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Thread: Lithium/Iron Battery Primer (LiFePO4)

  1. #1
    apriliaforum expert TimeBandit's Avatar
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    Lithium/Iron Battery Primer (LiFePO4)

    I thought I'd write this Primer on Lithium Fe(iron) Phosphate (LiFePO4) battery packs. LFPs are emerging onto the market fast and there still seems to be very little understood about this technology by both consumers and (shame on you) manufactures & vendors.I just wanted to compile a common dumping ground here to serve as a starting-point for anyone interested, or already owning this technology by outlining a couple do's and don'ts, misconceptions, caveats, along with some best practice advice. That said, this is (I am) not the definitive guide on LFP packs. Best to conduct your own research and draw your own conclusions.

    So... you want a LFP battery? Maybe you already own one??

    It's light !! - Perhaps the biggest marketing lure is the huge weight reduction, in an average 10lbs less than lead-acid. Other advantages might include, more cranking power, less voltage sag during starting (great for F.I. bikes), true dry battery (mount any direction), and longer ownership life.
    Longer life is what is prompting this primer, because unless one fully understands how to properly own this technology, you have (ironically) a higher probability of prematurely shortening the life of a LFP.

    Lithium-Ion - Don't let the word Lithium scare you of melt-downs, fires, and explosions. These are not the same as in your typical cell-phone/laptop batteries. These lithium's implement Iron (not cobalt or manganese), and are said to be the safest within the lithium-ion family.

    Dry Battery - Perhaps a big contributor from being so light, these are truly dry-cell batteries. The chemicals used are tightly packed and are in a "dry" state - hence the battery can be mounted in any direction. But this dry tech has a major draw-back, read-on ...

    Bad News:
    Let's get right to it. There are some draw-backs "if" you intend to get long life out of your LFP pack. After all, you wouldn't just inflate a tire and never routinely re-check/adjust the pressure. That said, *most* LFPs involve a little more attention, monitoring, and/or "smart" electronics.

    Issue #1 - Under-Voltage :
    Back to our tire analogy ... operationally, a tire has a narrow "safe" pressure range. Too much PSI might blow the tire, while too little might fatigue the tire. In either case, the tire is toast!
    LFP cells equally have a safe operational range, aka its voltage range. Sure, we all know over-charging any battery is bad-news, but LFP's introduce a new potential of damage --> under-voltage. In fact, it is just about as equally bad as over-charging! The reason is that the chemistry inside the cell is tuned to its ideal operating voltage (roughly 3.6v), thus deviating voltages either too high or too low can result in damaging the cell's internal chemistry - permanently! True, while lead-acid cells are also vulnerable to under-voltage conditions, they can a) tolerate much much lower voltages and for longer durations, and b) are likely recoverable using desulfator charges. Contrast in that LFPs are not - once damaged, stays damaged. Furthermore, say one cell does get damaged, it can then act as an internal load slowly draining the entire pack, subjecting the remaining cells to harmful under-charge. Easy to see how this can quickly become a cascading failure and thus prematurely rob you out of your investment. Therefore, the key to protecting your LFP is to KEEP IT CHARGED - ALWAYS.

    One good thing about LFPs is that they maintain their charge way better than any acid battery. BUT, that only applies to sitting on a shelf unconnected! So, I emphasis this under-voltage concern because it's probably way more likely to happen than you over-charging, because limits in our vehicle's charging system do offer some protection. Yet there is NOTHING to protect against potential under-charge conditions while connected to your bike. The reason is that most modern vehicles today constantly draw "some" type of current from the battery at all times even with the ignition key out/off. I like to refer to this as parasitic-drain, and the main culprits being the ECU sleep power, immobilizer, security standby alarm, added accessories, etc... and given enough time, your bike can bleed the LFP pack dangerously low. Remember, today's bikes are designed with a lead-acid technology in-mind, and lead-acids will 1st fail to turn your engine over long before the battery reaches damagingly low voltage states. Contrast this with a LFP pack; while it may still start the bike in its low-voltage state, every minute that battery is in that low state puts chemical stress on the cell's internals.

