LiFeP04 Batteries for Solar & BMS

[PNjunction]

Heh, yeah as most 18650's are NOT lifepo4.

I'd suggest at least a 40ah battery made up of GBS, Winston, or CALBS.

On the low end, you could also put together 26550 LIFEPO4 Headways, popular with the DIY wheelchair crowd. Still, I'd just get smaller versions of the typical large-prismatic cells as they are closer in operating characteristics to what you'd use for a real solar bank anyway.

[Sunking]

In the meantime, have some fun and spring for a simple 12v 4S setup consisting of good quality GBS, CALB, or Winston cells.

Does not have to be that expensive or large, just some 18650 cells does the exact same thing. They don't leave as big as a hole in the ground when they explode

[PNjunction]

After lengthy discussion, if I build an off-grid SS, it will have a LFP bank bottom balanced, using quality CC and inverter/charger with programmable thresholds, and individual cell monitoring so I can assess health at a glance.

In the meantime, have some fun and spring for a simple 12v 4S setup consisting of good quality GBS, CALB, or Winston cells. I think you're ready, and the hands-on will provide reassurance that you can handle the larger setups. Try your hand at no-balancers, other than doing an initial sanity-check upon first charge, and stay out of the knees. Put a voltmeter on it once in awhile.

Mind - BLOWN.

[Living Large]

The whole idea of battery management is reducing the risks that operation will be outside the "safe area of operation".

This topic has been discussed at great length here. You can go back and read the threads. One user advises "take what you want and scrap the rest." That would be my advice. Every user's need and risk tolerance is somewhat unique.

After lengthy discussion, if I build an off-grid SS, it will have a LFP bank bottom balanced, using quality CC and inverter/charger with programmable thresholds, and individual cell monitoring so I can assess health at a glance. Stay on the flat part of the curve. Maybe additional disconnect if I think it needed, triggered by the cell level monitors. If someone else wants to do different, I say live and let live. Someone comes in here blasting away about top balancing vs bottom balancing at this point, and I remember the words "take what you want and scrap the rest."

[solar pete]

Thought I should pop into this thread for a look, so impressed that everyone seems to be arguing so nicely, cheers.

[PNjunction]

We can argue these points to death and have. I've moved on.

With my 40ah 12v 4S bank of GBS, I have also been able to succesfully TOP and BOTTOM balance (not at the same time mind you) a single dinky 20ah gbs cell into that 4S battery. Yep, that single 20ah cell will get hammered, and is of course the limiting factor overall.

Thing is, nobody would run a battery made like that with a single cell half the capacity of the other three, and just proves a point about balance being a total misnomer based on voltage.

So real world - aside from doing an initial sanity check upon first charge for a reasonable balance, there is no need to go bananas over minute differences which are going to change anyway as the cells age. That is, if you are buying quality, and not some e-bike online used trash held together with duct tape. THAT mandates a balancer band-aid to protect and disguise the horrid quality.

In addition, what everyone seems to forget - but Sunking points out too, is that *in our application*, that is a so-called "Sub-C" low-current environment of a solar housebank, or even a small solar project designed correctly, the differences won't be aggravated like they would be in EV use.

Your gear will start failing long before you reach bottom anyway. And, you may not even have enough solar insolation to trigger the bleeder-boards long enough at the top, which all of us agree are a point-of-failure waiting to happen - again in this sub-c environment of usually no more than about .1 to maybe .2C.

Unless someone designs their solar system for absolutely no autonomy, and desires to discharge to 80% DOD daily, the bank is too small. Designed properly, a solar housebank or even a smaller project should have a battery that will most likely never see anything higher about 95% SOC, and anything below than about 60% DOD.

So for the most part, any cyclic solar user will probably always be in a psoc environment, with low currents, in the flat part of the curve, and one may never encounter any slight aging or manufacturing issues that would crop up like it would with EV. Not that I endorse low quality, but I'm just saying that if we don't get things absolutely lab-perfect, we still may never see issues if we've done our autonomy and power budget correctly in the first place.

I'm not advocating a totally hands-off approach either. Some form of monitoring on a regular basis should take place. If one is buying trash, then you better have insurance. If you buy good quality, and use the cells in our "Sub-C" application, then I'm comfortable with reasonable levels of monitoring.

