LiFePO4 - The future for off-grid battery banks?

[karrak]

He stated several advantages to using large format. I still don't recall him saying only large format should be used - but honestly, I don't see why it matters and I'm not paging through comments to hyper-analyze what each person said. This has gotten quite absurd.

As an engineer you should know that the devil is usually in the detail. It does matter.

I can think of three reasons why smaller 20-50Ah cells in metal cases might be better than large cells in plastic cases. These reasons have been alluded to by dax who I would think knows far more than me. They are:

1. Thermal Management: Large cells, especially if they are thick and have an insulating cover will be hotter in the middle of the cell than on the edges when charging or discharging, the heat being generated by the resistive losses in the cell . It will also be harder to dissipate this heat evenly. This will mean that the middle of the cell will degrade faster than the edges. This is not so much of a problem with low charge and discharge rates, but I am sure will still be a factor.
2. Mechanical Stability: These cells are made up of vast numbers of microscopic particles each acting almost like an individual cell. For each of these particles to add to the total they must be in continuous intimate contact with the surrounding particles and the cell terminals. If they become disconnected the cell capacity will decrease. Encasing the cell in a thin rigid metal case I would think would lessen the chance for the particles to become disconnected from each other. Again probably more of a problem in EV use due to mechanical vibration etc.
3. Cost: There is a large and growing market for electric vehicles and industrial uses which would use the smaller format metal cased cells. The off-grid market is probably still tiny compared to this market but can piggy back onto this market and befit it the scales of production.

The only problem I see with using smaller cells is the increased number of external interconnections. If the benefits of the smaller cells outweigh this I would think they would be the way to go.

Simon

[Living Large]

As an engineer you should know that the devil is usually in the detail. It does matter.

I can think of three reasons why smaller 20-50Ah cells in metal cases might be better than large cells in plastic cases. These reasons have been alluded to by dax who I would think knows far more than me. They are:

1. Thermal Management: Large cells, especially if they are thick and have an insulating cover will be hotter in the middle of the cell than on the edges when charging or discharging, the heat being generated by the resistive losses in the cell . It will also be harder to dissipate this heat evenly. This will mean that the middle of the cell will degrade faster than the edges. This is not so much of a problem with low charge and discharge rates, but I am sure will still be a factor.
2. Mechanical Stability: These cells are made up of vast numbers of microscopic particles each acting almost like an individual cell. For each of these particles to add to the total they must be in continuous intimate contact with the surrounding particles and the cell terminals. If they become disconnected the cell capacity will decrease. Encasing the cell in a thin rigid metal case I would think would lessen the chance for the particles to become disconnected from each other. Again probably more of a problem in EV use due to mechanical vibration etc.
3. Cost: There is a large and growing market for electric vehicles and industrial uses which would use the smaller format metal cased cells. The off-grid market is probably still tiny compared to this market but can piggy back onto this market and befit it the scales of production.

The only problem I see with using smaller cells is the increased number of interconnections. If the benefits of the smaller cells outweigh this I would think they would be the way to go.

Simon

The topic as I recall, was whether someone said one should only use large format cells, not what the relative merits are. Perhaps you were eager to open that discussion. It is useful - thank you for your thoughts.

[karrak]

Simon, I have been wanting to learn and asked questions nicely that were not answered.

Sorry, I might have missed something. Is there a question that I have not answered?

"Uh oh. Usually this indicates that the Winston was abused
...
the systems you have are just very large version of cheap cellphone chargers taken to the bigger scale."

Might I ask where you have proven that the statements above are not true?

It is not that the statements are true or not, it is the intent and context that they have been used in. Now I maybe thin skinned and there might be cultural differences between myself and the people making the comments but if these comments were aimed at me in the context that they were made in I would think they were saying that I was incompetent in the matter being discussed and that the people that were making the comments thought they were far more knowledgeable than me on this subject . If I and my company had spent more than six years researching this and successfully commercialised some products from the research, comments like those would get right up nose and I would be very tempted to write replies similar to those that were written.

Simon

[lkruper]

Sorry, I might have missed something. Is there a question that I have not answered?
Simon

They were addressed to Dak, but since you were quoting things that were said to him I assumed that the two of you were a team. I asked what was the source of the LIFEPO cells and also since a warranty of 10 years was mentioned, what the exact terms of the warranty are and the cycle life. Knowing the cost in cents per kWH per life of the battery would also be nice.

[SunEagle]

Sorry, I might have missed something. Is there a question that I have not answered?