    Issue #2 - cell-drift (aka unbalancing) :
    This is actually tied to the same narrow operational voltage problem just discussed above. Packs are comprised of series individual cells. Since our vehicle charge/discharge to the whole pack, it's up to these cells to work-out their share within the series, and that is the core problem. While we like to think all cells are created equal – they're not. Slight material and chemical differences in cell manufacturing causes various internal resistance and capacity variances from cell to cell which unfortunately dictates how each cell in a pack is likely to give/accept a charge, etc... The result after constant charge/discharges can cause cells to drift to higher and lower voltage states. This can occur unnoticed as the total pack voltage output 13.8-14.4v (fully charged), yet some of the individual cell voltages to drift to their respective high & low extremes. We call this condition an unbalanced pack, and LFP's are very susceptible to it. Left uncorrected, the individual cell voltages could be all over the map (high/low), and thus being subjected to chemical stresses that may result in damage/failure.

    Ah, but don't fear. There are solutions to offer protection, aka Balance Chargers (b-chargers), and/or added "smart" electronics inside the pack itself to enforce that each cell stays within its appropriate voltage states, etc... More on this later.

    [...continued...]
    Last edited by TimeBandit; 02-04-2014 at 11:28 AM. Reason: revised facts

  2. #2
    apriliaforum expert TimeBandit's Avatar
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    LFP Pack configurations

    LFP Pack configurations:
    Since each cell has a narrow voltage-range, one must connect an array of cells together to form the final output voltage necessary. In our case, we're looking for 12.8-14.4v on our bikes. Ideally, 4 LFP cells in series offers roughly 13.2 volts (given 3.3v each, depending on charge-state and cell manufacture).

    [See attached]

    To Be or not To Be?? More like, To Protect or not To Protect (the pack) – that is the question.

    Fig 1 shows the most basic of configurations, but offers no high/low voltage protections, nor does it allow one to insure the pack stays well balanced, or the ability to re-balance. That said, if you like playing roulette; this is a great design ...... NOT! Although this design works fine, and may work fine for a long time, it offers no guarantees and whole hell of a lot of assumptions! It is probably the worst implementation as the risk of under voltage bleed-down and cell unbalancing probability is very likely in the long-term.

    Fig 2 offers a Battery Management System (BMS) port, which is a big step forward. Aside from being able to monitor the individual cells, you can opt-out of using whole-battery charger and instead get a balance charger (highly advised) which uses this port to charge each cell individually. However, we are still lacking under-voltage protections for the whole pack, but at least the BMS port allows one to add some such mechanisms/circuits externally. More on the BMS port a little later.

    Fig 3 shows a pack implementing Smart Balance Modules (SBM). There is one module connected in parallel to each cell, and all it does is prevent cell over-voltage protection. SBM's can offer you the freedom to still utilize a whole-battery charger (aka 13.6 volts), making this pack more friendlier to your vehicle's charging system, thus not worry about the possibility that a cell or two drifts dangerously high, or ends your battery charge prematurely before other cells in the array are yet fully charged. The only reservation I have about implementing SBM's is insuring their compatibleness with “dumb” nature associated with all vehicle charging systems, being that most SBM's protect the cell by shunting excess current to it's neighboring cells. So, what happens when the vehicle's float charge voltage-levels eventually cause all the SBM's to enter shunt mode (i.e. charged battery)? Is that simply “seen” as a constant load on the alternator? Does it stress the SBM's, etc... my Jury is still out on that one - further testing is warranted.

    Fig 4, Yes, there's always a "Cadillac" option, isn't there. Here we see a pack designed around a Protection Circuit Module (PCM) which offers per-cell balancing, over-voltage safeties, and the very much needed under-voltage protection. Notice this pack does not have the typical two-post ( POS & NEG terminal) connectors, rather they have 3 (sometimes 4) terminals. Usually one ground and two positives; or one positive and two grounds. Either way, the configuration offers a "protected" terminal designated by (P) which is automatically disconnected in the event the battery voltage gets too low, charge is too high, and/or discharge rate is too much. Because the "P" terminal limits current rate, a proper amp-rated PCM should be considered, and perhaps by-passed for the starter – hence is why the (B) terminals are still accessible. I'll supply a pic on this a little later.


