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  • #61
    Originally posted by ASprinter View Post
    That is something I never thought about; particularly since GBS packages these cells, stores and ships them on their side. How critical is this, as it would be very difficult for me to mount this in any position other than on its side.
    Oops, I have got it wrong, upright or on the side is OK, on the back is bad. See here for more information http://visforvoltage.org/forum/9972-...ll-orientation

    Very interesting chart, thank you for posting that. I wonder how similar my GBS cells would be compared to the Winstons. If you look at the chart I posted, 3.35vpc would be about 28% SOC at 0.5C while a .05C charge on your chart could be 65% SOC. Goes to show why you can't rely on voltage with LiFePO4 cells, which makes it a little more nerve wracking for newbies like me.
    Yes the rate of charge makes a big difference! Another issue when charging with solar is that the charge current can vary from the maximum the solar panels can put out under full sun to nearly zero during heavy cloud cover or in the early evening which can make a difference to the final %SOC that your battery ends up at.

    These are the only settings I can adjust in my solar charge controller. Do you see any problems with these settings?
    They look fine to me. Having the float voltage at 13.2V (3.3V/cell) will mean that your battery will not be kept at ~95%-98% full while the sun is up. You say you have been looking at the Cruising forum and they say not to keep the battery at a high SOC for extended periods. I agree with this if the battery is not being used or used infrequently, under these circumstances the battery SOC should be kept around 40%-50%. On the other hand if the battery is in use all the time as with my system and other off grid systems with things like fridges switching on and off I don't think this is such an issue. Let me know if you want a technical description of why this is so.

    The charger was only matching the 0.8 amps being pulled by the BMS, contractors & LCD screen, according to the shunt-based reading and I confirmed with a clamp meter.
    Looking through the MMS1012 manual it looks like the default float voltage is 13.4 (3.35V/cell) which is too low to charge an LFP battery, however if you have the ME-ARC Inverter Remote you can custom program the MMS1012.

    Simon

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

    Off-Grid LFP(LiFePO4) system since April 2013

    Comment


    • #62
      Originally posted by karrak View Post
      Oops, I have got it wrong, upright or on the side is OK, on the back is bad. See here for more information http://visforvoltage.org/forum/9972-...ll-orientation
      It's something I never would have thought about, so thank you. Glad this side orientation works because it's my only choice!


      Yes the rate of charge makes a big difference! Another issue when charging with solar is that the charge current can vary from the maximum the solar panels can put out under full sun to nearly zero during heavy cloud cover or in the early evening which can make a difference to the final %SOC that your battery ends up at.
      I was babysitting the batteries for their first full charge today. My BMS needs at least one cell to hit 3.55v (to activate a balance board) for the SOC meter to work. (Only need to do once.) Just as everyone says, one minute the cells were in the mid-to-high 3.4s and within a couple of minutes they were at 3.55 and one hit 3.6 in the next 10 seconds before I could disconnect the solar. I was shocked how quickly that happened, especially since it sat the 3.3s for hours.

      Under no load my volt meter, the BMS and the solar charge controller all report around the same voltage, but when charging at 27.6V & 16.3A the solar charge controller was reading 0.2 volts higher than the battery voltage. I had to temporarily reprogram the charge controller for 14.4v (even though I wanted a battery voltage of 14.2v) so I could hit my 3.55vpc target. What is the best way to manage this since the charge controller's voltage reading will be higher than the real battery SOC at high charge rates, yet close to reality at lower charge rates?


      They look fine to me. Having the float voltage at 13.2V (3.3V/cell) will mean that your battery will not be kept at ~95%-98% full while the sun is up. You say you have been looking at the Cruising forum and they say not to keep the battery at a high SOC for extended periods. I agree with this if the battery is not being used or used infrequently, under these circumstances the battery SOC should be kept around 40%-50%. On the other hand if the battery is in use all the time as with my system and other off grid systems with things like fridges switching on and off I don't think this is such an issue. Let me know if you want a technical description of why this is so.
      Right now the battery is sitting at 13.36 v (no load) or 3.345 vac and the BMS is reporting that's about a 92% charge. That seems about right, which might make a good target float voltage. I can see now that 13.2 v would be much lower SOC. Probably too low for my needs.