It is not that the statements are true or not, it is the intent and context that they have been used in. Now I maybe thin skinned and there might be cultural differences between myself and the people making the comments but if these comments were aimed at me in the context that they were made in I would think they were saying that I was incompetent in the matter being discussed and that the people that were making the comments were far more knowledgeable than me on this subject . If I and my company had spent more than six years researching this and successfully commercialised some products from the research, comments like those would get right up nose and I would be very tempted to write replies similar to those that were written.

Simon

I understand your response to someone that has said something to offend you. What I am saying is that some people with knowledge on a topic may disagree with other people with similar knowledge. And you will get some people that post without any knowledge so are basically talking through their hat (not a complement).

All I ask is that while you may not like what your read or take offense from what people say it is just words, and "words and names" really don't physically hurt anyone unless they want them to.

I do appreciate the detail you provided on the "cons" of large cell LiFePO4 batteries. They makes sense and I agree that while small cell systems may have more connections that "con" may easily be outweighed by the large cell "cons".

[lkruper]

Sorry, I might have missed something. Is there a question that I have not answered?

It is not that the statements are true or not, it is the intent and context that they have been used in. Now I maybe thin skinned ...
Simon

You do appear thin skinned to me. And it is of paramount interest to ME if these statements are true or not. Lets analyze your possible responses:

1) The statements are true but you don't like the way they were presented so you use that as a pretext and won't address them.
2) The statements are false and you can prove otherwise but you won't because you don't like the way they were presented.
3) The statements are false but you cannot prove otherwise.

Which is it? This not Kindergarten.

[PNjunction]

These reasons have been alluded to by dax who I would think knows far more than me. They are:
.......[*]Thermal Management: Large cells, especially if they are thick and have an insulating cover will be hotter in the middle of the cell than on the edges when charging or discharging, the heat being generated by the resistive losses in the cell . It will also be harder to dissipate this heat evenly. This will mean that the middle of the cell will degrade faster than the edges. This is not so much of a problem with low charge and discharge rates, but I am sure will still be a factor.

Not much of a factor at our rates. Not even at 1C rates. To recap a massive discharge without heat from large prismatics at about .2C for a 400ah bank. Similar to our usage:

https://www.youtube.com/watch?v=oJ8AfJsOhsM

Things start to get warmer above 1C, which we will never go to.

[*]Mechanical Stability: These cells are made up of vast numbers of microscopic particles each acting almost like an individual cell. For each of these particles to add to the total they must be in continuous intimate contact with the surrounding particles and the cell terminals. If they become disconnected the cell capacity will decrease. Encasing the cell in a thin rigid metal case I would think would lessen the chance for the particles to become disconnected from each other. Again probably more of a problem in EV use due to mechanical vibration etc.

Makes me think of Optima or Enersys/ Hawker Cyclons One aspect of cylindrical cells for the diy'er is that now you have to build a custom cylindrical housing, rather than the prismatics which more or less stack or sit aside each other with banding and strapping for physical stability. OR, the manufacturer / distributor puts the cylindricals into a box for you. Maybe you can get the holders premade, like on the smaller scale with the Headway cells.

Again you nailed it - an EV would see the most benefit. And possibly a mobile caravan doing 4x4, stuff like that. For a stationary housebank, the prismatics are sturdy enough.

[*]Cost: There is a large and growing market for electric vehicles and industrial uses which would use the smaller format metal cased cells. The off-grid market is probably still tiny compared to this market but can piggy back onto this market and befit it the scales of production.

Just be careful about piggybacking - it can go too far, although it CAN be done. For example CALB has some higher-end cells that take incredible amounts of current, but would just represent a waste of money for us. I hope Dax's cells are reasonable, considering that we will never use the high-current capability - of which we still don't know what the specs truly are!

The only problem I see with using smaller cells is the increased number of interconnections. If the benefits of the smaller cells outweigh this I would think they would be the way to go.

That is a problem all-right but there is one more: It is easier for a failing cell to "hide" amongst the mass of others, and take down their nearest neighbors. That isn't to say that you can't have a large prismatic failure too, but when you do, you have a smoking gun to point to quickly. (um, pun not intended! )

Of course the whole mass of small cells can be connected to various wiring setups and control circuitry - from a spaghetti mess to professional. I'm sure Dax is professional about it.

I really hate to go here, but Dax has kind of forced the proposed-business issue:

Will Dax be the sole-supplier for these cells, and if so, is one comfortable with a single-vendor solution? Will he sell just the cells to interested makers, including small-fry makers, or can it only be gotten as a "system"?

So there is a big factor - if my GBS bank went down tomorrow, but since I have a lot of my own infrastructure connected to it - (ie my own LVD's, monitoring, etc), I could replace the whole lot with Winston or CALB or any other manufacturer of my choosing without a lot of infrastructure changes.

