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  • PNjunction
    started a topic Simplified lifepo4 charging and care

    Simplified lifepo4 charging and care

    Lifepo4 charging and care is actually very simple. In this example we are going to use a 12v battery made up of 4 cells, aka a "4S" configuration.

    We'll assume that you have purchased a pre-built battery from a reputable manufacturer a 4S configuration of quality CALB, GBS, Winston, Sinopoly, Hi-Power large prismatic cells, and NOT some random collection of RC modeling cells. Pre-built means that they have connected up all the cells with links, and have strapped the battery together for physical stability. Each cell is typically pre-charged to about 50% SOC before shipping.

    You'll need to babysit the very first charge, and accordingly have a voltmeter of decent quality.

    1) Upon receipt, measure the voltage of each cell. They should be relatively close to each other, somewhere around 3.2v. What we are looking for here are wide swings in voltage, like one cell reading 2v, and another reading 3.4v. Either that low cell is bad, or it just didn't get charged properly before shipping. Anything below about 2.6v upon receipt is a red flag. Having cells that read close in voltage upon receipt does NOT mean you have a good balance since during the flat part of the discharge curve they mean almost nothing. What we are looking for are wide variations for obvious signs of dead cells, or an indication that you may have received just a random collection that was put together.

    2) Set your AC charger or solar charge controller (disable any temp comp!) anywhere from 13.8 to 14.0v. There is NO NEED to set the charge voltage any higher. Those that do are trying to drive external balancing circuits, which can be additional points of failure. If you follow these precepts here, and of course are not using used/abused trash, but quality cells, there is no need for constant balancing. But don't tell them that.

    3) Apply the charge, and just make sure that no individual cell exceeds 3.6v during charge. If the cells are high quality like those above, and have been charged to about the same amount prior to shipping, ideally each will read very near 3.5v at the end of charge. If they are slightly out of balance, they might read anywhere from about 3.45 to 3.55v.

    So what is "end of charge"? Technically, that would be when the current to each cell drops to about 0.05C. But because we don't have to worry about sulfation, there is NO NEED to ever complete a charge to full! YOU decide where end of charge is, as long as it provides the capacity you need to get the job done without going beyond the low voltage limit upon discharge. This makes lifepo4 ideal for solar where obtaining a TRUE full charge is often not met. It has no problem with partial state of charge operations, and in fact prefers it.

    There is no need to go nuts over a small SOC voltage difference like this. No cell is above 3.6v, and due to minor differences in a cell's actual manufactured capacity and internal resistance, it is not uncommon for the SOC voltages to differ a little bit. Assuming you have quality cells, you'll still be able to achieve 80% DOD without suffering any major imbalance at the bottom end.

    4) Don't over-discharge. Set your alarm for a pack voltage of 12.8v under load. Disconnect them if they reach 12.6 to 12.7v under load. (3.15 to 3.175v per cell). This will be approximately 80% DOD, and you won't be travelling too far down the steep discharge knee. Because we are not going well beyond 80% DOD, small imbalances just before the knee drop are not that big of a deal. If you want to be conservative, just use 12.8v under load as a disconnect. Remember this: as solar users, we still should only design our systems not to use more than 50% DOD even with lifepo4. So go ahead and be conservative here.

    Optional: if you feel you must, or if your cells WERE somewhat charged hastily prior to shipment, and one cell wants to rise to 3.6v or more before the charge is finished, you can easily discharge that individual cell a little bit and check it again on the next cycle.

    In the case of my 20 and 40ah GBS batteries, this was nothing more than an RV incandescent brakelight bulb fixture. I "top balanced" them just for fun, even though it wasn't strictly necessary. When one cell was higher than the others, and when OFF CHARGE, I applied about 30 to 60 seconds of discharge to that cell. The battery quickly came into line after about 2 or 3 individual cell cycle/discharge compensation attempts. BUT note that it didn't change or improve things operationally! I was still stopping at a max of about 80% DOD, so nothing was really gained.

    What I am saying here is that upon receipt, with good quality cells and a decent charge from the factory, you may never have to "balance" at all!

    Is it that simple? Yes. Of course, most will want to use automation / relays for a low-voltage disconnect, like any other serious battery installation, but here I'm just showing how easy the majority of charging and care really is. In our application of being "fractional C", that is, low voltage and low current, there is no need to go nuts over balance as long as each cell rises no higher than 3.6v at the top, and just don't let any cell go below about 3.15v during discharge. That's IT!

    Individual cell monitoring? Sure, good stuff. But I consider that excessive since I don't (actually can't!) do that with my lead-acid batteries. If I suffer a dropped cell or other signs of poor performance, I'll be taking that up with the dealer / manufacturer much as I would with lead-acid, rather than hanging a rat's nest of wiring all over the top of my batteries - or worse yet letting an external balancing system fail or mask an issue that needs to be dealt with sooner than later.

    The overarching moral to the story is that we are NOT EV'er or RC modelers. OUR needs allow us the headroom to use lower charge voltages and conservative discharge depths. If you don't keep this in mind, you can easily be led astray by by those who operate in entirely different application scenarios.

  • Sunking
    replied
    Originally posted by karrak View Post

    If you don't want to float your LFP battery all you have to do is set the float voltage low as smily3 has said.

    I haven't seen any hard evidence that says that floating LFP batteries is bad for them. This information from A123 http://liionbms.com/pdf/a123/charging.pdf seems to indicate that floating LFP batteries is not bad for them. Google "Is floating LFP batteries bad for them?" for more information. I would be interested to see any evidence that backs up the statement that floating LFP batteries is bad.