      Looking through the MMS1012 manual it looks like the default float voltage is 13.4 (3.35V/cell) which is too low to charge an LFP battery, however if you have the ME-ARC Inverter Remote you can custom program the MMS1012.
      I do have the ME-RC50 remote that allows reprogramming of the bulk, absorb, float voltages but it sounds like that 13.0V is not adjustable. The troubleshooting section of the manual says "Charger says "Float Charging" not "Bulk Charging" when the AC is first plugged in: Check the DC Volts meter, if the battery is over 13.0 VDC then the battery was already charged, and the charger automatically goes to Float Charging to keep from overcharging the batteries."

      I hope there is a way to get around that...

      Comment


      • #63
        Originally posted by ASprinter View Post
        I was babysitting the batteries for their first full charge today. My BMS needs at least one cell to hit 3.55v (to activate a balance board) for the SOC meter to work. (Only need to do once.) Just as everyone says, one minute the cells were in the mid-to-high 3.4s and within a couple of minutes they were at 3.55 and one hit 3.6 in the next 10 seconds before I could disconnect the solar. I was shocked how quickly that happened, especially since it sat the 3.3s for hours.
        A couple of questions
        1. Did you balance the cells before the first charge and if so how did you do it?
        2. What is the make and model of your BMS?


        3.6V will not do any harm to any cell in the battery unless you left it sitting at 3.6V for a long period of time. You have to get to around 4.4V-4.5V before you start doing damage instantly. Your BMS should have disconnected the battery from the power source long before this happens.

        Under no load my volt meter, the BMS and the solar charge controller all report around the same voltage, but when charging at 27.6V & 16.3A the solar charge controller was reading 0.2 volts higher than the battery voltage. I had to temporarily reprogram the charge controller for 14.4v (even though I wanted a battery voltage of 14.2v) so I could hit my 3.55vpc target. What is the best way to manage this since the charge controller's voltage reading will be higher than the real battery SOC at high charge rates, yet close to reality at lower charge rates?
        Are "27.6V & 16.3A" a typo?

        You could reduce the both the positive and negative power cable length and/or increase the cable size. From your photo it looks to me like the black battery minus wire from the battery to the shunt is smaller than the other red power wires?

        You could set the controller at 14.2V with a long absorb time (say 60 minutes) so that the charge current will taper off and the battery voltage will slowly approach the 14.2V that you want. For normal use at 13.8V an absorb time of around 15 minutes would surfice.

        I do have the ME-RC50 remote that allows reprogramming of the bulk, absorb, float voltages but it sounds like that 13.0V is not adjustable. The troubleshooting section of the manual says "Charger says "Float Charging" not "Bulk Charging" when the AC is first plugged in: Check the DC Volts meter, if the battery is over 13.0 VDC then the battery was already charged, and the charger automatically goes to Float Charging to keep from overcharging the batteries."
        My understanding of float charging is that the power supply will supply whatever current is necessary to keep the battery at the float voltage. I think that if the Magnum supply sees a battery voltage of more than 13V when it is first connected that it will not try to take the battery to the bulk voltage (14.4V?) and skip the absorb phase of the charge. Instead it will provide enough current to charge the battery up to the float voltage of 13.4V. If I am right, if you change the float voltage to 13.8V the Magnum will provide maximum charge current until the battery voltage reaches 13.8V. I did see some settings that imply that you can limit the time that the Magnum will stay in float before shutting down altogether which maybe of use.

        Simon

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

        Comment


        • #64
          Originally posted by karrak View Post
          A couple of questions
          1. Did you balance the cells before the first charge and if so how did you do it?
          2. What is the make and model of your BMS?
          The company I purchased from had balanced the cells but I was keeping a close eye on individual cell voltages while charging. All cells stayed within 0.03 volts of each other. My battery and BMS are made by Elite Power Solutions, also known as GBS batteries.

          3.6V will not do any harm to any cell in the battery unless you left it sitting at 3.6V for a long period of time. You have to get to around 4.4V-4.5V before you start doing damage instantly. Your BMS should have disconnected the battery from the power source long before this happens.
          The nominal specs are : Average 3.2 V (working) 3.65V-3.8V (peak ) 2.5 V ( cut-off low). The batteries spent several hours in the 3.3xV range and was only in the 3.4s for a short period of time and moving from 3.49-3.55 literally happened in a minute or two. As soon as the red light on one balance board came on at 3.55v indicating that cell's resistor was active, the capacity display that had been missing from the LCD monitor came alive. Literally within the 8 seconds or so it took me to throw a blanket over the solar panel it soared from 3.55 to 3.61V. I was shocked, but it didn't spend any more than a few seconds there, but the 3.8v cutoff was probably only a minute or two away at that point. After reaching that first initial full charge I put a load on the battery to bring the SOC down.

