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PN what size 4S batteries are you talking about? 7 AH or what?
Just curious because I use a lot of them for RC planes.
Just curious because I use a lot of them for RC planes.
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MSEE, PE -
who is the big LiFiPo4 company now that A123 is OOB? All the cells in my 2 battery packs I use for raceing are A123 cells and I need to find another maker.1150W, Midnite Classic 200, Cotek PSW, 8 T-605sComment
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What size cells?
Tenergy, EVPST, HiPower Energy, and Forzatec make them. There are a lot of manufactures. Click Here for directory to all known manufactures.MSEE, PEComment
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Initially for me, these are anywhere from 2.5ah to about 13ah - real ah, and not the motorcycle marketing stuff like PBeq, or "lithium amp-hour". I only pay attention to either WH or true ah ratings. Not surprisingly, these cells are still designed for instantaneous power, and not capacity, however they were good enough for me to study the charge /discharge and other characteristics that assured me that it would be ok to get serious with much larger cells like CALB. I'd probably deal with calibpower out of Pomona CA directly.
The Shorai's make and impedance match their own prismatic cells. Others repackage A123 26650's into their own casings - which may or may not include balancing circuits. Witness the bms difference between EarthX (which does) and Antigravity (which doesn't).
I took a tip from the Antigravity folk who run with no bms, but use matched cells, and offerred up the Tecmate / Optimate TM-241 Lithium charger. It taught me that when a pack is under 12.8v rested ocv, then you don't want to apply a large amount of current until it reaches that point. If i had to do it manually, I'd do 0.1C until 12.8v was reached and continue on like normal - then again, I wouldn't discharge my cells down that far in the first place.
On the top end, since it isn't a true balance charger, it pulses the absorb between 14.0 and 14.4 somewhat slowly (enough for me to detect it with my Fluke) in an effort to burp the lower cells to life during that window of time before the cell with the highest voltage clamps down on current for the rest. It seems to work well, although I'm sure a dedicated bms could get things much more precise. For my application, I just don't need that kind of precision.
Of course, my wallet shed a tear when purchasing these things for study when a whole rack full of Trojan AGM's were just 3 feet away.
Still I had to press on and bite the bullet for science.
Took home a 2.5 year old Braille lifepo4 shelf-queen at a good price (made with A123 26650's internally) and it performs beautifully. With no way to do a balance charge individually, i just let the Optimate Lithium charger do it's thing. Full performance after the first charge.
Braille lithiums seems to offer up huge real ah capacity cells if you want them but of course these would be a poor $$ match for low-current applications (relatively), where high capacity CALB, Winston et al may be more appropriate.Comment
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To my knowledge, they are still in business but just have a different owner. They still have to supply these cells to the powersports industry after all. A123 stopped selling directly to experimenters a few years ago, but you can still get them from places like batteryspace.
The big question is are you putting together some random 4S pack that has not been capacity/ date / impedance matched? If so, you may be looking at living on a bms fulltime.
A West Mountain Radio CBA IV analyzer would make short work of capacity matching. Very cool is the ability to overlay previous test graphs from other cells over each other for analysis.
Whatever you do, make SURE you are not getting factory rejects, stolen goods, used or abused cells that may have been destined for recycling but laywayed somewhere else, or abused cells that have sat around in the low discharge knee (or worse reverse polarized, and subsequently carefully brought back to life) where a subsequent series of recharges leads to the commonly seen swelling and sometimes eventual pack rupture from dendrites. Reverse polarized cells brought back to life by shady techs and then sold this way are one thing to look out for. The 20ah prismatic pouches are very suspect unless purchased through a verified authorized dealer. Typically they have their tabs cut in half, missing the zipper fuses, old stock from Korea (they are no longer made there). Cells pulled from old Dewalt tool packs by DIY'ers don't count either.
And of course used cells that may appear ok are also subject to being lithium plated from exceeding the voltage limit from previous owners, with high internal resistance / bad pack balance / and other numerous ills as a result.
In other words, don't buy junk!Comment
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Don't forget Mr. Peukert vs Lifepo4
Re the proposed 100ah LiFeypo4 4S battery bank ....
While still insanely expensive, one other aspect that might also temper the initial purchase is comparing to how much it would cost for say an AGM replacement.
Example:
You intend to fully charge and use no more than 80% DOD of the 100ah lifepo4 bank. Basically you have 80ah available. With negligible peukert effect.
If you were to swap out your lifepo4 bank with a lead Pb bank, and due to the fact that we normally design our Pb systems to go no lower than 50% DOD, that means that a straight swap across would be to use 160ah of Pb.
BUT, toss in Mr. Peukert, and that replacement might in fact really need up to a 200ah Pb replacement.
Just something to think about when the wallet is crying out for some love.
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They are already together and I've been running them for 3 years ea. They are both 4S4P config and both are made from the A123 26550cells. The one I built myself is made from the drill battery cells with the paper covers, the one I bought is made from the green shrink film cells. The one I built does not have a balance circuit but it comes apart easily so once a year I just take it apart and charge the cells individually in a charger. The one I bought does have a balance charger circuit and I hook it up to my Turnigy charger about once a year as well but it is never very far at all out of balance, probably because it just isn't that many cells.1150W, Midnite Classic 200, Cotek PSW, 8 T-605sComment
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LiFePo4 4S battery bank: 12V 90AH battery packs
How much is "insanely expensive"?
What about these 12V batteries with 4 cells inside:
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I guess anything that costs more than double what a Pb Lead based battery would be over the top for most. Then again, when you factor in ALL the benefits, the price / performance ratio seems somewhat rational for enthusiasts.
