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  • #31
    Sunking Battery Rule # 84

    PN thought I would share with a useful battery rule you might find useful. To accurately compare a FLA to LFP we need to find a common denominator between the two types to be equal in application. For RE application the standard is 5 day autonomy using FLA with 50% usable. Let's say a 100 AH FLA battery would have 50 AH usable. So what size LFP is equal to that under the same criteria of maximum cycle life. Well the Answer is:

    Sunking's Battery Rule #84

    That rule states for every 100 AH of FLA battery takes a 84 AH LFP to be equal or 84%.

    If you operate a 84 AH LFP between 80 and 20% DOD or SOC whichever way you want to look at it will equal a 100 AH FLA operated from 100 to 50% SOC. Both have an equal usable 50 AH.
    MSEE, PE

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    • #32
      Thanks Dereck. Math Rules!
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #33
        new solar panels.jpgfront bay.jpgManzanita small.jpgthe big woods.jpgControl panel.jpg
        Originally posted by SunEagle View Post
        Reed

        Care to share any pictures of your battery system?
        Sun Eagle

        Think all the attachements are there:

        INTERIOR MONITOR PANEL
        This is on the same panel as everything else for the 5th wheel (slides, interior/exterior lights etc)

        Upper black monitor on left is Magnum inverter and charger on/off switches and voltage for bank

        Lower black monitor is Manzanita Micro and gives voltage of each cell, total voltage, charging/discharging rate in watts and amount of Wh below full charge

        Lower white monitor is Tristar giving charging rate in watts and amps (at 48 V nominal).

        Lower device is to run outside "party lights"

        PHOTO OF SIX PANELS
        These are six 235 W Panels ganged in two sets of three each in series. Voltage to Tristar MCCT-45 is around 90 V (maximum of 1300 W) so amperage is about 14 amps. We were in wreck between Vera Cruz and Puebla last year that totaled pickup (GMC 6.6 l 4x4 diesel) and 5th wheel. Solar was still working well, batteries were in place and there was no discernible damage to panels (4 panels then) and they were still tightly in place. We have room for three more panels but see no need for such.

        PHOTO OF MANZANITA MICRO 180 Ah 12V nominal battery
        This is composed of four cells in aluminum box with Lexan cover and full BMS

        PHOTO OF FRONT BAY
        Bay was designed to hold an Onan 6.5 kW propane generator. Called Open Range for weight limitations and they said it should hold 400 pounds. There are four Manzanita Micro batteries in series to make a 180 Ah 48 V nominal battery bank (720 Ah 12 V equivalent). 4.0 kW Magnum PSW inverter is bolted to top of bay. Tristar MCCT-45 Controller is to its right. Since the voltage from panels is around 90 V, the amperage is only about 14 V.

        There are two battery chargers with total power of 1500 W. Son put these in since we have had real problems with "dirty" voltage in Mexico. Burned out micro-waves in lower Baja and Yucatan. Have dumped 50 amp cable and will probably dump 30 amp cable since we shall probably never need more than the 15 amp power cord. Son did rewire so that the 50 amp inlet will run AC only if we ever need to be where air conditioning is necessary all night - just leave Dodge is our attitude.

        There are the usual peripherals in there as well.

        PHOTO OF CG IN OLYMPIC PENINSULA RAIN FOREST
        Solar does not do much here. Lasted six days on LFP alone

        Can easily send more information via e-mail if you wish.

        Reed and Elaine

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        • #34
          I like rule #84!

          It pays to be conservative. Fortunately with lifepo4, if you change your mind and want to run from 100-20% SOC, you can do so, perhaps you envision some temporary extra loads, or are entering periods of poor solar-insolation etc and want to put a genny on it) and later go back to more conservative values. With lead, you are stuck with 50% DOD max for the most part.

          Without sulfation to worry about, it opens the doors to a lot of different operational avenues, whether by design or by luck. Fortunately, if you make a mistake and over-size your capacity, you'll just have additional autonomy, which might take the sting out of realizing you just burned a hole in your wallet by not accurately measuring your power needs up front.

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          • #35
            PWM controller for 'drop in replacement' LiFePO4

            I'm considering buying this battery as my entry into LiFePO4.

            http://store.starkpower.com/12V-12Ah...tery_p_22.html

            The solar charger 1) has to have a settable lvc and hvc 2) be able to disable equalize mode 3) No temp control 4) NOT float?? 5) ?

            Anyone have a recommendation of which pwm to choose? I asked the manufacturer of the batts - they said 'morning star' http://www.morningstarcorp.com/produ...e-controllers/)

            I have 200w of panels.

            Thanks, Paul

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            • #36
              That's pretty typical for the "drop in" mentality crowd.

              I ask myself though - who makes the actual internal cells? Is it high quality like A123, or from some unknown source? Is it subject to change depending on market pricing alone, or do they stick with a KNOWN quality manufacturer? For people that know LFP, will they cry if they cut one apart?

              Since you don't use temperature compensation with lifepo4, which the morningstar's have, that raises a red flag right there on their knowledge.

