LiFePo vs Lead Acid - Knowledge and myths

[parmm]

I don't believe all LiFePO4 batteries have a BMS system and I don't believe one is needed. But, just like lead acid batteries, you best pay attention to what your batteries are doing and how your are charging them!!! I know mine have a BMS, and even a heating system. Would not leave home without it. I killed way to many lead acid and AGM batteries!



BMS facts and how to charge lifepo4 without it:

https://endless-sphere.com/forums/viewtopic.php?t=15757

[sokhapkin]

Originally Posted by parmm

I don't believe all LiFePO4 batteries have a BMS system and I don't believe one is needed.

Cound you provide a few examples of LFP batteries without BMS sold today? I don't believe such dinosaurs even exist nowdays.

[jwcolby123]

Originally Posted by parmm

I don't believe all LiFePO4 batteries have a BMS system and I don't believe one is needed. But, just like lead acid batteries, you best pay attention to what your batteries are doing and how your are charging them!!! I know mine have a BMS, and even a heating system. Would not leave home without it. I killed way to many lead acid and AGM batteries!

BMS facts and how to charge lifepo4 without it:

https://endless-sphere.com/forums/viewtopic.php?t=15757

Good advice all the way around. A BMS is just a good investment for an even better investment, a LiFePO4 battery. And yes, most assembled batteries already have them.

It turns out that you can often use the charger itself to cut off at a specific voltage. Set that voltage to 3.4v /cell - 13.6v at the battery level and you won't over-charge. Then jusyt don't discharge all the way down, that will still be on you.

With that out of the way, the BMS just handles the details and lets me get back to having fun instead of being a BMS.

[jwcolby123]

As a YouTube speaker I was watching said, "The charge capacity of a Lithium battery depends entirely on the amount of Lithium in the battery."

I watched a YouTube video of a LiFePO4 battery assembly line. The process involved spraying a Lithium Iron solution, called a deposition layer, onto a 6 foot wide roll of Aluminum foil. It is then dried, and slit into strips. Those strips are rolled around a core, or folded to make pouch cells. At that point an acid solution is injected / vacuumed into the cell between the foil layers. That construct is then encased in something, a metal shell etc and a cell is formed.

From this discussion it should be obvious that every cell is just a little different. Perhaps the deposition layer is not quite uniform, or the strip is a thousandth of an inch wider than another battery. Anyone who has researched Lithium batteries knows, the batteries are quoted as "X kilos +/-. Also something like 105 ah +/-.

The +/- is in part due to the very slight differences in construction from cell to cell. "Manufacturing variations".

In addition to this difference in Lithium contained (and thus charge capacity), each cell has an "Internal resistance". While a battery internal resistance is not a true resistance like found in your normal electronics resistors, it is a "chemical resistance" to charge and discharge which causes internal heating and other "losses" (chemical resistances to ions moving around mostly).

It may be helpful to know that at least in a LiFePO4 battery, electrons flow out of the battery, at some "close to light" speed, but when that happens it causes a charge which forces the Ion (a molecule missing an electron) to physically move as well. However the ion cannot move even close to light speed, it is physically moving through an electrolyte solution.

In a LiFePO4 battery, these ions move into and out of that deposition layer I discussed earlier. At first the ions collect on or near the surface of that layer, but as the available spaces capable of holding an ion fill up, ions have to burrow down into the material which takes more force, as well as more time. Force / time = heat. The more force (voltage) or less time (more rapid charge / discharge) causes heat. Or more correctly more heat at once. And high heat is damaging to the battery.

An 'oh btw', any given electron only really move a very very short distance, as in micrometers, or a few atoms. They don't pop out of a battery on one end and back into the battery on the other end, although another 'replacement' electron does in fact pop into the other side.

The point is that the cells of a battery, there are 4 cells for a 12v battery, are all slightly different, both in charge capacity and 'resistance'. It is these differences that make up the 'unbalance' that you see between cells of a battery.

As current flows out of the battery as a whole, each cell supplies essentially the same amount of current. However each cell is slightly different in how much current it actually holds. Thus the cell with the smallest charge capacity 'runs out' of current first. As cells charge and discharge, their voltage increases (charge) or decreases (discharge). For a LiFePO4 battery (and every chemistry is different) the maximum charge voltage is 3.65v and the minimum charge voltage is 2.5v.

As discussed previously, the job of the BMS is to stop the entire battery charge or discharge process as the "weakest" cell either hits its max voltage or its min voltage. Let's say that cell one has 102.5 ah of capacity but cell two has 103 ah of capacity (and the other cells vary as well). When the battery discharges 102 ah of current, the voltage is dropping on all of the cells, but because the "weakest" cell gives up all of its current first, it hits 2.5v first. The BMS correctly turns off discharging the battery. Cell 2 still contains .5ah of capacity but it is unable to provide that current to the load because cell one would be damaged if the battery as a whole continued to discharge. So the BMS disconnects the battery from the load, stopping the discharge.