    [...continued...]
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  3. #3
    apriliaforum expert TimeBandit's Avatar
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    Cell quantities greater than 4

    Cell quantities greater than 4:
    The BMS port offers electrical pathways directly to each cell. At the time of this writing, there are few commercial LFP pack vendors, of them, some offer the port, and some don't, and of the some that do, seem to be offering the same 5-pin port on cell packs above 4 cells (i.e. 8 & 12 packs)?? Not that there's anything wrong with that, but the only way this is possible would depend on how the pack is wired internally. Being that our operational voltage is somewhere between 12-14v, there are only a limited combinations of series/parallel 3.3v cell wiring options (see attached).

    It's all about order. Given an array of cells, do you parallel cells 1st, and then follow in series (grid method). Or do you series the cells 1st into sub-packs, then parallel the sub-pack into a super-pack (series/parallel method). Either way will work, but the later will allow you to get wider BMS ports – hence greater access to all the cells. In grid wiring, there are interconnected cells in parallel, so the BMS pigtail wires really only access the group and not individual cells. Other complications such as current sharing, cell variance, and application of pack might warrant which wiring method is preferred .By now, you'll have noticed a reoccurring theme in regards to LFP batteries – and that is "individual access to cells". For me, I would prefer the wider BMS ports on higher number packs because I like the idea of being able to monitor/charge/control the state and health of each cell within the pack.

    I'd just like to add that there isn't a "wrong way" in pack design - rather a preferred way, or smart way. It comes down too, do I set myself up for failure or do I set my self up for success in regards to the life and longevity of my LFP battery pack. I'm not into vendor-bashing, I believe in the free market, and vendors (I won't name names) currently offering sub-par packs is okay, as long as that comes with a sub-par price, and the consumer is willing/wanting/understands it's a sub-par product. I am confident however, as the industry matures we will see better packs on the market with wider BMS ports, maybe standardizing the pin-out order, balance chargers by default, and finally built-in protective circuitry in the pack itself. But until that day comes, and if you're feeling confident, building your own pack as probably the best way to.


    [...continued...]
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    apriliaforum expert TimeBandit's Avatar
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    LFP's on motorcycles

    LFP's on motorcycles:
    Mainstream use of LFP's in bikes have been appearing mostly on the track, in the form of total-loss systems. After all, it's not hard to see the competitive advantage behind losing a 10 lbs hunk of lead battery, along with the stator and regulator/rectifier. Having several batteries on standby, balance-charged, and ready-to-go, quick-disconnects, swap and go is the name of the game. However, now we are seeing this battery type marketed to the everyday commuter / bike enthusiast, intended for primary battery usage, and having to contend with a charging system built around a forgiving lead-acid mindset.

    [see attached]

    Using a "protected" LFP pack as an example, I thought I'd illustrate how one might integrate it into a bike. The above diagram is from a Mille/Tuono wiring diagram, and the main concept being that we have isolated the starter leg wire off the main circuit. This way, when one hits the start button, the amps are pulled directly from the cell pack, and not through the PCM device - which may inadvertently trip it's Current safety. Since the bike's parasitic drains exist on the main circuit, we will want this connection moved to the PCM's (P+) protected terminal. This scenario allows the PCM to "disconnect" the battery from the bike in the event the pack voltage gets too low - thus saving the cells from subsequent damage. Something not illustrated, but perhaps viewed as a nice insurance feature, might be to install a momentary switch to bridge the (B+) and (P+) pack terminals at will. Logic in that, if ever the PCM electrically isolates the battery due to a typical under-voltage situation, that you still have the option (in an emergency) to start the bike up. In this respect, a PCM alone could help save you from ever being stranded on a completely dead battery.

    I'd say the most important points in this primer are 1) individual cell care, and 2) staying within the manufacturers prescribed safe cell voltage range. I could probably go into more depth, pro/cons, chemistry, etc... but I think this write-up is just enough to get your feet wet and consider yourself a little more LFP-wise. And, if you are one that already knows a thing or two about LFP technologies and want to contribute to this thread, please be my guest. A good consumer, is an informed consumer.