I sincerely wish him the best, but it is wise to remember that NONE OF US has demonstrated a real-world calendrical lifespan reaching the mythical 2000+ cycles (ie daily cycle, not hammering them repeatedly). Ie, nobody I know that uses LFP has ever said something like "yeah, I'm on my second bank now - my first one lasted 8 years and about 2000 cycles, so I just replaced it with the same". If a cell / bank that is sitting around between 40-80% SOC on a float-standby basis, that doesn't count for us daily-cyclers.

Thing is, instead of just talking about it, get some cells from Dax, put it together and join the fun for a small experimental bank. Or any of the prismatics. 12v even with a simple 4S setup!

I tell ya' lurkers, actually doing it physically beats the pants off talking about it.

The problem is that there will never be a one-size-fits-all solution with LFP, and thus a never ending thread.

[Bala]

Well from my point of View, Dax was jumped on by more than one person and the forum members have most likely missed out on a lot of good input due to a vocal minority who have justified their actions to make themselves feel good. It has been like a motorbike forum I know, but a sad week or two for this forum.

I live off grid, have done for over 9 years at my own house and lived in various different places with off grid solar or generators.

I dont want to buy cells and experiment, I have to many hobbies. My power supply is not a hobby, so if my next set of batteries is going to be anything other FLA I want to buy it as a drop in replacement with a warranty and a local service agent.

Dax has info that sounds promising, but raises more questions for me. I live above 25c most of the time with high humidity, bit hard to cool things down and a lot of circuit boards for balance etc will likely go mouldy and corrode, may just be to technical to be reliable.

But I hope he has it sorted and it is a viable option in the not to distant future.

I did PM him to get a name to keep an eye one for the future, if I dont get a reply no problem, I think I have found his company. But if not I am sure he will make news in the alternative energy supply circles if his plans come good.

[Willy T]

There are other Modes of Failure with LiFepo4 other that what was posted. Statements made to impune the Poster and diminish their credibility are not really anything new here.

Unreasonable numbers of cells in parallel cell lines ( search " Tasman " here ) are just as suspicious in LFP to me as in FLA, not to mention high resistance connections. A 100 amp hr prismatic 3.2v, cell / battery may already have 10-100, + / - prismatic envelope cells inside paralleled to the buss, the numbers add up fast. Anytime your having balance issues I would suspect individual cell failures.

Large format pouch / prismatic cells and thermal modeling. To focus on size of the format of the cells and the case they are inserted in may not be the only thing think about.

http://jes.ecsdl.org/content/162/1/A181.full

http://www.epectec.com/batteries/prismatic-pouch-packs.html

This looks like about a 100 amp hr, 3.2v Winston cell. How many prismatic envelope cells do you see inside this demo cell ??

ScreenHunter_910.jpg

[PNjunction]

For the Winston, basically just one. Inside is like pulling apart a very large post-it-note pad accordion style, but with a 3rd dimension-like fold in between.

But yes, you can also put together many "pouches" if you will, like a bunch of 20ah A123 prismatic cells paralleled inside a box. The A123's are a far cry from the usual "lipo" hobby crap. Many of which are just held together with a simple heatshrink when they actually need compression to keep the elements together. Aside from over or undercharge, no compression can lead to hot spots where some of the material is close together and some not. RC hobbiests with basically loose un-compressed cells discover this pretty quickly, but they didn't really pay for a decent casing.

Another failure mode that isn't commonly discussed is poor "overhang". That is the anode and cathode are not exactly equal in dimension on purpose - but if you lose compression, and then press it back together (in extreme cases), you lose your overhang, and now dendrites and other nasties can appear. That's one reason why guys who recompress an abused cell don't get the expected life back out of them. Poor manufacturers and counterfeiters may not take the time or have the precision to do this properly. The cell doesn't immediately fail, but lives long enough to make it to market and into your hands for awhile.

I dunno' - maybe if the internet had been around in our grandfather's (or great grand-dad's) day, the situation would be the same never-ending fight between conventional lead-acid and NiFe.

[Willy T]

For the Winston, basically just one. Inside is like pulling apart a very large post-it-note pad accordion style, but with a 3rd dimension-like fold in between.

So, you think there is just one with one cathode and anode connected to the clamping terminals in a Winston Prismatic Battery ?? How many foil tabs on each clamp ?? Where is the electrolyte contained in these cells ?? In FLA it's plate pairs that build capacity. I notice once you go above 400 amp hr in large format they go to 4 terminals per battery. The 1000 amp hr have 6 terminals.