    Simon
    WTF have I been trying to pound into your thick skull for a year?

    There is absolutely no difference between Floating a Lithium at something less than 100%, and two cells in parallel in any EV or laptop.

    Leave a comment:


  • karrak
    replied
    Originally posted by createthis View Post
    The thing I get most confused about with LifePO4 is the lack of charge controllers out there. Floating is generally considered bad with LifePO4, but there are very few charge controllers designed to not float a LifePO4 battery.
    If you don't want to float your LFP battery all you have to do is set the float voltage low as smily3 has said.

    I haven't seen any hard evidence that says that floating LFP batteries is bad for them. This information from A123 http://liionbms.com/pdf/a123/charging.pdf seems to indicate that floating LFP batteries is not bad for them. Google "Is floating LFP batteries bad for them?" for more information. I would be interested to see any evidence that backs up the statement that floating LFP batteries is bad.

    Simon

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  • PNjunction
    replied
    Originally posted by smily03 View Post
    Hmm, would it work to have the float voltage be something really low, like 11.5? Basically, get charged up, then the voltage drops off to basically nothing?
    Yes, that works if one is using a charge controller designed for lead acid. Two rules: NO temperature-compensation, so disable that. And, IF your controller drops back to 13.6v or less in float, then you won't run into issues.

    I know what Sunking is saying, but I'll still reference the term "absorb", as being 13.8v or higher, and when either a timer or current monitor trips, it falls back to 13.6v float - since we're shoehorning a Pb controller with an LFP battery.

    Ideally, no float at all, BUT if you have a sudden parasitic drain / minor ground short happen, that 13.6v float, might save the day - or at least prevent the bank from hitting the low-voltage disconnect.

    One just chooses which direction they want to take according to their needs.

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  • Sunking
    replied
    Originally posted by createthis View Post
    The thing I get most confused about with LifePO4 is the lack of charge controllers out there. Floating is generally considered bad with LifePO4,
    Who told you that silliness?

    A lithium battery charger is a Float Charger silly. Most Charge Controllers that will allow you to set voltages via keyboard down to 00.0x volts will work just fine. The Genasun controller is a float charger you set to 14 to 14.2 volts for LFP.

    The problem is you do not grasp how batteries charge. FLA and LFP use the exact same charge algorithm. Only the voltages change slightly to protect the innocent. A FLOAT CHARGER is a CC/CV charger. They mean the same thing. Every charge controller made is a CC/CV charger. Only thing you have to change is the voltage FLA = 14.4 to 15 volts, LFP 13.6 to 14.2 volts. All you need is a controller you can set the voltage down to 13.6 volts up to 14.2 volts in at least .1 volt increments, .01 even better.

    The only real difference is if you want to go to 100% with Lithium, you will need a way to terminate or turn off the solar controller when current tapers to 3/33 at 3.6 vpc. Genasun just floats below 100% at 14 to 14.2 volts. 14.6 is for 100% saturated to C/33.
    Last edited by Sunking; 07-19-2016, 05:48 PM.

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  • smily03
    replied
    Hmm, would it work to have the float voltage be something really low, like 11.5? Basically, get charged up, then the voltage drops off to basically nothing?

    Leave a comment:


  • createthis
    replied
    The thing I get most confused about with LifePO4 is the lack of charge controllers out there. Floating is generally considered bad with LifePO4, but there are very few charge controllers designed to not float a LifePO4 battery. The dinky little Genasun controllers and the Victron 100/30 100/50 series are the only ones I can think of, and I'm really just guessing because they have LifePO4 charging profiles (I have no idea how those profiles work under the hood). If you use the wrong charge controller, you need to wire a relay between the charger and the battery and shut it down when a certain voltage is reached, or you need to monitor it while charging, which is a bad idea IMO because humans make mistakes.

    I'm not even sure how that would work, because charging to 13.8v you'll hit 13.8v, but the resting voltage will drop you back down to 13.6v or lower, so it's like you need a high voltage cutoff combined with a state machine that only turns the system back on once it has dropped below a certain voltage. If you do that, you lose the ability to power things directly from the solar panels too.
    Last edited by createthis; 07-19-2016, 04:12 PM.

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  • karrak
    replied
    Originally posted by Sunking View Post
    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.
    There might be an imaginary universe made up by Sunking or maybe a parallel universe where NASA uses LFP batteries in its spacecraft, where LFP batteries don't go out of balance, where LFP batteries only last two and a half to five years, where charging an LFP battery to 100% will give you half the lifespan compared to charging it to 90%, where there is a 10% difference between charging and floating an LFP cell at 3.4 V/cell and 3.45 V/cell and where I make a commission out of selling cheap Chinese electronic goods. In reality, none of this is true.

    As for automation, I admit I am lazy. I would rather type in the Internet address of my or my friend's battery monitor on my phone or computer to check up on our batteries rather than grovel around on the floor in the shed with a multimeter or in the case of my friend's system, drive 150km and then have to measure sixteen voltages after having to take the plastic shield off his battery. I also like science, so I am getting logged data that will inform me how well LFP batteries work rather than just relying on hearsay.

    Simon

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

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  • karrak
    replied
    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

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  • PNjunction
    replied
    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.

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  • Sunking
    replied
    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.

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  • DanKegel
    replied
    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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  • PNjunction
    replied
    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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  • Mike90250
    replied
    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.

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  • DanKegel
    replied
    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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