    [....end...]
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    apriliaforum expert potere's Avatar
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    great stuff!!

    thanks for putting this up
    potere - italian for power
    have M1 permit, will travel

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    apriliaforum expert ledwrist's Avatar
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    I'm curious where you got all this information. Do you have some links?

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    apriliaforum expert Prilliant03's Avatar
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    Quote Originally Posted by jonathan8940 View Post
    Interesting one. Keep it up.

    Pun intended


    Piss off spammer.
    "Life is like a sewer. You only get out of it what you put in."

    Tom Lehrer.

  8. #8
    apriliaforum expert TimeBandit's Avatar
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    Quote Originally Posted by ledwrist View Post
    I'm curious where you got all this information. Do you have some links?
    Awe shucks.... you got me - none of it is linkable - I made it all up. It's just a compilation of rumor, hearsay, and conjecture, and perhaps a sprinkle of imagination. BUT, I did sleep at a Holiday Inn last night!


    Sorry, sarcasm has gotten the better of me... it's just a "Primer" write-up, hence:

    "this is (I am) not the definitive guide on LFP packs. For that, it's best to conduct your own research and draw your own conclusions ."
    Best of luck.

  9. #9
    apriliaforum expert ledwrist's Avatar
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    You must be in sales, marketing or politics...

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    apriliaforum expert TimeBandit's Avatar
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    Quote Originally Posted by ledwrist View Post
    You must be in sales, marketing or politics...

    LOL - you forgot lawyers !

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    apriliaforum expert vweas's Avatar
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    ok how much?

    Ok you know what your talking about, I hardly have a clue! How much for the connecters protectors chargers! Is the only advantage to all this weight and positioning?





    Quote Originally Posted by dkw12002 View Post
    I admire people who can buy batteries, solder them together, add a controller and an electric motor and come up with a working bike that doesn't burn up. I own 3 e-bikes and a 2011 Zero S (from AF1), so I found the discussion interesting. The technology is almost there to start replacing gas cars and motorcycles, but right now most of us need gas-powered back-up.

  12. #12
    apriliaforum expert galloway840's Avatar
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    Not sure how I missed this, but nice write up and thanks for doing it!

    I'm an ME, not an EE, but you wrote it well enought that it was straight forward and easy to follow.

    Richard
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    1997 Yamaha TZ250 WERA Expert #246
    1984 Yamaha RZ350 undergoing restoration check it out at -
    http://www.rzrd500.com/phpBB2/viewtopic.php?t=3382

  13. #13
    Honest always, feared often Micah / AF1 Racing's Avatar
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    Just an FYI, I have been using a regular Battery Tender on both the bikes I store that have LiFe batteries, with excellent results thus far. Only 18 months into my personal experiment and so far both the Shorai and the Alien are doing kick ass. I do not leave either on the charger other than overnight once a month or so. No harm I can discern thus far.
    Diminished expectations is the key to happiness in life.

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  14. #14
    apriliaforum expert Matt fe2o3's Avatar
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    Micah, is AF1 selling the Shorai batteries?

  15. #15
    apriliaforum expert Bill in OKC's Avatar
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    I've had one in my Ducati for over two years now and a friend also has some experience with one. My experience is:
    Works for a long time as long as you keep them charged. Once they get low, low enough that it won't start your bike, a regular charger is not good enough to bring it back... which brings up the next bit: Some of these batteries (like the one my friend purchased) do not have balance charging capabilities ie: The ability to charge each cell individually instead of all at once. The companies that do not have this capability generally do not guarantee the battery if it has been deeply discharged. This is a shame because there is really nothing wrong with the battery - planned obsolescence maybe? RC enthusiasts use these exact same cells and routinely deep cycle them without problem. So - unless you keep them fully charged all the time - make sure you get a battery with the capability of balance charging the cells.
    '02 RSVR '07 S4Rs '08 FXSTB '75 GT550 '74 H1 500 '71 CB750

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