Someday we may be able to move beyond the obsession with either top or bottom balancing, and really discover the additional freedoms that come with lifepo4 in a solar cyclic scenario. Unfortunately, we always get sidetracked by non-solar issues.

[Jerry Liebler]

Incorrect statement. Capacity is determined by the weakest cell, not cycle life as you hav e indicated is completely false.

Cell life is a function of depth of the cycles and the number of cycles. The cell being cycled over more of it's capacity WILL have a shorter life span. I'll accept your apology!

Another incorrect assumption. Cells do not drift unless you use cell monitor and other parasitic loads. When in series and BB, all cells have the eexact same capacity at any SOC level.

ONLY if they are at the same temperature and have identical parasitic leakage.
I'll agree cell drift is a minor concern but it is measurable and real.

BB balance requires absolutely NO Cell Level Monitoring at discharge. All the cells reach 2.5 volts at the same time. Actually they all reach 3 volts at the exact same time, but 2.5 volts is what you want to say at or above. On a 4S or 12 volt pack, you set your Inverter at 12 volt Low Voltage Disconnect or 3 vpc a full 2 volt above 10 volt do not go below. You can drive a truck through a 2 volt window blindfolded. Once your cells reach 2,5 vpc, no adjacent cell can possibly discharge through another 2.5 vpc. There is no energy left, only voltage. That makes it impossible to over discharge a BB pack. One can very easily over discharge a TB pack.

You can make the argument that pack voltage is sufficient at the "balanced" end, if they are still balanced, but must admit that per cell measurement is required at the other end, at least once!
Depending on pack voltage at BOTH extremes invites disaster no matter how the cells were balanced.

IF as you seem to believe LIFEPO4 cells never change, the only benefit of ANY attempt at balancing is increased capacity and operation between 2 pack voltage limits, once characterized by per cell measurements, will work forever.

Like it or not even these cells suffer many forms of degradation and change many characteristics. The whole idea of battery management is reducing the risks that operation will be outside the "safe area of operation".

Many so called BMS are actually battery murdering systems because of the parasitic load they place on the cells. These loads often vary wildly from cell to cell making the situation worse. Well designed BMS hardware is very cost effective assurance of good cell life and almost all such hardware uses top balancing with shunts and per cell low voltage limits.

[Sunking]

The ONLY advantage of bottom balancing is that the better cells are not charged as fully and therefore have a longer life (but pack life is determined by that weakest cell).

Incorrect statement. Capacity is determined by the weakest cell, not cycle life as you hav e indicated is completely false.

The real advantage of top balancing, as typically implemented, by using voltage controlled shunts, is that it is "refreshed" with every charge cycle and thus eliminates any drift which would go unmitigated with a bottom balanced pack.

Another incorrect assumption. Cells do not drift unless you use cell monitor and other parasitic loads. When in series and BB, all cells have the eexact same capacity at any SOC level.

With either method a per cell monitoring is vital to discharge termination. With bottom balancing per cell monitoring MUST (at least once) be used for charge termination while with top balance and "voltage controlled shunts" pack voltage can safely be used for charge termination.

BB balance requires absolutely NO Cell Level Monitoring at discharge. All the cells reach 2.5 volts at the same time. Actually they all reach 3 volts at the exact same time, but 2.5 volts is what you want to say at or above. On a 4S or 12 volt pack, you set your Inverter at 12 volt Low Voltage Disconnect or 3 vpc a full 2 volt above 10 volt do not go below. You can drive a truck through a 2 volt window blindfolded. Once your cells reach 2,5 vpc, no adjacent cell can possibly discharge through another 2.5 vpc. There is no energy left, only voltage. That makes it impossible to over discharge a BB pack. One can very easily over discharge a TB pack.

[Jerry Liebler]

Why I prefer top banancing!

With either top balancing or bottom balancing, the weakest cell goes through EXACTLY the same cycle! The ONLY advantage of bottom balancing is that the better cells are not charged as fully and therefore have a longer life (but pack life is determined by that weakest cell). The real advantage of top balancing, as typically implemented, by using voltage controlled shunts, is that it is "refreshed" with every charge cycle and thus eliminates any drift which would go unmitigated with a bottom balanced pack. With either method a per cell monitoring is vital to discharge termination. With bottom balancing per cell monitoring MUST (at least once) be used for charge termination while with top balance and "voltage controlled shunts" pack voltage can safely be used for charge termination.