That is one aspect of 'unbalanced' cells.

Another aspect is that "resistance" we discussed earlier. If cell 1 has a resistance higher than cell two, then cell one will dissipate more of its current as heat, thus reducing the current actually available at the terminals. But if X ah has to be delivered, then in the end, the cell with the higher resistance will end up discharged faster because more of its available charge is wasted as heat.

There are probably other problems as well but these two are already contributing to the individual cells ending up discharged at different times, which causes the battery to be unbalanced.

The big questions are how fast and does it even matter?

How fast just depends on the individual cells. The manufacturers are supposed to test each cell and then select cells that have very similar capacity and internal resistance to form the bigger battery. It doesn't really matter what the resistances or capacities of the four cells are as long as they are the same. If they are the same, then the drift will be very slow and gradual, 'the same' cannot be truly identical after all.

Does it matter? That depends pretty much entirely on whether you need to get all the power out of the battery. Let's assume that you buy a 4 cell 12v battery with a rated capacity of 100ah. Let's further assume that the cells are horribly matched and over three months the battery loses a full ah of its rated capacity due to these issues discussed above.

Now lets assume that you only ever use 75ah, 80ah, 47 ah, 52 ah etc etc.

Will you notice that your 100ah battery is only providing 99 ah? OTOH if you simply do not have sufficient capacity for your usage and every single night you use every single ah... then you will eventually notice that your battery is creeping downwards in capacity. At which point, you take the time and effort to allow or even force the battery to 'balance'.

So there you know what I know about cell balancing, unbalancing and the state of the world as it relates to LiFePO4 batteries.

[AlanKilian]

Originally Posted by jwcolby123

It turns out that you can often use the charger itself to cut off at a specific voltage. Set that voltage to 3.4v /cell - 13.6v at the battery level and you won't over-charge..

I'm not sure how your spell checker modified your post, but I'm pretty sure you meant that if you set a (non-balance) charger at 3.4 Volts-per-cell and charge a battery pack without a BMS that you are GUARANTEED to overcharge a cell in the pack.

After a few discharge/charge cycles, one of the cells will obviously have slightly less capacity and will hit a higher cell-voltage than the others.

After several cycles, when three of your cells are at 3.2 Volts because they have slightly more capacity than the weak one, the weak one will be at 4.0 Volts which is significantly above the maximum safe voltage for an individual cell.

I understand your position, but even hinting that RV people can run a pack without a BMS is simply irresponsible in my opinion.

I get that YOU are an expert, but don't assume others are.
(HEY??? Isn't that what you complain about in this thread about others???)

[ThomasC]

Originally Posted by sokhapkin

Cound you provide a few examples of LFP batteries without BMS sold today? I don't believe such dinosaurs even exist nowdays.

Victron has batteries without a BMS. https://www.victronenergy.com/batter...-battery-12-8v

It also has a battery with a BMS. https://www.victronenergy.com/batter...hium-superpack

[CarlD]

An LFP battery system without a BMS, is something you do not want, unless of course you like playing with batteries more than camping. A BMS should also include a cell balancing capability, low and high temperature cutoffs and low and high voltage cutoffs. Just so you know, charging a lithium battery below freezing temperatures at high rates causes lithium plating of the anode instead of integrating the lithium back into the anode structure. This plating is not smooth but forms dendrites, little spike structures, which can grow across the membrane and short out the cell. This can cause a fire.

LFP batteries have their issues just like lead acid batteries (lead acid batteries can explode), however there are ways to make them easy to use and safe for the masses. So when looking to purchase a LFP battery system, base your search on Battleborn LFP battery specifications which are all inclusive.

[jwcolby123]

Originally Posted by AlanKilian

I'm not sure how your spell checker modified your post, but I'm pretty sure you meant that if you set a (non-balance) charger at 3.4 Volts-per-cell and charge a battery pack without a BMS that you are GUARANTEED to overcharge a cell in the pack.

After a few discharge/charge cycles, one of the cells will obviously have slightly less capacity and will hit a higher cell-voltage than the others.

After several cycles, when three of your cells are at 3.2 Volts because they have slightly more capacity than the weak one, the weak one will be at 4.0 Volts which is significantly above the maximum safe voltage for an individual cell.

I understand your position, but even hinting that RV people can run a pack without a BMS is simply irresponsible in my opinion.

I get that YOU are an expert, but don't assume others are.
(HEY??? Isn't that what you complain about in this thread about others???)

Well, do it and come back and tell me how it does that. Yes, if you start with one cell dead and all the rest charged you are going to kill a cell, in just one charge cycle.. OTOH if you are operating without a BMS you are, in the words of one of our diehard Lead Acid guys, "your battery's bms".

