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  • #91
    Originally posted by PNjunction View Post
    A big mistake with lifepo4 is thinking along the Pb lines, or the "drop in" mentality that salesman like to pitch.

    If we look at it from the typical 12v standpoint, the fellow in the article was doing the near equivalent of charging a 12v lifepo4 battery to 14.8v (3.7v per cell for a 4-cell lifepo4). BAD! That is near equivalent to using an AGM setting to charge your lifepo4 with. Not good. If one is going to wing-it with lead-based chargers, then by all means try to use the GEL settings, which are near 14.1v. Keep wallet open.

    Anyway, hats off to that guy for being a pioneer, sharing his experiences, and learning from them.
    I am kind of perplexed on Float Service. I visited a set of LFP's I installed for a customer over the winter. They are on a Outback Inverter with a Mate and FN-dc and hub. The system draws 60 watts on pass through, so if it's fully charged and left floating at some point during the week it will drop low enough to start using power to maintain the Float voltage. I set it up with the Float at 13.1v with a re-float of 12.7v over the winter without any load. The more I am thinking about this it may not be the best strategy. Now that summer is here the Inverter will have loads on it and the refrigerator will be a critical load, so shutting it off or by-passing is not a option.

    A bigger problem is the Bank will have to be fully charged prior to leaving the Marina. Generally people get to their boats and head out for the weekend, they won't be thrilled about waiting a couple hrs waiting on Batteries to charge.

    I think the Float / Re-float will accelerate the life cycles. Thoughts anyone ??

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    • #92
      You never float lithium batteries, that is a huge No-No. Just ask Boeing aircraft what happens when you do that. That is definitely stuck deep inside a Pb box.
      MSEE, PE

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      • #93
        Originally posted by Willy T View Post

        I think the Float / Re-float will accelerate the life cycles. Thoughts anyone ??
        Just keeping any Lithium chemistry battery at a voltage above about 80% SOC for any length of time will reduce your battery life, cycle or not.
        Going all the way to 100% SOC could cut your effective system life in half.

        The smart Lithium users (like Sunking, although he is mostly looking at EV applications) will try to keep the battery cycling between about 80% SOC and no lower than 20% SOC.
        If you have an application where power density and energy density are critical (EV racing for example) then you might want to go from 100% to 10% or less and accept the piss poor cycle life.
        The same person will also, for example, not be trying to maximize his tire life!
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #94
          Originally posted by Willy T View Post
          I am kind of perplexed on Float Service. I visited a set of LFP's I installed for a customer over the winter. They are on a Outback Inverter with a Mate and FN-dc and hub. The system draws 60 watts on pass through, so if it's fully charged and left floating at some point during the week it will drop low enough to start using power to maintain the Float voltage.
          Sure sounds like a parasitic load (monitoring gear doing that?), or perhaps a leaky ground? These guys may help you nail it down too, and this is not the only thread of interest...

          http://www.cruisersforum.com/forums/...nks-65069.html

          I set it up with the Float at 13.1v with a re-float of 12.7v over the winter without any load. The more I am thinking about this it may not be the best strategy. Now that summer is here the Inverter will have loads on it and the refrigerator will be a critical load, so shutting it off or by-passing is not a option.
          With whatever is causing that parasitic load, your sub-fully charged float voltage probably saved that bank - well before the lvd got to it anyway. 13.1 / 13.2 is not a high enough voltage to cause electrolyte heating in a float situation. Being set lower than fully charged means there is also no current flowing either. One has to carefully determine what the people mean by float - is that at LOW voltage levels, or do they mean floating at the HIGH voltage point, ie 14.0v or higher. If high, then that is not necessary and not good.

