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  • #31
    Originally posted by Sunking View Post

    Tell me more about the Vampire Boards. What functions do they perform? Is it bleeding only? Or do they also measure the voltage and temp also? I suspect they do it all if I remember correctly. Been a while since I looked. Don't worry to much about them because essentially if your charger never goes above 13.8 volts, they should never trigger the bleeders. And if you ask me nicely I can tell you how to disable them. They have a power resistor to burn the power off when turned on. Cut one end of it and open it up. Think of it like a washed out bridge.
    Thanks for the info on the GBS vs CALB, I will consider this further.

    Here are the specs on the Elite BMS:
    Main Screen Display: Pack Voltage, Pack Current, Battery Capacity, Alarm Message
    Individual Cell Screen: Cell number, voltage and temperature
    Computer Input Power: 9-20V, 120mA
    Battery Voltage: 12-500V
    Shunt Input: 500A = 50mV
    Pack Voltage Resolution: 0.2V
    Current Resolution: 0.1A
    Temperature Measurement Range: -99F to +199F or -146 to +92C
    Video Output: Composite Video, Color, NTSC, RS-170
    Measurement accuracy: Better than 1% of Full Scale
    Maximum number of cells supported: 140
    Balancing Threshold: 3.55V
    Balancing Current: 0.5A
    Alarm Output Current: 4A surge for 100mS, 2A continuous*
    Optional Data Interface: CAN
    Ground Fault Detection: 2mA (5000 Ohm/Volt)

    I am pretty sold on the concept of bottom balancing and monitoring for voltage drift (easy to do when it's all spelled-out for you on the LCD screen), but I doubt the bleeder boards will be doing any cell balancing with the conservative charger settings we are using.

    When it comes down to it I will basically be using the BMS as my battery monitor (cell voltages, temp, overall voltage and amps in/out) and more importantly as a source for a backup LVC/HVC if my chargers/inverter do not shut down on their own. The cost for all of that is $345 (plus the LVC/HVC contactors, which I would buy anyway), and I will NOT have to buy the Victron BMV702 as my energy monitor (which costs $205), so the difference in cost between no-BMS + BMV702 and the full-system just described is only $140. If I went with no BMS I would have to figure out a way to have that secondary LVC/HVC control.

    Comment


    • #32
      Originally posted by ASprinter View Post
      I am pretty sold on the concept of bottom balancing and monitoring for voltage drift (easy to do when it's all spelled-out for you on the LCD screen), but I doubt the bleeder boards will be doing any cell balancing with the conservative charger settings we are using.

      When it comes down to it I will basically be using the BMS as my battery monitor (cell voltages, temp, overall voltage and amps in/out) and more importantly as a source for a backup LVC/HVC if my chargers/inverter do not shut down on their own. The cost for all of that is $345 (plus the LVC/HVC contactors, which I would buy anyway), and I will NOT have to buy the Victron BMV702 as my energy monitor (which costs $205), so the difference in cost between no-BMS + BMV702 and the full-system just described is only $140. If I went with no BMS I would have to figure out a way to have that secondary LVC/HVC control.
      I think you have a decent MOP going for you. The real challenge for you is when you receive the cells how you will implement the initial Balance Act being it Top, Middle or Bottom.

      Here is a little tib bit if you have not already discovered it. When you Bottom Balance you are making a known reference point of 0 AH or 0% SOC. The cell voltages will only be equal at the Bottom. But here is the catch. On the first couple of charges you need to watch the cell voltages. You are looking for the weakest cell, or the cell with the lowest AH Capacity. That cell wil be the one with the highest voltage when they approach being fully charged. That cell will be full before the others. So you need to watch and note when it gets to roughly 3.5 volts. From 3.5 to 3.6 volts is a fast ride and happens quickly.

      So I have a suggestion and I do not know if your Elite System can do this or not. I know the Orion can. You want it to send a signal to the charger to either Turn off, or lower the voltage to Float when the first cell reaches 3.55 volts. At the cell with your low charge rate wil be roughly 95% SOC and that is all she's got Scotty. That is when you want to terminate. After a few times via trial and error you can find the right Absorb voltage.

      Good luck, keep doing homework, and I will be happy to answer questions. If I do not know the answer, I know where to find them.
      MSEE, PE

      Comment


      • #33
        Originally posted by Sunking View Post
        I think you have a decent MOP going for you. The real challenge for you is when you receive the cells how you will implement the initial Balance Act being it Top, Middle or Bottom.
        I have decided on bottom balance approach. I looked into the CellPro Multi4 and it does not have discharge capability. I'm guessing there are others available if not using a light bulb or something to draw power. That's research for another day, but at a glance the $89 iCharger 106B+ may do I what I need for less than half the cost of the CellPro 8.

