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LiFeYPo4 questions
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My Astron has both voltage and current limit controls on the face so I can charge about any battery I desire usin ga CV with current limit which is basically what any Lithium uses. FWIW RC batteries are LiPo, not cobalt. -
The fireproof bag is overkill for lifepo4 if taken care of properly. Lithium-Cobalt like in RC modeling - yes of course. Lacking a bag, for RC modelers using Li-Cobalt then perhaps use the fireplace at least. The enhanced safety from Lifepo4 comes at a cost - it has half the power-density of LiCo02, but now you don't have to use a bag or fireplace to charge them. Lifepo4 can actually be used where they need to be, unless one does the "lets destroy one up reeaal good in front of the firehouse" video for dramatic purposes.
I went to the source of the internal cells in my Braille, and got much more information. Seems like my target voltage of 14.2 was pretty close if I needed to do a faux-float as would be done if my batteries were charged up very quickly, and my solar charge controller just sat there at 14.2v for the rest of the day.
At the bottom you'll find the data sheets.
It incorporates an hvc, lvc, and internal bms. I am going to do all three manually on my Braille and Shorai's by merely limiting my charge voltage, discharge voltage, and perhaps use the Optimate TM-241 lithium charger as a faux-balancer once in a blue moon. Interesting is that they mention a float-voltage of 14.0, which implies that either they are planning on an external parasitic drain, say from an led or other circuit, or maybe they are implying that the internal bms itself is drawing a minute amount of power. The point is that the battery itself in bare form does not need a float, but constant parasitic external drains might make one want to incorporate that. Seems like they have no problem with them sitting at 14.0v, even though I won't be doing that in my solar application.
I do have Astrons and Daiwa power supplies - however again for lurkers - they need to be MODIFIED to be able to look into what appears to them as a direct short! The low-impedance of a lifepo4, agm, etc can make these throw their internal crowbar circuitry and worse if attached when the battery is at a low SOC. I'm also not going to dump more than 2C into these things, although I can, but for regular use a little Astron 4A - modified! - might do.
This is just making me jones out for getting my hands on some CALB or Winston large-capacity prismatics now. Nevertheless, I'm going to do this constant faux-float on my learner batts every time I charge and prove it to myself.Leave a comment:
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PN what you are doing is no real test using solar as the source of power. You do not get enough hours to do much damage. If you are a ham I bet you have something like a Astron DC supply. Crank it up to to 14.2 and put a 3S pack on it over night. Just be sure to put the battery into a fire/explosion proof bag they sell for charging RC batteries.
Bottom line chargers are made to be autonomous. I understand you can do what you do, but only if you are there to monitor things and terminate charge when you see current taper off. But 99% of the public do not have the time, skills, or knowledge to do that.Leave a comment:
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Tell ya what - I'll put my money where my mouth is.
My little Braille lifepo4 will be subjected to 14.2v extended charge from now on even when absorb is complete by at least 4 hours. This will simulate it becoming fully charged at the start of my typical solar insolation period. I'll report back. If it cuts the cycle life from 5K to 4.5K cycles, this might take awhile. With only 4 26650's inside, that is a mere 2.3Ah capacity so I should be able to run through those pretty quickly with my HF radio gear monitoring which is <1C current. This should be fun actually. I'll set my Xantrex pwm charger to 14.2v absorb AND float.
I can also force this with a Battery Tender charger designed for gel. It won't drop back to float once reaching the hvc and stays there until timeout. This is unlike my agm-specific Battery Tender which WILL reach 14.6v and once it senses about 100ma absorb, will drop back to float. So I'll use the gel model. I was going to throw these away, so thanks guys I found a new use for them.
Lurkers - ideally a charger should charge up to the HVC voltage and just stop, or better yet monitor the absorb current and stop at a low value, but these 1.25A BT's will drop back to a useless float voltage intended for Pb. Whatever you do, DO NOT use Schumacher speed-chargers, even if you set the chemistry / voltage correctly, as these units love to go to a high-voltage EQ charge, even if the voltage display says otherwise! Multimeters will reveal this behind the scenes helper which will destroy your lifepo4!Leave a 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.Leave a comment:
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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.Leave a 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.Leave a comment:
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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.Leave a comment:
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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.Leave a comment:
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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.Leave a comment:
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LiFePo4 4S battery bank: 12V 90AH battery packs
What about these 12V batteries with 4 cells inside:
tumblr_mnkydxnsmP1qa2swjo4_1280.jpgLeave a 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.Leave a comment:
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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!Leave a comment:
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