          Are "27.6V & 16.3A" a typo?
          That's what the Victron solar charge controller software said, but I'm not sure how that could be. It stated 249 watts, 27.6 v and 16.3 amps, which equals 449 watts. My panel is only a 300w.

          The screenshot was taken right as the first balance board light came on at 3.55v and the "real" battery voltage was 14.2v at that point. The charge controller was reading 14.4v but it was not that high.


          You could reduce the both the positive and negative power cable length and/or increase the cable size. From your photo it looks to me like the black battery minus wire from the battery to the shunt is smaller than the other red power wires?
          This is just a test rig, so yes, wires are very much undersized compared to the AWG 2 I will be using.

          You could set the controller at 14.2V with a long absorb time (say 60 minutes) so that the charge current will taper off and the battery voltage will slowly approach the 14.2V that you want. For normal use at 13.8V an absorb time of around 15 minutes would suffice.
          Sounds like a good approach. I'll start low, 13.8v and 10 mins of float and see where I end up.

          My understanding of float charging is that the power supply will supply whatever current is necessary to keep the battery at the float voltage. I think that if the Magnum supply sees a battery voltage of more than 13V when it is first connected that it will not try to take the battery to the bulk voltage (14.4V?) and skip the absorb phase of the charge. Instead it will provide enough current to charge the battery up to the float voltage of 13.4V. If I am right, if you change the float voltage to 13.8V the Magnum will provide maximum charge current until the battery voltage reaches 13.8V. I did see some settings that imply that you can limit the time that the Magnum will stay in float before shutting down altogether which maybe of use.
          That's what I thought too but the amperage coming from the inverter/charger is only matching the draw from the battery at the time; no charging. There is apparently a cc/cv mode that I have yet to find, so I am interested in researching that.


          Comment


          • #65
            Originally posted by ASprinter View Post
            There is apparently a cc/cv mode that I have yet to find, so I am interested in researching that.
            You are letting terms confuse you.

            Bulk/Absorb = CC/CV Mode
            Float = CC/CV Mode.

            Your charger is nothing more or less than a CC/CV mode charger. The only thing that changes is voltage set points. All you want to do is find the float voltage to get your batteries to 80 to 90% SOC and get rid of the BMS, Assuming you are operating at 12 volts is going to be roughly 13.6 volts. To turn your controller into pure CC/CV is set Bulk = Absorb = Float = 13.6 volts.

            If your BMS pulls ,8 amps is going to be the destroyer of your batteries. That means you are burning 250 watt hours a day as waste heat for nothing. Elite BMS systems are notorious LFP battery killers. Get rid of it, you have no need for it.

            FWIW to fully charge your batteries requires you to CC/CV at 14.4 volts and hold until the last cell charge current tapers down to 5% of C or 10 amps. So please explain how you will ever know when or if that happens if you are charging at 10 amps? Here is the problem, those Vampire Boards you got from Elite Power only bypass .3 to .5 amps when they turn on at 3.55 volts. That means you still have 9.5 to 9.7 amps flowing into fully charged cells. Your charger is not capable of controlling current when the first Vampire Board turns On to limit current to .3 amps. There is absolutely no reason to take your cells to 100% or even get close to 100%. All you are doing is cutting cycle life in half or more. Cut it to 80 to 90% and you can double to quadruple cell cycle life. Listen to Karak and you will kill your cells.

            As for what voltage you see during charging is a function of Charge Current and battery Internal Resistance. If Karrak really knew what he was talking about would know his cells are done. He cannot tell by looking at the graph his cell Internal Resistance has more than doubled in the one cell he is showing. He is looking at 3.25 Milli-Ohms in the graph. Hang around and I will teach you how to do that. Once you know the Ri of a cell, you can keep track of it and know when you have a problem. Karrak has a huge problem and does not know it. Keep in mind Karrak has been banned TWICE FOR POOR AND DANGEROUS ADVICE. So be careful.