[Living Large]

Manufactures do not sell used underwear.

I'd like to comment on this, but I won't. It would be off-topic...

[Sunking]

You can bet that some looked at this for a historical template to restrict us all, manufacturers alike, to the small-cylindrical format, adding complexity, limiting choices, and basically a lock-down. I guess that STILL bugs me to this day:

https://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries

Ok, enough of my own weird tangent I suppose.

Yeah I followed that too but never bought into the Conspiracy thing. If you look back it just does not add up. What I see is sour grapes being eaten by Dr O****ani. He sold his patent and surrendered his rights. Kind of like Nickoli Tesla selling all his patents to Westinghouse and JP Morgan. Brilliant Scientist, lousy businessman. You cannot blame GM, Chevron, and Texaco for wanting a lock on NiMh batteries anymore than you can blame Gates for a lock on PC's. It is just biz. At the time GM thought EV's would be powered by NiMh and they wanted a piece of the action. They lost the bet and their investment. Chit happens. What killed the EV was the market and lacking technology, not GM. Same thing today.

[PNjunction]

At the consumer level and DIY all there really is to chose from is Chi-Com LFP cells. You know the history there too, all from failed Thundersky comes CALB, GBS, Sinopoly, etc. All are on 3rd generation revisions in 8 short years because the first two are flops. Non could meet the claims, and time will tell if gen 3 can live up to the claims today which does not look good. Now there are some commercial offerings, some are not real like Powerwall, and others that you can buy in foreign markets. But the price of using high quality cells in a manufactured solution still cannot compete with PB technologies, and life cycle question cannot be answered for another 10 years.

I can dig that, but for the reader, "failed" or bankrupt in the business world does not mean out for the count. Restructure, reorganize, IMPROVE the product. Don't forget that many of these early failures from the pioneers in lifepo4 prismatic EV were from total abuse, homebrew vampire balancers, - crappy wiring infrastructure, the whole plethora of badness from an amateur construction standpoint. They don't have the knowledge we do now.

I watched the same details more or less when every EV'er was lugging around Enersys (Genesis) agm's, Optima, Hawker, later Odysseys and their failures from many of the same issues! But back then, we didn't have the 'net in the state it is in now. I wonder if ANY high-end agm manufacturer could survive if the only reports we get from the field are from the guys who blew the tops off their systems with hydrogen explosions and everyone jumping on board to claim that agm's tech is bad, when it was the homebrew balancing boards (yes, they had them then too!) that threw the systems totally out of whack. That pesky mist!

For now cheap Chi_Com knock-offs is all we got.

Thank goodness for that! Every advancement since just plain old flooded seems destined for a total proprietary lock-in or patent-war fodder where the benefits to mankind are locked away or delayed forever. (Nimh patent encumbrance forcing us to a 10ah cell limitation, and so forth as just one old example). At least the common-man can get hold of the prismatics relatively easily, whose sizes allow us to abide by the KISS principle when doing something larger than just gadgetry.

You can bet that some looked at this for a historical template to restrict us all, manufacturers alike, to the small-cylindrical format, adding complexity, limiting choices, and basically a lock-down. I guess that STILL bugs me to this day:

https://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries

Ok, enough of my own weird tangent I suppose.

[Sunking]

PN I know I am not telling you anything you already do not know. The demand from auto, laptop, power tool, and gizmo's manufactures consumes all the battery manufactures production. At least the better ones like Panasonic, EnerDel, and LG Chem. For Pete's sake that is what has opened up the door for Tesla to build Panasonic cells in the USA when they complete phase one and two of the so called Gigafactory. Even Tesla has problems with dried up supplies. Even A123 Systems, what is left of it, production is is consumed by GM, Daimler and a handful of other EV manufactures.

At the consumer level and DIY all there really is to chose from is Chi-Com LFP cells. You know the history there too, all from failed Thundersky comes CALB, GBS, Sinopoly, etc. All are on 3rd generation revisions in 8 short years because the first two are flops. Non could meet the claims, and time will tell if gen 3 can live up to the claims today which does not look good. Now there are some commercial offerings, some are not real like Powerwall, and others that you can buy in foreign markets. But the price of using high quality cells in a manufactured solution still cannot compete with PB technologies, and life cycle question cannot be answered for another 10 years.