        So I have a suggestion and I do not know if your Elite System can do this or not. I know the Orion can. You want it to send a signal to the charger to either Turn off, or lower the voltage to Float when the first cell reaches 3.55 volts. At the cell with your low charge rate wil be roughly 95% SOC and that is all she's got Scotty. That is when you want to terminate. After a few times via trial and error you can find the right Absorb voltage.
        With the Elite, you cannot adjust the voltage at which the boards start shunting, it is set at 3.55V. Additionally, over-voltage triggers when the highest cell voltage hits 3.8V (gulp) and undervoltage triggers when the lowest cell hits 2.8V. That would be unacceptable to me except that I plan for the solar cc and shorepower charger to stop charging well before that, so 3.8V would only be achieved if all hell broke loose and my chargers somehow did not automatically stop charging. There is a CANBUS option on the Elite BMS but I have no idea how it would interact with the programmable Magnum inverter/charger. Maybe this would be a good time to talk about what the Orion Jr has to offer. The BMS comparison website you sent me indicating that the Orion Jr also uses shunt-based passive cell balancing, only there are no vampire boards attached to each cell as the Jr does it internally. Does this make it any better than the Elite? How complex is the setup on a Jr and what are some of the advantages? I can't seem to find much information on it, and particularly not for use in a boat or RV.

        Good luck, keep doing homework, and I will be happy to answer questions. If I do not know the answer, I know where to find them.
        You've provided me a lot of great information, so thanks again!
        Last edited by ASprinter; 03-16-2017, 06:50 PM.

        Comment


        • #34
          Originally posted by ASprinter View Post
          I have decided on bottom balance approach. I looked into the CellPro Multi4 and it does not have discharge capability. I'm guessing there are others available if not using a light bulb or something to draw power. That's research for another day, but at a glance the $89 iCharger 106B+ may do I what I need for less than half the cost of the CellPro 8.
          I owned an Icharger 106B+ some time ago. Good little charger but I think I should point out some things you may not be aware of. Here is the one big limitation. Max discharge current is 7 amps or 20 watts, whichever comes first. What that means is If the charger has to dissipate more than 20 watts, you wil not get the full 7 amps without a Ballast resistor. Example say a 20 volt battery would limit you to just 1 amp. 20 volts x 1 amp = 20 watts. You woul dhave to use a 350 watt resistor to take the heat off the Icharger to get 7 amps. Now at 3.2 volts of LFP is no problem at 7 amps.

          Now here is the kicker when you get your cells and parallel them up you will have a 3.2 volt 800 AH Battery. Lets say they arrive at 60% SOC that means they have 480 amp hours you need to bleed off. See the problem? It would take you 480 AH / 7 amps = 68.5 hours to discharge them, almost 3 days.

          The PL8 is not much better at 10 amps 100 watt imit. So what is a guy to do then?

          Well cheer up there are a couple of ways. I won't leave you down and out for the count.

          1. Connect the batteries in series to make your 12 volt battery. Make you a plug if you want to use say the Icharger to monitor cell voltages, or use a DMM. Go down to Wally World and buy some cheap Car Head Lights. Most are around 50 to 70 watts, so you would want a few of them. Current = Power / Voltage. So at 200 watts / 12 volts = 16.6 amps. You can go up to 1000 watts if you can afford it.

          2. This is how I would do it because it is cheap. You do just like above but use Power Resistors. So here is how you do it. For each 100 watt resistor is roughly 1.5 Ohms a common resistor value. at 12 volts, a 1.5 ohm resistor will draw 8 amps. So say you buy 5 100 watt power resistors and wire them in parallel. You just made a 40 amp discharger. Once you get the voltage bleed down, you can them start removing resistor to lower the drain for more control. Careful though we are talking some HEAT, an dif you leave at the wrong time and let ig to far you could do damage. But you have a extra set of eyes. Use your Elite and LVD to shut it down.

          Sound good?