            FWIW if your batteries were at 14.41 volts with 16 amps, you were severely over charging your batteries. Stop doing that. Lastly you cannot compare charging a Winston cell to a GBS Cell. They are not the same chemical makeup. Winston is LiFeYPO4 and GBS is LiFePO4.
            Last edited by Sunking; 06-18-2017, 11:11 PM.
            MSEE, PE

            Comment


            • #66
              That's what the Victron solar charge controller software said, but I'm not sure how that could be. It stated 249 watts, 27.6 v and 16.3 amps, which equals 449 watts. My panel is only a 300w
              Look carefully at your screen shot. Your batteries were getting 234.8W (the Array was producing 240W)

              PV:
              the 27.6V is the PV Array Voltage
              -------------------
              Battery:
              the 16.3A is the charging current @ 14.41A

              Beware the balance boards. Their shunt resistor is only good for about 1/2 amp and you were still pushing over 15A into the full cell.
              When a balance board fails, it drains that cell it's connected to, and then ruins it,

              You were Lucky - go buy a lottery ticket. And take anything Karrak says with a grain of salt. Take anything off the internet with a grain of salt. But I suppose someday we'll get the word to finally perma ban Karrak - till then we will continue to use him as an example.
              There are a half dozen flavors of Lithium batteries. Figure out what chemical mix you have, and use the settings for it, not what someone says works for their cells.
              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

              Comment


              • #67
                Originally posted by Sunking View Post
                You are letting terms confuse you.

                Bulk/Absorb = CC/CV Mode
                Float = CC/CV Mode.
                Perhaps so, or is that a typo? I thought Bulk was CC and Absorb and Float were CV. No?

                If your BMS pulls ,8 amps is going to be the destroyer of your batteries. That means you are burning 250 watt hours a day as waste heat for nothing. Elite BMS systems are notorious LFP battery killers. Get rid of it, you have no need for it.
                The BMS pulls 0.17 amps and the Tyco EV200 contractors (with the economizers) are around 0.2 amps each and there are two. The other 0.1 is from the LCD display. I have more solar and battery than I need and while I understand your sentiments about the vampire board's tendency to fail and kill a cell, I am new to this and the individual cell voltages and temperatures as well as the LV and HV cutouts seem like a worthy feature to have. I see them as training wheels. When I understand this a bit more perhaps I am willing to get rid of the protections.

                FWIW to fully charge your batteries requires you to CC/CV at 14.4 volts and hold until the last cell charge current tapers down to 5% of C or 10 amps. So please explain how you will ever know when or if that happens if you are charging at 10 amps? Here is the problem, those Vampire Boards you got from Elite Power only bypass .3 to .5 amps when they turn on at 3.55 volts. That means you still have 9.5 to 9.7 amps flowing into fully charged cells. Your charger is not capable of controlling current when the first Vampire Board turns On to limit current to .3 amps. There is absolutely no reason to take your cells to 100% or even get close to 100%. All you are doing is cutting cycle life in half or more. Cut it to 80 to 90% and you can double to quadruple cell cycle life. Listen to Karak and you will kill your cells.
                I don't think you read my post very carefully. I had to bring at least one of the four cells up to 3.55v (to activate at least one of the balance boards) for the BMS to initialize and start reporting SOC. I was standing right there when that happened and shut down the charging within about 8 seconds. I'm not sure how you could do it any more careful. I started this thread to learn how to maximize battery life so clearly this won't be my charging regime, but it did have to be done once.




                Comment


                • #68
                  Originally posted by Mike90250 View Post

                  Look carefully at your screen shot. Your batteries were getting 234.8W (the Array was producing 240W)

                  PV:
                  the 27.6V is the PV Array Voltage
                  -------------------
                  Battery:
                  the 16.3A is the charging current @ 14.41A

                  Beware the balance boards. Their shunt resistor is only good for about 1/2 amp and you were still pushing over 15A into the full cell.
                  When a balance board fails, it drains that cell it's connected to, and then ruins it,

                  You were Lucky - go buy a lottery ticket. And take anything Karrak says with a grain of salt. Take anything off the internet with a grain of salt. But I suppose someday we'll get the word to finally perma ban Karrak - till then we will continue to use him as an example.
                  There are a half dozen flavors of Lithium batteries. Figure out what chemical mix you have, and use the settings for it, not what someone says works for their cells.
                  Mike, appreciate the reply, but see my reply to sunking above. I was aware of the 1/2 amp limitation and disconnected the solar as soon as the first cell reached 3.55v.

