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LiFeP04 Batteries for Solar & BMS

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  • #46
    Originally posted by Living Large View Post
    I need my memory refreshed Dereck. With the Xantrex equipment and programmable low and high voltages, the purpose of this BMS would only be to detect faults where I want to shut down?
    Correct the BMS is there only for the batteries. Having said that the BMS can send signals to control whatever you want. Example the Orion Jr, if used with a EV can tell the motor controller to go into Limp Home mode meaning reduce motor current. There are several outputs you can program to do whatever you want. What I cannot answer because I have no experience with them is the Xantrex Inverter. If it has control inputs I would guess they are logic level and should work. Sounds like a Home Work assignment for you.
    MSEE, PE

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    • #47
      Originally posted by Sunking View Post
      Correct the BMS is there only for the batteries. Having said that the BMS can send signals to control whatever you want. Example the Orion Jr, if used with a EV can tell the motor controller to go into Limp Home mode meaning reduce motor current. There are several outputs you can program to do whatever you want. What I cannot answer because I have no experience with them is the Xantrex Inverter. If it has control inputs I would guess they are logic level and should work. Sounds like a Home Work assignment for you.
      Yeah, but the XW does not appear to be designed to work with any inputs other than the single REMOTE POWER OFF. Now that I understand BMSs a lot better, and returning to the conversation we were having 1 to 1-1/2 months ago, I better appreciate the thinking that solar equipment is not ready for LFP. But this may be all I need.

      If the initial balancing is done, the batteries are monitored regularly to assess health (which the Orion does), and the BMS will prevent a meltdown by enabling me to create a POWER OFF signal, that appears to cover all the bases, unless I missed something.

      It is described two ways in the Schneider documentation. Connect a switch between this pin and ground, normally open. Also, as a logic level input. Either way, this should do the trick.

      EDIT I spoke with a Schneider rep via email today. He said there currently is no ability for BMS input (which we know), and that a third party disconnect would be needed. Schneider feels the built in functionality at the pack level should cover most situations. The rep did say that they are considering adding such additional capabilities, and that a firmware update is possible. I suppose that alludes to the XW possibly issuing a command for the MPPT to shut down if it receives a Remote Power Off, because currently I don't believe there are any inputs on the MPPT other than battery temp. What I could do is create a circuit that drives that battery temperature input, and shorts it to create what the MPPT sees as a fault condition, according to the manual. Might be able to just parallel a relay across the temperature sensor, driven by the BMS circuit.

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      • #48
        I have 780ah lifepo4 fed by 2000w of solar running a house (plus 250w wind generator), in the 8 months it has been operating never got to LVD, so top balance and use a dedicated BMS with active cells balancers and relay driven charge and LVD cut off.

        Yet to find a solar charge controller that does the job for lifepo4. We have 24v cells and 12v storage, just about everything runs through a 3000-6000w PSW inverter and seems to run flawlessly. My LVD is 3v and top, 3.6v.

        Also have 480ah lifepo4 and 100w solar running a 100w inverter and 204v and 12v appliances in a motorhome. I have yet to reach LVD in either our motorhome or house and in the MH, use the lifepo4 for hot water and A/C sometimes. This lifepo4 pack has been in use for more than 18 months and functions flawlessly. I have a small 2.3v charger for bringing up any cells that don't make the grade at the top, but only used that once when I installed them and since have changed the connection for input and output, so now every thing works fine.

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        • #49
          Originally posted by tasman View Post
          I have 780ah lifepo4 fed by 2000w of solar running a house (plus 250w wind generator), in the 8 months it has been operating never got to LVD, so top balance and use a dedicated BMS with active cells balancers and relay driven charge and LVD cut off.

          Yet to find a solar charge controller that does the job for lifepo4. We have 24v cells and 12v storage, just about everything runs through a 3000-6000w PSW inverter and seems to run flawlessly. My LVD is 3v and top, 3.6v.

          Also have 480ah lifepo4 and 100w solar running a 100w inverter and 204v and 12v appliances in a motorhome. I have yet to reach LVD in either our motorhome or house and in the MH, use the lifepo4 for hot water and A/C sometimes. This lifepo4 pack has been in use for more than 18 months and functions flawlessly. I have a small 2.3v charger for bringing up any cells that don't make the grade at the top, but only used that once when I installed them and since have changed the connection for input and output, so now every thing works fine.
          Good to hear your LFP bank is stable - that is what seems to be the prevailing wisdom - if balanced initially.