          Originally posted by ASprinter View Post
          With the Elite, you cannot adjust the voltage at which the boards start shunting, it is set at 3.55V. Additionally, over-voltage triggers when the highest cell voltage hits 3.8V (gulp) and undervoltage triggers when the lowest cell hits 2.8V. That would be unacceptable to me except that I plan for the solar cc and shorepower charger to stop charging well before that, so 3.8V would only be achieved if all hell broke loose and my chargers somehow did not automatically stop charging.
          No problem assuming your batteries are in good health and you only charge to 13.8 volts you should not trigger, but it is possible. Example for whatever reason a cell fails, deteriorates, or become really unbalanced it is possible for a cell to go over 3.6 volts. Example 3 cells charging at 3.3 volts an done faulty cell at 3.6 volts = 13.5 volts with a charger set at 13.8 volts. It is possible, but that is what you have a monitor and eyes for.

          Originally posted by ASprinter View Post
          There is a CANBUS option on the Elite BMS but I have no idea how it would interact with the programmable Magnum inverter/charger. Maybe this would be a good time to talk about what the Orion Jr has to offer. The BMS comparison website you sent me indicating that the Orion Jr also uses shunt-based passive cell balancing, only there are no vampire boards attached to each cell as the Jr does it internally. Does this make it any better than the Elite?
          First that is the difference between a Distributive BMS (Elite), and a Centralised BMS (Orion) Get it? Secondly it is the quality of the parts. Elite is Chi-Com and I do not know what chip set if any they use. Orion uses a TI Chip set you can program and good ole USA made. OK for plus an minuses a Centralised BMS requires 2-wires for every cell. Not a big deal on a 4S system, a cable management problem on a 100S system. Distributive requires a Vampire Board on every cell and a loop signal cable to Control Unit. Understand?

          Originally posted by ASprinter View Post
          How complex is the setup on a Jr and what are some of the advantages? I can't seem to find much information on it, and particularly not for use in a boat or RV.
          You've provided me a lot of great information, so thanks again!
          Easy to program. The Orion is tailored to a low voltage EV of 8 to 16S. You get a coulomb counter, CANBUSS to work with a Motor Controller. The advantage is like you noted you can program Trigger points. Or if it sees a problem with any cell it can react and do something, whatever you want it to do. In an EV if it sees a cell go low, it can reduce power or Limp Home Mode, or operate the LVD to save the battery. It has Diagnostics, data logging, bells and whistles. More than what you probable need and unless you are a code bug the Elite will probably work OK for you. The Orion just does a lot more and flexible.
          MSEE, PE

          Comment


          • #35
            Originally posted by Sunking View Post

            2. This is how I would do it because it is cheap. You do just like above but use Power Resistors. So here is how you do it. For each 100 watt resistor is roughly 1.5 Ohms a common resistor value. at 12 volts, a 1.5 ohm resistor will draw 8 amps. So say you buy 5 100 watt power resistors and wire them in parallel. You just made a 40 amp discharger. Once you get the voltage bleed down, you can them start removing resistor to lower the drain for more control. Careful though we are talking some HEAT, an dif you leave at the wrong time and let ig to far you could do damage. But you have a extra set of eyes. Use your Elite and LVD to shut it down.
            Sounds like an excellent solution to me! For something I'm probably only going to use once a year (or less), it's easier to stomach the $89 investment for the iCharger than the $275 for the CellPro 8.


            First that is the difference between a Distributive BMS (Elite), and a Centralised BMS (Orion) Get it? Secondly it is the quality of the parts. Elite is Chi-Com and I do not know what chip set if any they use. Orion uses a TI Chip set you can program and good ole USA made. OK for plus an minuses a Centralised BMS requires 2-wires for every cell. Not a big deal on a 4S system, a cable management problem on a 100S system. Distributive requires a Vampire Board on every cell and a loop signal cable to Control Unit. Understand?

            Easy to program. The Orion is tailored to a low voltage EV of 8 to 16S. You get a coulomb counter, CANBUSS to work with a Motor Controller. The advantage is like you noted you can program Trigger points. Or if it sees a problem with any cell it can react and do something, whatever you want it to do. In an EV if it sees a cell go low, it can reduce power or Limp Home Mode, or operate the LVD to save the battery. It has Diagnostics, data logging, bells and whistles. More than what you probable need and unless you are a code bug the Elite will probably work OK for you. The Orion just does a lot more and flexible.
            It seems to me like the Elite is a good compromise for my application...no programming required, everything is set up to work in an RV setting as I plan to use it. Perhaps later in life when I have more time to play with BMS's I'll give something like the Orion a try.

            Thanks again for all the help! I will be starting to buy parts soon and will report back.