              However - I get it. They are relying on their bms / internal bleeder boards etc to do all the heavy lifting when an end user applies a charging source which is not really applicable for lifepo4 in the first place.

              Give it a shot - just cross your fingers that the internal bms doesn't fail. Maybe it won't.

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              • #37
                Originally posted by PNjunction View Post
                That's pretty typical for the "drop in" mentality crowd.

                I ask myself though - who makes the actual internal cells? Is it high quality like A123, or from some unknown source? Is it subject to change depending on market pricing alone, or do they stick with a KNOWN quality manufacturer? For people that know LFP, will they cry if they cut one apart?

                Since you don't use temperature compensation with lifepo4, which the morningstar's have, that raises a red flag right there on their knowledge.

                However - I get it. They are relying on their bms / internal bleeder boards etc to do all the heavy lifting when an end user applies a charging source which is not really applicable for lifepo4 in the first place.

                Give it a shot - just cross your fingers that the internal bms doesn't fail. Maybe it won't.
                Hmmm, not exactly a ringing endorsement. Perhaps I'll take a different approach instead. Appreciate your honest, level headed guidance PNJunction. Paul

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                • #38
                  Note that I'm not saying that approach won't work. And since I have no experience with Starkpower, I'm not calling them out directly. I'm just saying buyer-beware. There are a bunch of guys throwing substandard cells into tupperware boxes and slapping their sticker on it. Obviously, Starkpower does not appear to be like that.

                  In the motorcycle world, a similar approach is taken by the LFP EarthX batteries, which are very good. Great for those who just don't want to touch their regulators and so forth, are prone to leaving the lights, glove heaters, radios on etc, and killing LFP batteries without any sort of lvd.

                  In a similar veign, the "drop in" mentality for the Pb crowd, is what burns up gel's, and undercharges agm's, when bike owners don't set their regulators properly when they change even similar chemistries.

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                  • #39
                    Has anyone seen this writeup: http://ka7oei.blogspot.com/2013/05/l...e-lifepo4.html ? It's quite a detailed page about one guy's experience with LiFePO4 batteries and balancing.
                    Last edited by Mike90250; 06-18-2016, 04:57 PM. Reason: approved

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                    • #40
                      Originally posted by DanKegel View Post
                      Has anyone seen this writeup: http://ka7oei.blogspot.com/2013/05/l...e-lifepo4.html ? It's quite a detailed page about one guy's experience with LiFePO4 batteries and balancing.
                      Be sure to note all the precautions taken to prevent shorts, damage and fire. Even small batteries (like phones and laptops) can easily start a fire or cause a burn, overheated wires will surely do the same too.

                      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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                      • #41
                        I've seen KA7ZOI's LFP experiments, and unfortunately, it is all over the map.

                        He uses a CBAIII analyzer, but does he know that there is a 0.3v difference between what the CBA records as voltage and what is actually at the terminals? (can you smell a diode in the CBA circuitry here?). Noticed that right off the bat with my CBAIV, so I adjusted accordingly - and used a *trusted* voltmeter like a Fluke to tell me so. That would be a big problem if he ever bottom balanced at 2.5v, and was really doing so at 2.2v or even more!

                        There is also the problem of an experience with basically "toy" LFP batteries, unlike those from CALB, GBS, Headway etc in formats that are much easier to get lined up without tearing into a water-bottle battery. Problem is, LFP at those small cell capacities are outrageously expensive - nearly twice the already astronomical prices of larger prismatic formats. Been there with Shorai's, which already have convenient balance lead wiring.

                        Ironically, keeping a 12v LFP battery balanced without a lot of spaghetti-circuit wiring is not a big deal for a ham radio op (or shouldn't be) - as long as one knows how to either top or bottom balance - your choice. BUT, here we see the marketing influence of the need for a balancing circuit, (aside from common sense LVD or HVD's) which this demographic can fall for very easily since it is more gadgetry to have fun with.

                        Also appearing is the notion that voltage alone determines charge soc, when in fact, *saturation* or absorb current from 3.45 to 3.7v will achieve the same, the only difference being the time it takes to absorb. Still stuck in the PB voltage-is-everthing world I'm afraid.

                        Yep, it promotes the idea that it is wise to put a 5-cent or even 5-dollar balancing circuit, which in many cases is not accurate, or goes innacurate over time, killing expensive prismatics. Water-bottle batteries - ok, just toss/recycle and replace. Questionable cells in this super-small toy/hobby market may actually need a full time bms nanny, so there's that rub!

                        Knowledge about 12v LFP batteries, keeping it simple and conservative, and starting out with quality cells to begin with, (as long as you have access to each cell) along with proper wiring infrastructure and initial charging goes a long way - unfortunately, most in our demographic never take the blinders off and slap junk on the cells, promoting the very problem we are trying to avoid in the first place.

                        Not necessary if you know what you are doing, but I guess it feels good. I have no ill-will for that guy's experiment, he just fell for the problem of the cells not being balanced *in the first place*, along with some owner-abuse, and now needs a balancing nanny circuit. If only he had started on the right foot.