                  Comment


                  • #69
                    Meh. words fail me. That's why I'm an engineer, not a salesman. Enjoy your batteries as long as last, and keep them away from flammable structures. Due Diligence done,
                    Nobody listens to an electronics engineer, when there's a good pitchman in the room. Sunking and I can go home now.
                    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

                    Comment


                    • #70
                      Originally posted by ASprinter View Post
                      The nominal specs are : Average 3.2 V (working) 3.65V-3.8V (peak ) 2.5 V ( cut-off low). The batteries spent several hours in the 3.3xV range and was only in the 3.4s for a short period of time and moving from 3.49-3.55 literally happened in a minute or two. As soon as the red light on one balance board came on at 3.55v indicating that cell's resistor was active, the capacity display that had been missing from the LCD monitor came alive. Literally within the 8 seconds or so it took me to throw a blanket over the solar panel it soared from 3.55 to 3.61V. I was shocked, but it didn't spend any more than a few seconds there, but the 3.8v cutoff was probably only a minute or two away at that point. After reaching that first initial full charge I put a load on the battery to bring the SOC down.
                      As someone who is responsible for designing two off grid power systems with LFP batteries that have both been in operation for over four years with little if any change in perfomance and who has done allot of research and testing of LFP batteries, I think I can safely say

                      Bad things will start happening if you charge an LFP battery to 4.4v-4.5V/cell. Even with this abuse it is unlikely that they will catch fire.
                      It will not damage them by charging to 3.8V/cell but doing so will reduce their lifespan. It is not good to leave the cells at 3.8V for an extended period (days) of time
                      If you want fast charging 3.6V/cell is a suitable charging voltage but charging at high rates will reduce their lifespan. Again leaving them at 3.6V/cell for extended periods will reduce their lifespan.


                      When you say "soared from 3.55 to 3.61V" you are only talking about a 60mV increase in voltage and still well within the safe operating range of the battery. If the battery was balanced by the supplier and the charge voltage was set to 14.4V I would think that the higher cell might have got to ~3.7V and the others would have caught up to around 3.55-3.60V before the charge controller went into CV mode and started to limit the current. Because you have in my view wisely installed a BMS the worst that could have happened is that the highest cell would have got to 3.8V before the BMS disconnected the battery from the solar controller and no harm would have been done. It is better to use the overvoltage relay to disconnect the solar panel from the controller rather than the the controller from the battery as the controller relies on power from the battery to operate.

                      That's what the Victron solar charge controller software said, but I'm not sure how that could be. It stated 249 watts, 27.6 v and 16.3 amps, which equals 449 watts. My panel is only a 300w.
                      This is the magic of an MPPT controller, they work by "converting" voltage to current by the simple formula VSolar * ISolar = Vbattery * Ibattery. In your case Vsolar = 27.62V, Vbattery = 14.41V, Ibattery = 16.30A so the panel current is 8.50A (14.41*16.30/27.62). It would actually be slightly more than this at the charge controller is not 100% efficient.

                      Sounds like a good approach. I'll start low, 13.8v and 10 mins of float and see where I end up.
                      If you want to be very cautious you could increase the voltage by 0.1V per day until you reach 14.2V.

                      That's what I thought too but the amperage coming from the inverter/charger is only matching the draw from the battery at the time; no charging. There is apparently a cc/cv mode that I have yet to find, so I am interested in researching that.
                      In the ME-ARC manual, is this the correct one? there is a whole section on setting up the CC/CV mode and setting up the different float modes. Your Inverter/Charger is very smart, impressive!

                      Simon

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

                      Comment


                      • #71
                        Originally posted by Mike90250 View Post
                        Meh. words fail me. That's why I'm an engineer, not a salesman. Enjoy your batteries as long as last, and keep them away from flammable structures. Due Diligence done,
                        Nobody listens to an electronics engineer, when there's a good pitchman in the room. Sunking and I can go home now.
                        Mike, Sunking, karrak, I am listening to all of you. You may have differing opinions but that is helping me learn. If my reply above seemed snarky I was just trying to point out that I charged to 100% one time because I had to, and I watched it like a hawk when I did it. I was not near disaster and I did not cause any damage to the batteries...one cell hit 3.61v for a few seconds, well within the operating parameters of this battery (3.8v is the cutoff). As soon as the BMS completed its full charge calibration I brought the batteries down to a much lower SOC. What you may not realize is this battery "kit" includes a 7" LCD monitor that tells me individual cell voltages and temperatures, pack-level voltage, amps in/out of the battery and calculated SOC in percent. The latter feature does not become active until you do one full charge. That's what I was doing. All features on the LCD now work as they should.