ScreenHunter_952.jpg

I will saw one apart as soon as I get one to fail, but mine are functioning at the moment. As far as pouch cells go, I have never seen one over 20 amp hr capacity, not to say there are not any. The Nissan cells have 4 cells per element, they list them as a larger capacity, but it's 4, No idea how many are in a Pouch cell.

We really need a Glossary of terms, Dax say's he uses cell's of 40-50 amp capacity, when does a number of cells become a Battery ?? I call mine unit's ( 2p2s ) to keep the size and weight down to 80 lb per unit. It also cuts down on the number of paralleled batteries and makes the compression case's easier to build.

Here is a picture of part of Tasmans bank he posted. It is 12p4s ( I think ) and he reported problems with voltage consistency and balance in the cell lines. The construction does not look bad, but with that many paralleled cells your looking for a problem.

ScreenHunter_885.jpg

[lkruper]

Well from my point of View, Dax was jumped on by more than one person and the forum members have most likely missed out on a lot of good input due to a vocal minority who have justified their actions to make themselves feel good. It has been like a motorbike forum I know, but a sad week or two for this forum.

I live off grid, have done for over 9 years at my own house and lived in various different places with off grid solar or generators.

I dont want to buy cells and experiment, I have to many hobbies. My power supply is not a hobby, so if my next set of batteries is going to be anything other FLA I want to buy it as a drop in replacement with a warranty and a local service agent.

Dax has info that sounds promising, but raises more questions for me. I live above 25c most of the time with high humidity, bit hard to cool things down and a lot of circuit boards for balance etc will likely go mouldy and corrode, may just be to technical to be reliable.

But I hope he has it sorted and it is a viable option in the not to distant future.

I did PM him to get a name to keep an eye one for the future, if I dont get a reply no problem, I think I have found his company. But if not I am sure he will make news in the alternative energy supply circles if his plans come good.

I have the perfect solution for you, but I won't tell you. BTW, everybody here is wrong on the subject but I can't say why

[PNjunction]

So, you think there is just one with one cathode and anode connected to the clamping terminals in a Winston Prismatic Battery ??

No - what I mean by -one- is that they are not made of many parallel discrete-stand-alone cells. Ie, not just paralleling ten, 20ah stand-alone lipo-packaged cells together internally for a 200ah battery.

Yeah, as for Tasman's battery, that would not be my choice. But to each his own.

Back in a galaxy far away, when I first got interested in LFP, it was to prove to myself that *under our application*, one could really use the KISS method, keep cell counts down, infrastructure simple, and most importantly not have to use a spaghetti-mess of wiring or obsession about microscopic values of top-balance differences. Later I learned that doing the microscopic top-balance with dinky / unreliable bleeder boards was more or less a mind-game in our application, and merely prolongs the time one spends near full charge - where parasitic reactions over time can negate the feel-good measures of making voltmeters line up perfectly. Reasonable-balance - yes. Going overboard - no.

Heh, but we've been down that road already.

The goal was that if I couldn't KISS my LFP batteries, and had to go totally nuts with spaghetti wiring and 3rd-party control systems, then it was a no-go and would be happy to just chuck it and go back to lead-acid. Fortunately, the LFP's are still around and I'm still amazed by them using only the same sane precautions like LVD and so forth. We'll see in a few years time if I feel the same way.

In the end, whatever floats one's boat! I prefer the KISS method since it gives me a whole lotta' latitude, but that may not suit others.

BTW, that first pic shows what appears to have been an early model Hi-Power cell with the dissimilar metal problem internally. By now, most manufacturers of high quality try not to repeat that mistake.

[Willy T]

No - what I mean by -one- is that they are not made of many parallel discrete-stand-alone cells. Ie, not just paralleling ten, 20ah stand-alone lipo-packaged cells together internally for a 200ah battery.

Maybe were just talking about the semantics of manufacturing. What do you see in these pictures of this GBS battery ?? Do you not see many paralleled cells with separate cathodes and anodes for each cell ?? I guess I don't understand what your visualizing as stand alone and expressing. Of course there is no free electrolyte as each cell is wetted in individually. " Stand alone " ?? If separated you'd certainly have Individual cells. The Power point drawings you'v seen make you think they are all joined.

There 80 cells in this battery, two sections of 40. I don't know the amp hr capacity of the total.

ScreenHunter_138.jpg


ScreenHunter_139.jpg


The point was / is that individual cells age and fail differently and the over all mode of failure is not always operator error. As a cell deteriorates it effects the capacity of the battery.

[PNjunction]

What I mean is that they are not made of many of these types individually totally wrapped:

http://www.a123systems.com/prismatic-cell-amp20.htm

Although yes, you *could* do that, although some E-bikers / bench hackers did not get them from authorized dealers, and paid the price shortly afterwards.