.

                                Where between those two extremes do the boards continue to make sense? Clearly not for typical solar PV where charge/float time is limited, and especially if you deliberately never bring the bank to 100% SOC where the cell bypass function kicks in.
                                Vampire boards are too risky, and prone to failure causing the problem they are meant to cure! In addition, they have their own accuracy specs, which can deviate over time, so you really ARENT balanced at all. Just making voltmeters line up. Meanwhile ....

                                The point being that we have a tendency to overcomplicate the issue with endless top/bottom balancing talk. Most users just go underground now with shared experiences as the topic is an endless rehash over and over.

                                Charge each cell individually to 3.6V, falling to .05C. If you haven't purchased hacker trash, you'll be close in both capacity and internal resistance. Close is good enough in our application. You'll never need to charge to this level again. This is an initial charge.

                                Normal charging - 3.4 to 3.45v per cell. Absorb current can fall to almost nothing at 3.4 without harm as you'll never fully charge it and leave it that way without use at some point.

                                Stop when any cell gets to 2.7v under load. This is fine in our application. Stop sooner if you like. Heck, even your typical 10.7 to 11.2v lead-acid lvd will stop you from destroying the bank completely, although at that point, I'd recharge *slowly* to get back to at least 3.1v and then don't do that again on a regular basis.

                                My suggestion is to just get a sample small 4S bank, and test it. Then you'll see where you can ignore about 2/3rds of all forum talk based on your own desires and experience.

                                Make it simple or complex - it's up to you.
                                Last edited by PNjunction; 02-09-2016, 04:37 AM.

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