          A bigger problem is the Bank will have to be fully charged prior to leaving the Marina. Generally people get to their boats and head out for the weekend, they won't be thrilled about waiting a couple hrs waiting on Batteries to charge.
          That's up to them - if they want to forego a top-up charge prior to leaving after a long period of no use, and if they are interested in treating the battery with care for longest life, then they will have to oversize their capacity to run from say only 80% SOC initial charge when leaving. If they are visiting these things every week or so, then leaving them nearly fully charged will not immediately damage them and no top up required. What was inferred in that blog article, was that by trying to achieve extremely high voltage levels, (3.7v) and "floating them" at those high voltage levels, over time, added up to the equivalent of much more than just a week or two of leaving lifepo4 batteries fully charged.

          I think the Float / Re-float will accelerate the life cycles. Thoughts anyone ??
          Not so sure about the re-float, but yes, the relatively lower-than-full charge float voltage (13.1v total / 3.27v per cell) will not heat the electrolyte, and will serve as a "catch" for inadvertent low-level inadvertent parasitic loads for long periods of non-use. Better to arrive and top up for just an hour or so, rather than arrive with them all sitting at the LVD. Many might just argue to have a small generator handy on board just in case. Even better, find that parasitic load. One of the worst offenders can be the monitoring system itself. Just like vampire balancing boards, they can fail too and be a cause of imbalance. Hardcore users will dedicate a much smaller dedicated battery to power the monitors just in case, and not tap off the main bank.

          Here again, the application in mind demands a different set of paramaters that only the end-user can determine or live with.

          Remember too that a charge voltage is vastly different from a voltage at rest (24 hours or longer). That is, you might achieve a full charge up to 3.6v / 0.05C, but when left for 24 hours, it will settle to anywhere from about 3.38v (older GBS cells) to perhaps 3.45v and have full capacity available.

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          • #95
            Sure sounds like a parasitic load (monitoring gear doing that?), or perhaps a leaky ground? These guys may help you nail it down too, and this is not the only thread of interest...
            Yes it is. With 3 powered devices, plus the inverter that use power from the bank when on shore / grid power. Xanterx and Magnums are the same, they all use battery power on Pass - Through.

            I havn't timed the charge cycle from 12.7v ( re-float ) to 13.1v ( float ), but lets say it's 30 minutes. To me that is a cycle, but what is it to the batteries ?? I can set it so the Inverter charges to a fixed voltage of say 13.2v and just let them float. I am just trying to see whats better. I could set the float / re-float so it just does a full cycle ( 12.7v to 13.8v ) and forget it.

            I probably could get around the Fully charged ( ready to go ) on Friday with the AGS exercise period that day with the grid, instead of the Generator. I thought about a small battery maintainer paralleled on to the system to cover the parasitic load, just trying to come up with some work arounds. A VCS ( voltage controlled switch ) could be added with a stand alone charger to manage a charge cycle, again more complexity and a point of failure. I thought about just a simple timer and do a charge cycle once a week.

            This just something that comes up when you start changing one technology for something else and the unintended consequences. I vowed to myself to give them a chance, this just another problem I didn't envision.

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            • #96
              I do not think anyone has asked this question including myself Willy; but are we talking about Lithium Iron Phosphate (LiFeP04) batteries?
              MSEE, PE

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              • #97
                Originally posted by Sunking View Post
                I do not think anyone has asked this question including myself Willy; but are we talking about Lithium Iron Phosphate (LiFeP04) batteries?
                I've been following along, and I was wondering that. In post #91:
                I am kind of perplexed on Float Service. I visited a set of LFP's I installed for a customer over the winter.
                I think this is the bank being discussed.

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                • #98
                  Originally posted by Sunking View Post
                  I do not think anyone has asked this question including myself Willy; but are we talking about Lithium Iron Phosphate (LiFeP04) batteries?
                  Yes, 8 x 260 amp hr ( 520 amp hr, 4s2p ) batteries in 12 V configuration.