            Comment


            • #36
              Originally posted by ASprinter View Post
              Thanks again for all the help! I will be starting to buy parts soon and will report back.
              You are welcome. Just make damn sure you have the time available when you go to bottom balance, like a free day. Start in the morning after your shower and breakfast. One thing about LFP batteries is the charge/discharge curve is very FLAT. For the most part 3.3 to 3.0 volts will go SLOWWWWWWWWWWWW and as exciting as watching grass grow. But once you hit 3.0 volts things go real fast and you are minutes away to 2.5 volts. Once you see the voltage drop and pass 3.0 volts, stop, and remove a couple of resistors to slow things down. By the end only 1 resistor so you can control what is going on. I will say this again, the resistors are going to be HOT, so make sure you have protection when handling. Remember when you were a kid and touched a light bulb? That kind of HOT. Stay on top of it and do not let it get away from you. Below 2 volts and you will damage them. Stop at 2.5 volts.

              Good luck, and keep us posted.
              Last edited by Sunking; 03-21-2017, 11:15 AM.
              MSEE, PE

              Comment


              • #37
                SK--I am reading back through this thread making sure I understand everything you've written. One concept is still a little fuzzy to me...

                Originally posted by Sunking View Post
                1. Set Bulk/Absorb to 13.8 volts, and FLOAT to 13.6 volts. Set Absorb time to 30 minutes initially. This method is going to require you to observe charge current for a week or so. What is going on is your Controller will stay into Constant Current phase until the battery voltage reaches about 13.8 volts, then at that point is Constant Voltage or Absorb stage begins. The charge current will start to taper off as the batteries Saturate to 13.8 volts. Ideally you would want to Terminate Absorb when the current tapers to 5% of C. Example if the cells are rated 100 AH, then 5 amps. Well your Solar Charger does not do that, it uses time. So what you have to play with it to find that amount of time it takes until you see the current taper down to around 5%. Don't sweat bullets trying to nail 5%, just do not let it go to 0 amps which would be 100% charged, you want to avoid that. Using this method gets to to mid/high 90's% SOC which is pushing your luck a bit. Once the timer times out the voltage switches to a lower FLOAT voltage of 13.6 volts and your batteries FLOAT while your panels supply power to loads until sunset.

                2. Is my favorite because it is the no fuss or worry method. Just set Bulk/Absorb to 13.8 volts, ZERO minutes Absorb, and Float to 13.6 volts. Works exactly like above, except as soon as the Controller detects the charge current starts to Taper Off will lower the voltage to 13.6 volts and the batteries will Float. Like above the panels will provide power to the loads until sunset.

                The difference between the two options is option 1 gets to to mid/high 90% SOC and option 2 gets you to high 80, low 90's% SOC.
                I am having difficulty understanding how scenario 1 and 2 would produce different results. I am using a single 300W solar panel with a short circuit current of only 9.7 amps and a 200AH battery, which means current will always be less than 5% of C, essentially meaning that under scenario 1 my absorb time would be 0. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

                Comment


                • #38
                  Originally posted by ASprinter View Post
                  SK--I am reading back through this thread making sure I understand everything you've written. One concept is still a little fuzzy to me...



                  I am having difficulty understanding how scenario 1 and 2 would produce different results. I am using a single 300W solar panel with a short circuit current of only 9.7 amps and a 200AH battery, which means current will always be less than 5% of C, essentially meaning that under scenario 1 my absorb time would be 0. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?
                  OK you are quite a bit lite on panel power for such a large battery. If this was a 12 volt 200 AH battery would require a minimum 300 watt panel to generate a C/10 Charge Current. Lithium can run quite a bit higher wattage. Typically you would want C/4 on a lithium or 50 amps, and that would take 650 watts.

                  However you are missing an important characteristic of controllers. With a PWM controller INPUT CURRENT = OUTPUT CURRENT. So if you had a PWM Controller your output current would be around 8 amps and at 12 volts is 100 watts from a 300 watt panel.

                  Now RELAX because with a MPPT Controller OUTPUT CURRENT = PANEL WATTAGE / BATTERY VOLTAGE. So do the math. 300 Watts / 12 Volts = 25 amps and on a 12 volt battery is 300 watts from a 300 watt panel.

                  Do you feel better now? So if your controller is rated at least 25 amps, you are OK. FWIW you can calculate the maximum controller wattage input from the current rating and battery voltage.

