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Basic LiFePo4 purchasing primer

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  • Basic LiFePo4 purchasing primer

    The following is a basic expose on how to purchase LiFePo4 responsibly. It is primarily targeted towards those coming from diy high-school science projects, ebikes etc, and would like to know how it is purchased on a more serious level. It is not meant to be an end-all discussion on charging / operating lifepo4, which can be had in other threads.

    Primarily, we are [B]concentrating on large-capacity prismatics, gotten by legitimate businesses[/B] (examples later) who actually deal in batteries! This helps to assure that you are not getting counterfeits, manufacturer-recalls, used batteries, very-old-stock batteries, and so-called "recycled" batteries which lately can mean those involved in wrecks or just simply receiving stolen goods. I cringe when I see serious e-bike users shoot themselves in the foot by following the proper charging and maintenance techniques to the letter, only to be let down by sub-par and even dangerous junk batteries.

    [B]Small capacity "cylindricals" vs large capacity "prismatics" and also the C-Rate:[/B]

    For most solar housebanks or small projects where we aren't interested in cramming laptop-sized cells into every corner, large prismatics are called for. These large prismatics come in sizes up to 1000ah or so, and are about half the weight of lead, and about 2/3rd the size.

    Aside from them being smaller than lead, and having more energy density, prismatics offer the ability to SIMPLIFY and keep the cell-count down. Thus, a simple "nominal" 12v lifepo4 battery made with prismatics contains only FOUR cells. One of our members is running nothing but a 4-cell, 1000ah battery! (note that you don't want to go too far from a 12v standpoint or serious safety issues from that alone appear - regardless of chemistry). To do this with small cylindricals means keeping track of hundreds of series-parallel connections, each of which is an additional failure point.

    C-rate - our large prismatics are primarily sold and targeted towards the amateur EV crowd, and have anywhere from the ability to do short 3C to perhaps 10C bursts. Some small cylindricals can do even more! BUT, for any solar project of reasonable size, we DO NOT NEED high-current features. Thus there is no need to get small cylindricals, and in fact no need to get the very advanced lifepo4 variants either.

    The major players in the large prismatics are GBS, CALB, and Winston. There are others, but we'll concentrate on these for examples.
    But what do LEGITIMATE lifepo4 dealers look like?[/B] They don't come from salvage yards or pried-open laptops. Here is a small sampling of only 4 out of many available - I am not specifically endorsing any of them but using them as examples.



    Last but not least a "specialty" battery dealer (see my notes afterwards)

    WARNING - this last one is typical of what you may find from specialty houses dealing in all sorts of lithium chemistries. Remember, we are looking for "PRISMATICS" and not small cylindricals. At this retailer, the large lifepo4 prismatics you see are GBS brand, with blue cases and purple terminal top covers. You may see other lifepo4 batteries inside what *looks* to be a prismatic case, but may actually be super high-current small cylindricals inside. We don't need the added complexity and super high current capabilities that model RC'ers need for example. At places like these, you MUST NOT get confused with the different chemistries available.

    Other specialty retailers may look similar, but offer perhaps yellow Winston cells instead of GBS - that's fine. Tip: for experimenting with a small bank, I would suggest NOT using the 20ah sizes, regardless of manufacturer unless you absolutely have to. Reason being is that these may not represent the latest improvements made to the chemistries in models 40ah and above, and may not have the more exacting capacity and internal resistance matching that those 40ah and up generally tend to have. Workable - yes, and this tip may not apply in all cases. I'm just saying I would personally go no smaller than 40ah size.

    I chose to have mine delivered as a pre-made kit, fully wired, banded, bus-barred, terminal lugs etc, but did NOT choose any other additional circuitry since I wanted to choose my own external gear. Many houses also offer their own add-on stuff, like bms, balancers, and whatnot, but I would say READ here before you buy any additional componentry. Also be critically aware that some chargers you see from specialty sources can be nothing but warmed up lead-acid chargers whose voltages may not exactly be ideal for lifepo4 - typically too high for regular use - yet they may be within the EXTREME edges of the spec sheets. Use your knowledge before spending wads of cash.

    What do I need when ordering? [/B] So you are ready to order 4 cells to make a simple 12v battery perhaps. Is that all there is to it? NO - you need [I]additional hardware[/I] to reduce the temptation to jury-rig something together.

    The last thing you want to land on your doorstep is 4 naked cells. You also need BUSBARS to tie the cells together, and end TERMINAL CONNECTORS to actually attach your dc cables to!

    In addition, you'll also want them to be BANDED TOGETHER to prevent sideways torque from ripping terminals apart, and also to help keep the shape of the prismatics, especially large ones, from distorting in high-heat condtions, or in cases of mild overcharge. Which is covered in other threads so that you won't actually suffer from it!

    Note that many places already provide pre-built battery systems to do all this work for you. I just wanted you to know how it can be done in case somebody makes a mistake and needs to get individual parts.

    Unlike the early days, most legitimate businesses carry a range of stock that is either in house, in state, or stocked nationally, or at the very least in your continent. No longer do we have to have to wait for shipments solely from China directly, unless you are requesting cells that are very unique or are so popular that it is hard to keep them in stock.

    Terminal Covers - once you assemble the battery, the top terminals are basically exposed. It is up to the consumer or dealer to provide a safety cover to prevent anything from falling on top of them and shorting. Note that GBS cells (blue case / purple tops) each comes with a convenient plastic snap-on top cover for protection already. I recommend this to newcomers just for this feature alone, because if top terminal covers are the "round-tuit" option that never gets done until a shorting accident occurs, then GBS cells are your best choice.


    For those that want it, many of these places may supply their own version of a bms. However, like anything, some may prefer a 3rd-party one. These two are once again from legit businesses:

    [B]Note that I have purposely left out *detailed* charging, balancing, and other operating paramaters as I wanted to concentrate on primarily what one normally does to purchase lifepo4 from legitimate sources.[/B]

    The general rule for experimenters with ANY battery chemistry, is to start small with a "learner" battery where making big mistakes won't wipe you out. For instance, nobody in their right mind recommends a huge Rolls-Surrette FLA bank to a rank newcomer learning the ropes, and the same applies to experimenters with lifepo4. Start small to learn the ropes first.

    [B]WARNING - don't RUSH into a purchase![/B] Read threads a bit first.
    The reason for this is that if you rely solely upon some distributors little "faqs", they may contain STALE DATA from years ago, or represent voltages taken from the *extreme edges* of the spec-sheets, and are not typical for normal use. For instance, you do NOT want to take your *lifepo4* cells to 4.2v like pioneers did in the past at their wallet's peril! 3.6v is pretty much considered the MAX and most of us run conservatively at 3.5v and some even lower. Some chargers available at these sites may use the older voltages that are considered too high today - so look out for those or at least make sure you can adjust the voltage. Again, thread reading helps.

    Go cheap and you'll pay for it - in both safety and eventual replacements sooner than later. Why not do it right from the outset and not be tempted by "recycled" battery parts. Used Lifepo4 batteries that have suffered abuse from previous ownership may not be immediately detectable, and you can be just a few cycles away from a rapid and complete shutdown of the cell(s). Start out on the right foot by doing it right.
    Last edited by PNjunction; 07-20-2015, 03:51 AM. Reason: Added specialty house