          What do you mean by "yet to find a charge controller that does the job"? Can you not get the thresholds you want, the profile (CC, CV)? I haven't looked specifically yet at what the one I am considering offers, but was hoping I could program something acceptable. It is two of the Schneider 60A units.

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          • #50
            Originally posted by Living Large View Post
            Good to hear your LFP bank is stable - that is what seems to be the prevailing wisdom - if balanced initially.

            What do you mean by "yet to find a charge controller that does the job"? Can you not get the thresholds you want, the profile (CC, CV)? I haven't looked specifically yet at what the one I am considering offers, but was hoping I could program something acceptable. It is two of the Schneider 60A units.
            G'day, noticed some typing errors in my last post, our MH has 1000w of solar panels and 1000w psw inverter. If your charge controller is programmable and able to leave out the absorbion, float and temp compensation sections, then it will be fine if the upper and lower parameters you want can be set.

            My BMS sends a 12v signal to a 150amp relay when the cell pack reaches 14.4v and that disconnects the charger controller from the pack. The same when it reaches 12v, the bms sends a signal to another relay which switches of power. Haven't got to that stage yet of disconnecting power, but have reached the upper limits a few times when we have been away and the cell pack is only being used for fridge, freezer and security systems. When at home, we connect the MH to the house system which gives us more power to use.

            A lifepo4 solar charger should be one which can be programmed to suit lifepo4 battery pack requirements without temp, float and absorb sections. To me the best solar charger set up would be one which provides 150amp input and charges each cell line individually to a set parameter, then switches of each cell line when it reaches that number. Do the same with lower voltage paramaters and you have a charger controller that is also a bms. Not much different to current charger controllers which are all orientated to lead acid. This way there would be no need for cell balancers or to worry about anything, but enjoying your power supply.

            Sadly there doesn't seem to be any 3.2v cell chargers that have high amperage inputs, no good trying to charge 700ah with 4x4.5 amp chargers coming from a 60-120 amp supply.

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            • #51
              Originally posted by tasman View Post
              G'day, noticed some typing errors in my last post, our MH has 1000w of solar panels and 1000w psw inverter. If your charge controller is programmable and able to leave out the absorbion, float and temp compensation sections, then it will be fine if the upper and lower parameters you want can be set.

              My BMS sends a 12v signal to a 150amp relay when the cell pack reaches 14.4v and that disconnects the charger controller from the pack. The same when it reaches 12v, the bms sends a signal to another relay which switches of power. Haven't got to that stage yet of disconnecting power, but have reached the upper limits a few times when we have been away and the cell pack is only being used for fridge, freezer and security systems. When at home, we connect the MH to the house system which gives us more power to use.

              A lifepo4 solar charger should be one which can be programmed to suit lifepo4 battery pack requirements without temp, float and absorb sections. To me the best solar charger set up would be one which provides 150amp input and charges each cell line individually to a set parameter, then switches of each cell line when it reaches that number. Do the same with lower voltage paramaters and you have a charger controller that is also a bms. Not much different to current charger controllers which are all orientated to lead acid. This way there would be no need for cell balancers or to worry about anything, but enjoying your power supply.

              Sadly there doesn't seem to be any 3.2v cell chargers that have high amperage inputs, no good trying to charge 700ah with 4x4.5 amp chargers coming from a 60-120 amp supply.
              Thanks for the explanation. I believe the equipment I am considering is more compatible than yours, but that is a guess at this point. I won't be surprised if one or more issues arises when I look closer.

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              • #52
                LL FWIW I know you are not looking at Midnite Solar Classic Controllers but any of the Classic controllers have an Auxiliary Input (Aux 2) that allows an external signal to shut the charge off. Perfect for using a BMS. Check the product you are looking at and see if they have something similar.

                You just cannot use a relay to disconnect a CC as they need battery power applied at all times. Failure to do that can damage the controllers. However you can disconnect the solar panel with no problem All you gotta do is either open the circuit, or short them out.

                As for whatever controller you use, you are just going to use the Bulk portion which is Constant Current set to a higher voltage than needed. 58.4 volts should work just fine. When your first cell hits 3.45 volts, you terminate charge. That will put the weakest cell at approx 95% SOC and the rest slightly lower.