                  Watts = Amps x Battery Voltage. Example an 80 amp Controller with a

                  12 volt battery = 1000 watts
                  24 volt battery = 2000 watts
                  48 volt battery = 4000 watts.

                  So here is something to think about if you have not bought anything yet. You are going to have 8 cells configured 4S2P for 12 volts @ 200 AH. Consider 8S1P of 24 volts @ 100 AH. Gives you a lot more room to grow with on your Controller. Twice as much to be exact. Does not change battery capacity.

                  Battery Capacity Watt Hours = Volts x Amp Hours.

                  12 volts x 200 AH = 2400 Watt Hours
                  24 volts x 100 AH = 2400 Watt Hours

                  Configured for 24 volts, the charge current drops to 300 watts / 24 volts = 12.5 Amps. Still the exact same charge rate of C8 either way.
                  Last edited by Sunking; 03-21-2017, 08:49 PM.
                  MSEE, PE

                  Comment


                  • #39
                    Originally posted by Sunking View Post
                    OK you are quite a bit lite on panel power for such a large battery. If this was a 12 volt 200 AH battery would require a minimum 300 watt panel to generate a C/10 Charge Current. Lithium can run quite a bit higher wattage. Typically you would want C/4 on a lithium or 50 amps, and that would take 650 watts.
                    I'm actually doing better than most with a 300W panel and 200ah of battery. I would say 200W of solar and 200 ah of AGM batteries is pretty typical among Sprinter van owners, but the 300W LG Neon 2 panel is the same size as the 200w panel it replaced thanks to technology improvements. I will also have the advantage of the lithium battery's lower internal resistance, particularly above 85% SOC. There simply isn't any more room on the roof for more.

                    Now RELAX because with a MPPT Controller OUTPUT CURRENT = PANEL WATTAGE / BATTERY VOLTAGE. So do the math. 300 Watts / 12 Volts = 25 amps and on a 12 volt battery is 300 watts from a 300 watt panel.
                    You're right, I was doing the calc incorrectly.

                    So here is something to think about if you have not bought anything yet. You are going to have 8 cells configured 4S2P for 12 volts @ 200 AH. Consider 8S1P of 24 volts @ 100 AH. Gives you a lot more room to grow with on your Controller. Twice as much to be exact. Does not change battery capacity.
                    The 3rd generation 200ah GBS battery is a 4S config.....4 cells at 3.2V each.

                    I am still hung up on my original question though...post 37 above, and how the scenarios would produce a different result.

                    Comment


                    • #40
                      25 A is greater than 5% of C, right? If you manage to hit absorb in the middle of the day, you would have enough charge current available to see the tapering current at 13.8 V that indicates you are getting a higher SOC.

                      (Your​ peak sustained charge current is more likely to be 20 A with this panel, but even that might be enough to get some good from absorb if the timing works out)
                      Last edited by sensij; 03-22-2017, 02:15 AM.
                      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                      Comment


                      • #41
                        Originally posted by ASprinter View Post
                        I'm actually doing better than most with a 300W panel and 200ah of battery. I would say 200W of solar and 200 ah of AGM batteries is pretty typical
                        Yes that is typical for a lead acid battery. They cannot charge as fast as Lithium batteries. What might be part of your confusion is Pb batteries are sized for 5 day Reserve Capacity so you only discharge 20% per day. That gives you 2.5 days usable to stay above 50% on Pb. Pb batteries are charged at C/12 to C/8 with C/10 being perfect

                        Lithium is a different animal and you size them for 3 days with 2.5 days usable. It would take a 12 volt 335 AH AGM to equal a 12 volt 200 AH LFP. Both batteries require the same panel wattage of 450 to 500 Watts. The AGM charges at C/10 and the LFP would charge at C/6. LFP is good to C/2 or 100 amps in your case.

                        Originally posted by ASprinter View Post
                        The 3rd generation 200ah GBS battery is a 4S config.....4 cells at 3.2V each.
                        OK my bad, I thought they were 100 AH, so you can only have 12 volts @ 200 AH

                        Originally posted by ASprinter View Post
                        I am still hung up on my original question though...post 37 above, and how the scenarios would produce a different result.
                        Like you said, you did the Calcs wrong. 300 watts into a 12 volt battery generates 25 amps, and 25 amps on 200 AH battery is C/8. Again this has to do with you being a little light on panel wattage. 5% of 200 AH is 10 amps aka C/20. 25 amps is greater than 10 amps aka C/8. For GBS I think they specify C/33 or 3% or 6 amps on a 200 AH battery.