                        This is the magic of an MPPT controller, they work by "converting" voltage to current by the simple formula VSolar * ISolar = Vbattery * Ibattery. In your case Vsolar = 27.62V, Vbattery = 14.41V, Ibattery = 16.30A so the panel current is 8.50A (14.41*16.30/27.62). It would actually be slightly more than this at the charge controller is not 100% efficient.
                        Thank you for explaining that. Helps explain the numbers I was seeing on my clamp meter.

                        In the ME-ARC manual, is this the correct one? there is a whole section on setting up the CC/CV mode and setting up the different float modes. Your Inverter/Charger is very smart, impressive!
                        That's the one. I'm looking into this today and will report back. I bought this particular inverter/charger because it does have more user flexibility than others I have seen.

                        Comment


                        • #72
                          Set your Inverter LVD to 12 volts, Charge Controller to 13.6 volts and that is all you need once the batteries are balanced. Al that extra equipment you have will kill your batteries. Works for an EV, but not a solar system. You operate between 13,6 and 12 volts. Stay away from the knees at either end and your batteries will have maximum cycle life. Never let any cell go below 3 volts or above 3.5. If you Float at 13.6 volts, the batteries will saturate at 3.45 volts.

                          Head Mike's warning about Karrak. He is not welcome here and a fraud. The mods are itching to get rid of him permanently and using him as an example.

                          For a MPPT Controller use these formulas.

                          Output Current = Panel Wattage / Battery Voltage
                          Panel Power = Output Charge Current x Battery Voltage.

                          Be aware if you Top Balance like you are, you risk over discharging your batteries. Over discharge is instant death.
                          MSEE, PE

                          Comment


                          • #73
                            Originally posted by Sunking View Post
                            Set your Inverter LVD to 12 volts, Charge Controller to 13.6 volts and that is all you need once the batteries are balanced.
                            As we have discussed, the boating community thinks anything over a 13.3v float will overcharge the batteries. Can you help me explain how floating at 13.6v won't harm the battery? Here is the discharge curve for the GBS cells:


                            On paper, 3.55vpc is "full," and is the point at which the vampire boards turn on. According to the chart, 3.4vpc, which equals the nominal battery voltage of 13.6v you are suggesting, is also very close to a full battery.

                            Here are some screenshots from my BMS:

                            At 13.81V and at a 0.7A discharge rate the BMS is reporting a 100% full battery.


                            13.54V and 2.2A discharge reporting 99% full.


                            13.49v and 2.2A discharge reporting 99% full.


                            13.45v and 2.4A discharge reporting 98% full.

                            Can you explain why floating at 13.6v wouldn't leave me with a battery around 99% full? The answer is probably that I am discharging at way less than 0.5C and I have no idea how to extrapolate how that might look on the graph I posted. Thanks for humoring me with this.

                            Comment


                            • #74
                              First thing you have to understand is Floating; the battery is neither charging or discharging. There is no current. The battery is not charging or discharging.

                              In a working Off-Grid Battery Solar System, you are always charging if the sun is up, or discharging when the sun is up or dark. It never sits Floating in the technical sense. With your BMS, you always have a load draining your batteries. You will never Float in the technical sense. You are letting terms trip you up.

                              One thing you have not wrapped your noodle around is the difference between a battery that is Open Circuit Voltage (aka Floating on a charger), Charging and Discharging. All three are different voltages. You can have a fully charged cell that measures 3.6 volts when charging, 3.45 volts when OCV, and 3.0 volts when discharging. Look at your own graph and move away from the knees. Wished they showed OCV voltage because it is easier to see what I am talking about. Pick any point on that graph. For example the 50 AH discharge point (50% SOC) and look at the voltages. Dead center between the knees.

                              If OCV were printed would read 3.3 volts. (I will explain how I know that in a moment)
                              At .5c reads 3.25 volts
                              At 1C reads 3.2volts
                              At 2C reads 3.1 volts
                              At 3C reads 3.0 volts.