I understand people want to eat the forbidden fruit of real EV batteries. But unless you are willing to pay huge money for the high quality lithium batteries. that cannot compete with long term cost of Pb, we are still a long ways off from lithium as power storage. It will come to the commercial market long before it arrives at the consume level. I do not see that happening anytime soon as production cannot even handle EV production today. Long way off from meeting the demand of EV, utility scale energy storage and consumer. Not even Tesla factory will change that.

For now cheap Chi_Com knock-offs is all we got. I was really disappointed Lithium Titanate clss realy never caught on for Energy storage. Those have the best chance of 5000 to 10,000 cycles. But Specific Energy Density is not much better than Pb, and right now it is EV's driving the technology and low Energy Density is not going to make it in any market. All but home solar demands high energy density, and there is no real market for a battery manufacture to make lithium cells for home energy. The money is in EV's, power tools, and gizmos.

[PNjunction]

PN supply is the driving factor. Stop and think about it for a second PN. You already know one thing, may net be aware of it, but you and I cannot buy EV quality lithium batteries. Not th eones Ev manufactures use. Hell 8 years ago not even Tesla could access the batteries they needed. They gambled on LiCo laptop 18650 cells about the size of a AA battery made by Panasonic.

In another life-form, I love my recent Panasonic-built 18650 LiNMc's, but that is a totally different application.

Ah but the point here is that we don't *need* that kind of quality and capability for a solar bank sized appropriately for autonomy! The large prismatics from the established majors (GBS, CALB, Winston) are already quite a bit beyond our relatively low current needs. Unless one is charging with a genny, they are merely tickling the capabilities of these things. From a financial standpoint, the costlier small cylindricals are even worse since one will never use their 10C or more capability.

There is always the manufacturing quality issue - but if we take it to say the Pb realm, does everyone really need a Rolls or Trojan for their application? (retorical, other threads cover this!

The scary part is LiCo, LiPo, LFP, and th elist goes on is just alphabet soup to the public. All they know is a Lithium Battery. We know the public cannot buy quality Lithium batteries at competitive prices. Tool. gadget, and auto makes have all the good ones tied up in production.

I would say that the large prismatics available today *for our solar purposes* are good enough. Maybe not like Rolls or Trojan Pb builds for sure. Guys don't need to install an Enersys power-vault of high end agm's for every purpose either. Stopping here so I don't go off on pb issues..

While considering the needs of the general public is admirable, not knowing about lithium is not surprising considering that most don't know the difference in Pb batteries either - and that is 100 year old tech basically. So we aren't really in a manufacturer-mindset, but educators for those that WANT to know and come for guidance. Guidance, not salesmanship.

I'm just sort of dismayed that all roads (here and elsewhere) quickly lead back to Tesla, Fiskar, Boeing, E-bikes, EV, hacks, corporate politics, CFO's and other motive-power needs, when just the basics of lifepo4 for the guy interested to doing it with solar ends up buried in the noise. For many, finding the details you need to get started even just for personal experimentation becomes a non-starter.

Guess what - I needed a new backup system. Lifepo4 (or any other lithium) wasn't part of that plan. See ya in another thread about that!

[Sunking]

The litmus-test for me always has been availability to the common man, under NORMAL means of business without having to hack anything. There are hacking forums for the hacking crowd. Not all of them are safety-unaware, but because kids don't see lifepo4 at their local auto store, they may assume that getting damaged goods is how it is done.

PN supply is the driving factor. Stop and think about it for a second PN. You already know one thing, may net be aware of it, but you and I cannot buy EV quality lithium batteries. Not th eones Ev manufactures use. Hell 8 years ago not even Tesla could access the batteries they needed. They gambled on LiCo laptop 18650 cells about the size of a AA battery made by Panasonic.

A123 came out with the Holly Grail th eLFP battery and it flopped. It lacked density and price point. That left the Chi-Coms LFP to the public domain. The scary part is LiCo, LiPo, LFP, and th elist goes on is just alphabet soup to the public. All they know is a Lithium Battery. We know the public cannot buy quality Lithium batteries at competitive prices. Tool. gadget, and auto makes have all the good ones tied up in production.