You are expected to know about placing every cell in parallel and letting them balance between themselves. You are expected to test the cells for capacity. You are not going to place a 100ah cell and a 280ah cell together in series and try to get 280 ah out of the results.

No, I do not and have never suggested running LiFePO4 without a BMS, however comma, the whole "unbalanced" thing is way overrated. It really is a very slow process. And if you want to be your battery's BMS it is possible to do so, just as it is with a Lead Acid battery.

Think about Battle Born. The take a dozen cells and place them in parallel. Do you think those individual cells aren't getting out of balance? They test them, they select them to be as closely alike as they can, then they throw them in parallel and off they go. And yes, sometime out in the far far future one will be very badly out of balance with the rest. But it will not be "After a few discharge/charge cycles".

Go back and read the in-depth post about how and why unbalancing even occurs at all. Then I urge you to get some cells and actually experiment, charging and discharging and watch the individual cells. I have done so. The process is pretty darned slow.

And what I complain about is folks coming in to a thread and giving flip answers such as "Yea, you'll be fine". I can not see any circumstance where an answer like that is even useful, and for a nubee will be totally dangerous. I have spent literally hours providing very in depth information about this subject, Trying very hard to give very complete answers that will help the nubee come up to speed. I pray to My God that I have never left an OP with "yea you'll be fine" as my total answer.

[zack sc]

I am finding this really convincing. Where I mostly live and camp, in central coastal California, the temperature swings are not that great and I’m thinking I could get away with non-heated batteries here. From what I read above there are some really good prices on those right now. Do you think I would be missing out on some special bargains if I don’t act soon, Or is it OK to wait another six months or so before I switch over to lithium batteries?

[gordon2]

Originally Posted by zack sc

... Do you think I would be missing out on some special bargains if I don’t act soon, Or is it OK to wait another six months or so before I switch over to lithium batteries?

I wondered about that myself.. and while I have no inside knowledge, I do think that prices will continue to drop, and in 9-12 months maybe be 2 -3 times the price of cheap lead acid batteries for comparable amount of usable watt hours.

[parmm]

Originally Posted by gordon2

I wondered about that myself.. and while I have no inside knowledge, I do think that prices will continue to drop, and in 9-12 months maybe be 2 -3 times the price of cheap lead acid batteries for comparable amount of usable watt hours.

That all depends on what countries we get the raw materials from and our trade issues with them. "With 8 million tons, Chile has the world’s largest known lithium reserves. This puts the South American country ahead of Australia (2.7 million tons), Argentina (2 million tons) and China (1 million tons). Within Europe, Portugal has smaller quantities of the valuable raw material. The total global reserves are estimated at 14 million tons. This corresponds to 165 times the production volume in 2018."

[CarlD]

Originally Posted by gordon2

I wondered about that myself.. and while I have no inside knowledge, I do think that prices will continue to drop, and in 9-12 months maybe be 2 -3 times the price of cheap lead acid batteries for comparable amount of usable watt hours.

Battery powered vehicles are becoming more popular every day. The big boys, GM, Ford, etc. are all moving quite quickly in that direction. As they become more popular battery production will increase. Costs will drop as volume increases. They all currently use lithium based batteries.

Lithium is widely available and mining will be able to keep up with demand. As demand increases mining techniques will evolve to reduce costs.

Lithium recycling is not currently very efficient at the moment, however engineering will figure out how to do it.

I firmly believe lithium battery technologies will follow the usual technology life cycle. High cost to lower cost, volume increase as the technology becomes more wide spread, then replaced by something new.

Looking on the interweb you find ever more sources for LFP battery systems (battery plus internal and external BMS combinations) at ever lower prices.

It looks like we are at the beginning of a lithium battery explosion and I think prices will fall as we move forward.

It seems to me that prices will continue drop over the next few years, so I don't think it would hurt to wait to purchase.

[jwcolby123]

Originally Posted by zack sc

I am finding this really convincing. Where I mostly live and camp, in central coastal California, the temperature swings are not that great and I’m thinking I could get away with non-heated batteries here. From what I read above there are some really good prices on those right now. Do you think I would be missing out on some special bargains if I don’t act soon, Or is it OK to wait another six months or so before I switch over to lithium batteries?

Like the others I think prices are dropping, somewhat quickly. I haven't found any particular bargains right now, in fact short term, prices seem pretty stable.

But there are many ways to get in the game. If you want to convert a camper (you didn't say, but I assume) then just go get a good quality mass market device such as the Chins/AmpereHour 100ah battery, pull your PbA and drop the new battery in.

OTOH the so called 'Solar Generators' such as Bluetti can make a pretty convincing argument for your dollars. The battery and all the fixins in one box. And taken together the cost is right in line with what you would pay for putting a similar system together from the pieces. Plus they are usually solar ready. Just be aware that the older models sometimes use the older Lithium Ion batteries rather than the LiFePO4 chemistry.