                              I know OCV voltage = 3.3 volts because from the graph I can calculate the battery Internal Resistance aka Ri = .001 Ohms which is what your batteries should be new. So here is the math and numbers.

                              .5C = 50 amps
                              1C = 100 amps
                              2C = 200 amps
                              3C = 300 amps.
                              Ri = .001 Ohms.

                              The Voltage of a Discharging Battery = OCV - [Current x Ri]. We can also say the OCV = Battery Voltage under Discharge + [Current x Ri] Simple high school algebra.

                              Now we can prove it anyway you want to spin it. I said the OCV is 3.3 volts or 50% SOC. Lets see if the math works.

                              Does 3.3 volts = 3.25 volts + [50 amps x .001 Ohms]? 0.5C curve
                              Does 3.3 volts = 3.2 volts + [100 amps x .001 Ohms] ? 1C curve
                              Does 3.3 volts = 3.1 volts + [200 amps x .001 Ohms]? 2Cc curve
                              Does 3.3 volts = 3.0 volts + [300 amps x .001 Ohms]? 3C curve

                              The answer is hell YES. to all above and true statements. It is right there on your own graph. So 3.3 volts OCV voltage on your batteries is roughly 50% SOC +/- 20%. That is exactly what your own graph is telling you.

                              Now the the voltage of a Charging Battery = OCV + [Current x Ri]. Exact opposite of a discharging battery. Again simple high school algebra

                              Take your same graph at 50% SOC or OCV = 3.3 volts; What is the voltage when charging at .5C, 1C, 2C, and 3C? You had better say

                              3.35
                              3.4
                              3.4
                              3.6

                              So apply your Boat Forum Logic. How is 3.3 volts 99% when on your batteries are 50% @ 3.3 OCV. 3.3 means nothing unless it is OCV. Depending on if you are charging, discharging or Floating. At 50% SOC can be anywhere from 3.0 to 3.6 volts. That is anywhere from dead to fully charged by Boat Forum and Karrak logic.

                              FWIW 13.6 volts is not engraved in Stone. Experiment and find the exact voltage for your batteries via Discharge Test. Charge them to 13.6 volts, and discharge them to 2.6 volts and measure the AH. If that is say 95 AH, lower the voltage a little and repeat until you get what you want. There is no exact voltage. You have to find it. 13.6 is safe. You may find 13.45 is perfect. Figure it out. But get rid of that BMS, it is a Vampire.
                              Last edited by Sunking; 06-19-2017, 08:17 PM.
                              MSEE, PE

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                              • #75
                                The math did it for me, that makes perfect sense and I really appreciate you taking the time to explain. That actually ties this whole thread together and explains some of the concepts I was missing.

                                I feel like I have a good handle on the solar, so now turning to my Magnum inverter/charger shore power source. If I use the "custom battery" setting it lets me set 13.8v absorb, float and equalize (eq can't be less than absorb) but absorb time is a min of 1 hr. I am guessing that absorb will be trying to push some level of amperage into the battery for an hour and that seems like a bad idea. There is a CC/CV mode that lets me set the voltage and has three options for terminating, Done Time, Done Amps or Hold VDC. Done Time is problematic because the minimum is 1 hr. Done Amps is problematic for two reasons, one is it seems I want to terminate charging before there is charge taper and second, Magnum doesn't recommend using this setting without their BMK (battery monitoring kit), i.e. the measurement via shunt. I looked into it and the shunt that came with my BMS is a 500A 50mV shunt and the Magnum shunt shares the same specs. A quick read on the internet makes it sound like I can have both my BMS and the Magnum BMK (which I did not buy) hooked to the same shunt. The third option, hold VDC, I'm guessing I wouldn't want to use with a LiFePO4.

                                Adding to the confusion the manual says that in the Done Amps setting you can set the Done Amps to 0 and that will keep the charger in CV charge mode until the Max Time setting is reached, and that is adjustable from 0.1 minute up. If it works the way I think it does, that might be the ticket.

                                I don't expect anyone to know the ins and outs of my inverter/charger, I'm probably just talking out loud here, but these options are discussed on Page 21 if anyone does happen to be interested. http://www.magnum-dimensions.com/sit...-ME-RC_Web.pdf

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