                Classic Manual
                MSEE, PE

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                • #53
                  Originally posted by Sunking View Post
                  LL FWIW I know you are not looking at Midnite Solar Classic Controllers but any of the Classic controllers have an Auxiliary Input (Aux 2) that allows an external signal to shut the charge off. Perfect for using a BMS. Check the product you are looking at and see if they have something similar.

                  As for whatever controller you use, you are just going to use the Bulk portion which is Constant Current set to a higher voltage than needed. 58.4 volts should work just fine. When your first cell hits 3.45 volts, you terminate charge. That will put the weakest cell at approx 95% SOC and the rest slightly lower.

                  Classic Manual
                  Thank you for this suggestion. At this point in time, considering the current desired functionality, it would be very wise to revisit the MS. FWIW, I did look at it a bit in the beginning, before I fell for the XW, and started leaning towards the Xantrex CC. The only synergy I was anticipating looking at Xantrex for both was sharing of settings, and having faith the MPPT and inverter/charger would be on the same page to an extent. This was largely as a noobie - thinking there would be an advantage to using the same manufacturer. If the MS has settable thresholds like the Xantrex, and the modes can be programmed as desired for LFP, then giddy-up!

                  Originally posted by Sunking View Post
                  You just cannot use a relay to disconnect a CC as they need battery power applied at all times. Failure to do that can damage the controllers. However you can disconnect the solar panel with no problem All you gotta do is either open the circuit, or short them out.
                  I was wondering about exactly where and how relays can be used, and what happens if a circuit is broken. I appreciate this information. I assume somewhere in the installation or user manuals this is covered. With an Aux input to shut down the XW, and an Aux input to shut down the MS MPPT, it is starting to almost sound like Nirvana. One thing I need to verify is the Remote Power Off of the XW shuts down both the inverter and charger - to account for both LVD and HVD faults.

                  I'll take another look at the MS. Thanks again.

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                  • #54
                    LL if the XW controller has an input to stop charging you are good to go. I cannot help you with that, well I could if I was not lazy tonight, so that is a Home Work assignment for you. Should be in the documentation or a quick e-mail to Xantrex. I just know it can be done with any MS Classic and Wizbang Jr.

                    As for most controller, in fact all that I know of there is a correct order for connection Battery first, then panels. To disconnect panels first, then battery.
                    MSEE, PE

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                    • #55
                      Originally posted by Sunking View Post
                      LL if the XW controller has an input to stop charging you are good to go. I cannot help you with that, well I could if I was not lazy tonight, so that is a Home Work assignment for you. Should be in the documentation or a quick e-mail to Xantrex. I just know it can be done with any MS Classic and Wizbang Jr.

                      As for most controller, in fact all that I know of there is a correct order for connection Battery first, then panels. To disconnect panels first, then battery.
                      Yes, that is my homework - I didn't expect you to do it. The manual says "shuts down the system". So it is left to the reader to determine if "system" means both the charger and inverter. Common sense would be it is both. I'll write Schneider and ask them, because it didn't occur to me to ask today.

                      Yep, disconnect panels first, then battery is very clear.

                      Comment


                      • #56
                        Originally posted by tasman View Post
                        Sadly there doesn't seem to be any 3.2v cell chargers that have high amperage inputs, no good trying to charge 700ah with 4x4.5 amp chargers coming from a 60-120 amp supply.
                        Tas - here is one CC/CV that might do with some warnings about usage. Admittedly a bit expensive if you are only doing 4 cells but it kind of proves my point:

                        http://www.batteryspace.com/Smart-Ch...tery-Pack.aspx

                        Note that this 40A / 3.2 (3.65v hvd) single cell charger is really intended for cells no larger than 400ah. See the capacity column for this 3.2v model:

                        http://www.batteryspace.com/smartcha...terypacks.aspx

                        So why is it limited to no larger than 400ah cells? Because at this rate of about 0.1C, it will reach 3.65v with minimal electrolyte heating.

                        BUT, you *could* use it, provided you watched it like a hawk, and when it stalls between 3.45 and 3.5v, (or better yet just starts to drop below 40a) you pull it (essentially you are *starting* out at .05C, which is typically considered the current you stop charging with). You DON'T allow the charger to finish and shut off by itself. If you used this on a 700ah cell, eventually it would try to go to zero amps and stall, but NEVER reach 3.65v and merely heat the electrolyte because you are just under the wire at .05C. EVENTUALLY, yes it will reach 3.65v, but that is due to electrolyte heating, (applied high voltage but no current flowing) and not from charging. Hence the common recommendation not to go lower than 0.1C, unless you know up front that you should set your hvd low.