Or you can build your own 'Solar Generator'. Lots of YouTube videos on making one in a milk crate etc. Doing that would give you a stellar working knowledge on how it all plays together.

To your original question, no harm in waiting until your Lead Acid dies. It almost certainly will in the not too distant future. JMOOC.

[chrisblessing]

Originally Posted by zack sc

I am finding this really convincing. Where I mostly live and camp, in central coastal California, the temperature swings are not that great and I’m thinking I could get away with non-heated batteries here. From what I read above there are some really good prices on those right now. Do you think I would be missing out on some special bargains if I don’t act soon, Or is it OK to wait another six months or so before I switch over to lithium batteries?

I would wait. The shipping times from China can be as long as 3 months. Perhaps by 2022 you'll find good deals as well as reasonable shipping times.

[Defenestrator]

Originally Posted by jwcolby123

Think about Battle Born. The take a dozen cells and place them in parallel. Do you think those individual cells aren't getting out of balance? They test them, they select them to be as closely alike as they can, then they throw them in parallel and off they go. And yes, sometime out in the far far future one will be very badly out of balance with the rest. But it will not be "After a few discharge/charge cycles".

How would they get out of balance if they're in parallel? They might have varying charge capacities, but they'll end up at the exact same voltage pretty quickly. At most they might diverge briefly under rapid charge or discharge.

[CarlD]

Originally Posted by Defenestrator

How would they get out of balance if they're in parallel? They might have varying charge capacities, but they'll end up at the exact same voltage pretty quickly. At most they might diverge briefly under rapid charge or discharge.

If you look at the internal configuration of a 12 volt LFP it is comprised of 4 groups of parallel strings connected in series or 4 giant cells connected in series. It is not the parallel cells that get out of balance relative to each other because they all have the same voltage. They act as one really large cell. It is the parallel connected groups relative to each other that get out of balance.The cells are connect this way so the BMS only needs 4 balance circuits. If it were the other way around (many parallel groups of 4 cells in series) you would need a balance circuit for each series string which is much more complex and costly.

[jwcolby123]

Originally Posted by Defenestrator

How would they get out of balance if they're in parallel? They might have varying charge capacities, but they'll end up at the exact same voltage pretty quickly. At most they might diverge briefly under rapid charge or discharge.

To make an illustration, assume that you put a 10ah cell and an 11ah cell in parallel. Let them sit to equalize. Now start charging them to full (3.65v). One cell will completely charge and want to shut off the charger because it is full, but the other cell is not full and it is not yet in its knee. These two cells are "out of balance".

The larger cell is still consuming current, and holds the voltage at it's charge state voltage (let's say 3.5v). The smaller cell is already full, and would normally put out 3.65v but it can't, so the charger (BMS) continues to feed current to the parallel pair because it is designed to put 3.65v into the cell and will do so until all of the cells are full and so the charge current drops. But the smaller capacity cell is 'out of balance' with the larger cell and, while it is completely charged, it continues to be charged (overcharged) because it cannot independently flex it's knee and display its normal 3.65 voltage which would otherwise tell the bms to stop charging.

Obviously the numbers in a Battle Born won't be this extreme but capacity differences will exist. The way out of this is to hold the max charge voltage well below 3.65v, let's say 3.5v. This allows smaller cells with minor capacity differences to fill up faster and yet the charging will shut down in time to prevent damage.

Battle Born does cut off discharge well above the otherwise normal 2.5v for exactly this reason, but it is not clear that they shut down charging early.

[jwcolby123]

Originally Posted by CarlD

If you look at the internal configuration of a 12 volt LFP it is comprised of 4 groups of parallel strings connected in series or 4 giant cells connected in series. It is not the parallel cells that get out of balance relative to each other because they all have the same voltage. They act as one really large cell. It is the parallel connected groups relative to each other that get out of balance.The cells are connect this way so the BMS only needs 4 balance circuits. If it were the other way around (many parallel groups of 4 cells in series) you would need a balance circuit for each series string which is much more complex and costly.

In fact both scenarios can occur. The problem is that the bms cannot "see" out of balance parallel cells.

[jwcolby123]

https://www.instructables.com/DIY-1k...ge-Controller/

Looks promising. I'm thinking about building one. Or maybe a couple.

[AlanKilian]

Originally Posted by jwcolby123

https://www.instructables.com/DIY-1k...ge-Controller/

Looks promising. I'm thinking about building one. Or maybe a couple.

That is one INCREDIBLE Instructable project.
It's the template for how projects like this should be documented.

Thanks for pointing it out.

(The build vs. buy equation says "Buy" for me, but our lives are probably pretty different.)