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                  • #99
                    Originally posted by Willy T View Post
                    Yes, 8 x 260 amp hr ( 520 amp hr, 4s2p ) batteries in 12 V configuration.
                    OK I am going to butt out of this one, I don't want my name associated with it. Hint 13.1 volts.
                    MSEE, PE

                    Comment


                    • Originally posted by Sunking View Post
                      OK I am going to butt out of this one, I don't want my name associated with it. Hint 13.1 volts.
                      Ok, I won't mention it. It seems safe, it's darn if you do or darn if you don't. I am sure this will come up for anyone using a on Grid stand by, unless they can disconnect from the bank.

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                      • 13.1v after a full charge would be fine - BUT that is after a full charge to a higher level.

                        One should be careful to define if their battery is in regular use, or in a backup state. Lifepo4 likes to be used, and does not like sitting around fully charged for any great length of time. Thus, if your solar operations are blessed enough to put them into more of a "backup" category, then lead-acid is the better bet sitting around fully charged!

                        If you fall into this category of very shallow-cycling / backup, question the wisdom of using lifepo4 in the first place.

                        Back to voltages - anything 3.45v or higher per cell will *eventually* fully charge a cell. At 3.45v it just takes a bit longer (assuming you supply at least 0.05C to begin with) than doing it with say 3.6v.

                        Thus, I could "float" my lifepo4 battery sitting at 13.8v, but if I don't use it, it will sit around fully charged - not good. Better to use Pb in that scenario, unless the other factors of lifepo4 make it worthwile - weight, size etc. That would be a hard sell considering the capacity loss over time from secondary reactions that takes place sitting around fully charged.

                        In the setup described earlier, IF YOU DON'T fully charge the battery all the time, and it is not going to be used often, a safer bet is to be VERY conservative, and run say 13.6v max (3.4v per cell), which is not enough to fully charge the cell even if given time. Of course, you should plan your capacity needs appropriately derating your cells a bit, or actually measuring the discharge capacity. STILL, you are sitting around on the high side - not 100% SOC, but a bit lower. That's good but one is now faced with the practical cost of essentially oversizing their bank to just sit around doing much of nothing. Pb could make much more sense as long as you have the maintenance capability.

                        Once again, before shelling out the huge bucks and making a big mistake, get a small 4S lifepo4, say 40ah or so, and test it yourself to get comfortable with it and be able to prove / disprove all this in front of your eyes.

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                        • PN there is one huge issue using LFP with Solar Charge Controllers. As you noted you can FLOAT a LFP battery indefinitely, but it has to be at a voltage less than 100% SOC. In my book no higher than 90% and that can be asking for trouble if you have any imbalance or use top balance.

                          Problem is all but a few charge controllers have switch selected battery type of gel, agm, and fla. All three of those algorithms use 3-Stage and all three stages are greater than 100% LFP. Bulk and Absorb are well above 100%. To compound the problem all solar CC's cycle every 24 hours and automatically run through all 3 cycles starting at sun up.

                          There are only a handful of CC's that you can set Bulk = Absorb = Float = 90% SOC for LFP. All done by software through a keyboard. So unless you have Midnite Solar or Outback CC you are SOL. Those are the only two I know that can do that. That has to do with a Midnite Solar is nothing more than an improved Outback designed by the same engineer. I don't hink MorningStar has that capability.

                          Bottom Line Lithium batteries are the easiest to charge because all you need is a Float Charger. Having said that nothing is better for Pb than a Float charger. 3 and 4 stage is useless for solar. I don't know why manufactures have not figured that out yet. They could make a much less expensive and less complicated product that could work for both Pb and LFP easily. Plum crazy thinking.

                          MSEE, PE

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                          • MorningStar controllers (the larger MPPT ones) are fully programmable for time and voltages at all stages. I throttle mine back over the summer to save on water in the batteries.
                            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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                            • Originally posted by Mike90250 View Post
                              MorningStar controllers (the larger MPPT ones) are fully programmable for time and voltages at all stages. I throttle mine back over the summer to save on water in the batteries.
                              Great I will remember that. It makes them doable.
                              MSEE, PE

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