                        At 700ah, I don't know how long or how much degradation from electrolyte heating would cause, but I can see it happen pretty rapidly on my 40ah cells.

                        For your 12v application, the same consideration is given to solar. It is quite feasable that you could be at 95% SOC on your first sunny day, but the next - bad weather arrives and you are charging with <0.1C. If your high cutoff voltage is set too high, then the bank slowly finishes charge at a lower voltage, and spends the rest of the day heating the electrolyte *trying* to get to say 3.6v. And it will, but that is due to parasitic reactions.

                        That's why my moral with solar is to set your hvd low to no more than 3.5v since we can't control the environment. In some cases with low current, the only time the bleedoff circuits would activate is when the cells are actually finished charging, and are now rising in voltage due to electrolyte heating! No balancing is taking place at low currents.

                        You've got a lot more to lose with 700ah than I do with 40ah. However, because I run conservatively, and started out sanely, I run bare with NO balance boards whatsoever because in a "Sub C" application, the cells tend to stay in the condition of balance they were first left in. Running >1C regularly, or abusing them with higher or lower voltages than necessary can change that. If you stay within a window of sanity, I can get away with going bare.

                        This allows me to use off the shelf chargers and controllers that operate on the pack-level (two terminal), as long as temp comp is defeated, the HVD is no more than 14.1v (common "gel" setting if I can't set it lower myself), and a float at 13.6v (3.4v per cell), is benign as it is well under the higher-voltage that can cause electrolyte heating when used in a relatively low current application.

                        Anyway, that's my take on being conscious of differentiating between EV / RC applications, and relatively low-current solar.

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                        • #57
                          Originally posted by Sunking View Post

                          You just cannot use a relay to disconnect a CC as they need battery power applied at all times. Failure to do that can damage the controllers. However you can disconnect the solar panel with no problem All you gotta do is either open the circuit, or short them out.
                          The relays I use, switches to another contact which disconnects the battery pack, when this happens it connects to a 12v supply that takes over from the upper paramater signal and supplies power to the relay constanly, to keep the charge disconnected. To switch on charge, I have a switch which turns of the power to the relay and charge returns. I have a led light which tells me without checking the bms that charge is off, then I chek the bms to see the pack charge state and switch of the relay supplying power to the main relay keep charge dosconnected and it charges.

                          It works well when I tested it, but haven't need it because the packs stays within the top and bottom voltage parameters all the time. Because there is always a frdge and freezer going even when no one is home.

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                          • #58
                            Originally posted by tasman View Post
                            ....My BMS sends a 12v signal to a 150amp relay when the cell pack reaches 14.4v and that disconnects the charger controller from the pack.....
                            Ouch. You want to disconnect the SOLAR PANELS from the charge controller. The controller wants to be powered by the battery bank all the time.
                            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                            solar: http://tinyurl.com/LMR-Solar
                            gen: http://tinyurl.com/LMR-Lister

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                            • #59
                              Originally posted by Mike90250 View Post
                              Ouch. You want to disconnect the SOLAR PANELS from the charge controller. The controller wants to be powered by the battery bank all the time.
                              Sorry getting my way of putting things wrong again, assumed eveyone would know you disconnect the panles from the controller, just like at night as it requires full battey connection to function. Just like a BMS. The LVD works after the charger as well, have no idea how it will work if it every reaches the top or bottom paramaters. Only tested it when it was put together, been in use since and never need to work.

                              Put my systems together with no knowedge to start with and no access to any help being as remote as we are and until a while ago, no real communications other than constant drop out mobiles. So just begining to learn and discuss, seems haven't yet learnt how to phrase things properly so most understand.

                              Got my MH pack out now changing a few thing around from what Iv'e picked up here and researched, which has given me answes to some questions and knowledge to solve some myself. So hang in with me for awhile whilst I get the gist of how this forum works best and fit in with it. When I post something, it's really learning how others see my systems and addng that to better my knowledge and approach. Some times may post something I haven't really thought deeply enough about so gives the wrong impression, so it's good it gets noticed and corrected.

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                              • #60
                                How much is average for 1ah of the LiFeP04 these day? Where you buy them from?

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