I can't tell if those are from the major players like Winston, Sinopoly, CALB or the like. However, there is a good likelyhood that since they are already preconfigured as a 4S pack, they have been matched somewhat at the factory. Hopefully.
In fact, If I hadn't blown so much of my battery budget on these little powersports batteries for educational purposes, I'd being using something like that today.
The temptation would be immediately slap on a bms, but for me personally, I'd like to let my Fluke do the talking after monitoring how it goes for awhile.
Still, at those sizes, I like having the Tecmate / Optimate TM241 lithium charger on hand, just because it does more sanity checks other than just charging, albeit not being a true bms. At sizes larger than 50ah, I'd probably bulk charge these if at a very low SOC, and let the Optimate do it's thing to top them off.
Thastinger - even though you already have a nice individual cell balance charger for your 26650 pack, maybe consider the Optimate as a backup, primarily for it's automated testing and safe massive discharge recovery. Good to have a second opinion.
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Well PN and others I really admire your enthusiasm to experiment with Lithium batteries, and I am certain one of its variants will make breakthrough. With that said as it is today the economics just do not work with Renewable Energy and still quite a ways out. Electric Vehicles on the other hand are a different story because of the much higher Specific Energy Density, Low Internal Resistance, Deep Discharge Capability. But even today those characteristics are not good enough for the EV market.
On the Stand Alone Solar you just cannot justify the expense when you weigh all the parameters and look at end of life $/wh cost. Up front cost alone will cause your heart to miss a beat, but when you get to end of life $/wh cost it just gets nasty. To really look at the cost you have to make things measure up Apples to Apples. I will not go into all the details but by th etime you get to end of life cycle Lithium is on the order of 3 to 4 times higher than Pb. The only thing you gain using Lithium is they take up a less space and do not weigh as much both of which is not an issue in RE systems. Weight and volume is only important with EV's.MSEE, PEComment
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Re: the 100ah lifeypo4 4S bank again - personally I'd be tempted to make sure that if those bus bars are copper, and the terminal are aluminum, to put a very THIN coating of penetrox, noalox, aluminox or whatever goo there is available for joining dissimilar metals together. Don't manhandle the torque and wrench the heck out of the connectors either.
Onwards...
Don't forget powersports / racing vehicles. The common wisdom here is that one should stick to AGM if they are not willing to do their homework and stick in the largest lifepo4 that will fit especially if they have non-starting loads like heated gloves, crank tunes, computers and possibly parasitic loads.
I totally get what you are saying, but for those who don't do battery maintenance as a primary or secondary job, it is easy to burn through an expensive set of Pb batts and end up buying them all over again. Fortunately SolarPaneltalk can help many of us avoid that. Still, how many threads are there that face these Pb issues:
Sulfation
EQualization
Stratification
Specific Gravity
and so forth
With Lifepo4 and it's simple CV charging with only an HVC, and LVC, and possibly a bms if your application is >1C current draw, maintaining a life(y)po4 bank is easier to obtain something near the reputed cycle life.
Amazingly, my 2 1/2 year old Braille shelf-queen lifepo4 sat there and I found it near 40% DOD upon receipt. A single recharge and tracking on my CBA-IV found it having full stated capacity. Then again, there's no way for me to know if it will make 2000 cycles. But I'm working on it.
Different strokes for different folks - the additional characteristics beyond just weight and volume are important to me. It really simplifies things, but strangely, takes away the enjoyment I get out of doing normal Pb maintenance. I may move back just to create more work for myself.Comment
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PN all due respect charging is not quite as simple as CV. I agree it does use a CV technique but that implies a Float Charger, and you cannot float Lithium. They use constant current until they reach 4.1 to 4.2 vpc depending on chemistry, then switch to CV and terminate when charge current tapers down to 3 to 5% of C. If you leave them on CV it will destroy them.MSEE, PEComment
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And if you keep a Lithium battery at or near full charge, that will actually be worse for the service lifetime of the battery than keeping it at 2/3 charge or below.
SunnyBoy 3000 US, 18 BP Solar 175B panels.Comment
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Careful about those voltages - the ones mentioned (4.1 / 4.2) are LiCo02/ lithium cobalt, and not Lifepo4, which would be 3.65v per cell max.
Float is one thing I left off the list - see I forgot it already since it is unnecessary!
CV works just fine. Full charge for a 4S nominal 12v pack is 14.6v. At some point, you'll be sitting at the end of absorb (very quickly) with no appreciable current being drawn, unless you have passive or active circuits inline. Just pull the charge when there is no appreciable current is being drawn. This implies monitoring.
Consider that the Lifepo4 12v powersports batteries (both prismatic and cylindrical) do not RELY on anything but the CV charger in the vehicle. Some come with bms ports, but those are optional, and not mandatory. What happens to a fully charged lifepo4 battery on a vehicle that gets started and taken out for a 4 hour ride? Once the starting charge has been replenished, it just sits there at the regulated voltage, but no current is moving in the battery. This doesn't kill them.
Or better yet, reduce the HVC voltage to say 14.2v. That way, when the very slightly lengthened absorb is finished you are just sitting at 14.2v with no current. This accomplishes two things - more cycle life by not going to 100% all the time, and you are only sitting at 14.2v with no current. No lithium-plating. Note that I'm not suggesting you leave it like this forever.
It really isn't that complicated for our purposes. I hate to say it, but I think marketing forces want us to believe so for various reasons. I really wanted my lifepo4 setups to be ooooh so complicated and wizardly, but they are turning out to be great, but boring in the long run. Maybe that's a good thing.Comment
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