                        He just didn't know that provided the cells are quality, he could have just used a simple variable-voltage bench supply for the canonical so-called top balance (initial individual charge on each cell) and be done with it. Once proven, he could delve into bottom-balancing just as easily - all without any spaghetti balance board circuitry since he obviously has the skill to do so. He just doesn't know.
                        Last edited by PNjunction; 06-25-2016, 10:13 PM.

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                        • #42
                          Thanks. Did you bring up any of these issues in a comment on his page? He and others reading his page might appreciate the info.

                          And/or what's the best sticky on the topic? (um, I guess it's this one...?)
                          Last edited by DanKegel; 06-26-2016, 01:54 AM.

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                          • #43
                            Originally posted by PNjunction View Post
                            Ironically, keeping a 12v LFP battery balanced without a lot of spaghetti-circuit wiring is not a big deal for a ham radio op (or shouldn't be) - as long as one knows how to either top or bottom balance - your choice. BUT, here we see the marketing influence of the need for a balancing circuit, (aside from common sense LVD or HVD's) which this demographic can fall for very easily since it is more gadgetry to have fun with.

                            Also appearing is the notion that voltage alone determines charge soc, when in fact, *saturation* or absorb current from 3.45 to 3.7v will achieve the same, the only difference being the time it takes to absorb. Still stuck in the PB voltage-is-everthing world I'm afraid.
                            Well said and is what I have said many times in different ways. It comes from the Pb mentality one must fully charge a battery which is nonsense with respect to Lithium Ion batteries. It f you are building a commercial product you have absolutely no choice as a manufacture other than to use automated charging from a product liability POV and Ignorant Joe Public. Not to mention all the up-sale that comes with it.

                            FWIW I think you can expand that to include 24 volt or 8S, and to some extent 48 volt 16S. At 12 or 24 volts of a conscious person with heartbeat and knowledge of a lithium battery can easily determine the battery health with just a glance of the pack voltage. You only have a usable range 12 to 14 volts on a 4S system and will darn well notice a 3 volt error. If you see something below 12 volts will get your attention real dang fast. A simple LVD built into an inverter, and strategic charge regimen is all one really needs to protect his/her battery. All it takes is some knowledge and understanding.

                            Now for the Dan's and Karrak's out there, you need all the help you can get in the form of automation and need a Nanny Device to control your life. Karrak needs it for his commission, and Dan needs it because no one can think for themselves.
                            Last edited by Sunking; 06-26-2016, 11:49 AM.
                            MSEE, PE

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                            • #44
                              Erm - cool. I think the major problem is that there is so much info out there, a newcomer doesn't know who to believe, nor have the lifetime or stomach to do stuff like I do like read 3000-message long threads still active 5 years later.

                              I think it would have to be an example project to be the most instructive. For example, how to use say an iCharger like my 306B to do your build / balance / test. And how when using a 1S connection like I do for both individual initial cell charging, and later pack charging, how FAST is actually *slower* than Charge, if you do the math right.

                              Now THERE is a gadget which would draw some good attraction (likewise a PL8 or similar) for us in that demographic. Just be aware that the canned presets are not always the best!

                              I just dont have the words how useful these higher-quality hobby chargers are to get your battery in condition to prepare for an eventual solar charge.

                              I just wish something like this was a sticky or something - maybe complete with a screen-grab(s). Once it is visualized, then the light-bulb goes on.

                              I just get too tongue-tied to do a proper writeup about it. I was asked once by an organization to do it, but declined because I KNOW I'm not a good technical writer.
                              Last edited by PNjunction; 06-27-2016, 12:51 AM.

                              Comment


                              • #45
                                Originally posted by Sunking View Post
                                Well said and is what I have said many times in different ways. It comes from the Pb mentality one must fully charge a battery which is nonsense with respect to Lithium Ion batteries. It f you are building a commercial product you have absolutely no choice as a manufacture other than to use automated charging from a product liability POV and Ignorant Joe Public. Not to mention all the up-sale that comes with it.
                                As I have said on many occasions before, charging an LFP battery to around 99+% has not been shown to significantly reduce its lifespan. If you have an off grid system that is relying on solar power to charge it you want to have your battery as full as possible at all times there is sunshine to tide you over the cloudy days. Not much different to making sure that your car is full of petrol if you are driving somewhere and don't know how far it is to the next petrol station.

                                FWIW I think you can expand that to include 24 volt or 8S, and to some extent 48 volt 16S. At 12 or 24 volts of a conscious person with heartbeat and knowledge of a lithium battery can easily determine the battery health with just a glance of the pack voltage. You only have a usable range 12 to 14 volts on a 4S system and will darn well notice a 3 volt error. If you see something below 12 volts will get your attention real dang fast. A simple LVD built into an inverter, and strategic charge regimen is all one really needs to protect his/her battery. All it takes is some knowledge and understanding.
                                The three volts you talk about is to avoid a disaster when you are discharging an LFP battery. When charging the margin is only one volt. 4.5 volts on any cell will severely damage it. Leaving an LFP cell at or greater that 3.65V or less than 2.5V for any length of time will damage it. This gives you a margin of error of only 0.2 volts when charging and only 0.5 volts when discharging.

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

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