                        Do not get to hung up on all that. You are not charging to 14.4 volts when the charge current cut-off really matters. You are only going to 13.6 to 13.8. Your current taper to 0 and life is good. You wil just Float and use Solar Power until dark.

                        MSEE, PE

                        Comment


                        • #42
                          I got that part, it's this part I'm confused about:

                          Originally posted by Sunking View Post
                          1. Set Bulk/Absorb to 13.8 volts, and FLOAT to 13.6 volts. Set Absorb time to 30 minutes initially. This method is going to require you to observe charge current for a week or so. What is going on is your Controller will stay into Constant Current phase until the battery voltage reaches about 13.8 volts, then at that point is Constant Voltage or Absorb stage begins. The charge current will start to taper off as the batteries Saturate to 13.8 volts. Ideally you would want to Terminate Absorb when the current tapers to 5% of C. Example if the cells are rated 100 AH, then 5 amps. Well your Solar Charger does not do that, it uses time. So what you have to play with it to find that amount of time it takes until you see the current taper down to around 5%. Don't sweat bullets trying to nail 5%, just do not let it go to 0 amps which would be 100% charged, you want to avoid that. Using this method gets to to mid/high 90's% SOC which is pushing your luck a bit. Once the timer times out the voltage switches to a lower FLOAT voltage of 13.6 volts and your batteries FLOAT while your panels supply power to loads until sunset.

                          2. Is my favorite because it is the no fuss or worry method. Just set Bulk/Absorb to 13.8 volts, ZERO minutes Absorb, and Float to 13.6 volts. Works exactly like above, except as soon as the Controller detects the charge current starts to Taper Off will lower the voltage to 13.6 volts and the batteries will Float. Like above the panels will provide power to the loads until sunset.

                          The difference between the two options is option 1 gets to to mid/high 90% SOC and option 2 gets you to high 80, low 90's% SOC.
                          I am having difficulty understanding how scenario 1 and 2 would produce different results. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

                          Comment


                          • #43
                            Originally posted by ASprinter View Post
                            I am having difficulty understanding how scenario 1 and 2 would produce different results. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?
                            Are you suggesting that because they are both floating at the same voltage, they must have the same SOC? If that were true, why would you bulk charge to 13.8 V at all? The path you take to float voltage matters because you are dealing with chemical reactions, and not instant transfers of energy. In scenario 1, as long as you have enough sun to drive current you get more productive time at 13.8 V (with the current falling as the reactions that can occur at that voltage taper off), which drives the SOC higher. In scenario 2, you only touch 13.8 before dropping down to 13.6, so those extra energy storage reactions don't occur and your SOC is slightly lower.
                            Last edited by sensij; 03-23-2017, 12:33 PM.
                            CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                            Comment


                            • #44
                              Originally posted by sensij View Post

                              Are you suggesting that because they are both floating at the same voltage, they must have the same SOC? If that were true, why would you bulk charge to 13.8 V at all? The path you take to float voltage matters because you are dealing with chemical reactions, and not instant transfers of energy. In scenario 1, as long as you have enough sun to drive current you get more productive time at 13.8 V (with the current falling as the reactions that can occur at that voltage taper off), which drives the SOC higher. In scenario 2, you only touch 13.8 before dropping down to 13.6, so those extra energy storage reactions don't occur and your SOC is slightly lower.
                              When charging terminates I recognize that the voltage will settle at a lower point, but I thought the 13.6V float charge was to essentially keep the batteries at a specified level and also to do the heavy lifting when loads are applied, rather than pull down the battery SOC. For another point of comparison, what would your SOC look like if you bulk charged to 13.8V and did not do a float at all?

                              Comment


                              • #45
                                Originally posted by ASprinter View Post
                                what would your SOC look like if you bulk charged to 13.8V and did not do a float at all?
                                A LFP fully charged rested battery is 3.45 volts or 13.8 volts on 4S. So it means it is possible if you set the charger to 13.8 volts, you can reach 100% SOC. That happens when charge current reaches 0-Amps and the battery is then fully saturated.

                                Example if for some reason you did not use much the night before, come sunrise you start charging and say by 10 in the morning you reach 13.8 volts, by afternoon your battery will reach 100%. Something tells me this will happen quite a bit in an RV that is not being used everyday.
                                Last edited by Sunking; 03-23-2017, 05:49 PM.
                                MSEE, PE

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