LiFePO4 - The future for off-grid battery banks?

[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?
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.

[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

[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]

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

[PNjunction]

Time for an apology and a clean slate!

Maybe I should have made myself clearer. I and Dax are not talking about small 18650 cylindrical style batteries and certainly not taking about anything else but LiFePO4 based cells. As Dax has said the cells they are using are 40/50Ah LiFePO4 cells.

Somehow I missed that, so I'll kick the whole thing off with a clean slate as it is getting out of control even for us with thicker-skin.

Dax - I apologize. This whole thing has obviously created some gray hairs, and nobody needs that. I owe you a cold Toohey's or whatever is your beverage of choice.

While cells this size would not be MY preference for a large diy bank, it is do-able.

[Living Large]

If I read it correctly, PNJunction has stated that "we" should only use Large format Prismatics for off-grid system. I want to know on what basis he gives this advice.

Simon

Considering PN answered your question an hour before you posted this, there is no need to reply. 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.

[Willy T]

There are so many different, Manufacturers, Types of cells, Chemistries, Charge / Discharge schemes, Voltages, SOC's, DOD's and Temperature variations to ever come to any conclusion on what lifespan outcome anyone could expect from a given LiFepo4 cell / battery. All these opinions are dizzying to read. Some have them, some don't and some never will and it's all speculation based on nothing or backed up with worthless data based on nothing but a assumption. The difference between individual cells ( cylindrical or flat pouch ) and prismatic batteries where you can have it stuffed with 100's envelope cells is as different as Mars and Earth, trying to extrapolate between the two is useless.

If someones battery last's a month and someones last's 10 years it really proves nothing, except the average is 5 years. Simon has posted the cumulative I/O data of his system. While it seems simplistic, it cuts to the chase, if you want to know more, ask him.

Below is about what you can expect from all the variables of managing LFP batteries ( and not using the correct charging voltages & temperatures as DAX, PNJ and others have posted ), really not all that much different from FLA at 3 time's the cost. If you can live at less than your design capacity, then they may work for you for some time. Everybody thinks they can do a better job with their batteries than the other guy, including me at times.

( From the Bus Guy at technomadia )

So how well have our batteries aged?

When our 500AH batteries were a year old (August 2012), I was able to drain 442Ah from them before having the EMS trigger a low-battery alarm cutoff.

When they were nearing 2.5 years old (November 2013) I was able to drain 409Ah before the system shut down.

Last month (December 2014), during my most recent drain test, I was only able to drain 378Ah before cutting out.

In other words – our batteries seem to be aging way faster than they should – now giving us just 75% of their original rated capacity.

Why? What could be going wrong?

[lkruper]

I don't see much evidence of some people trying to understand anything.

Maybe it is hard to remain civil after these sort of comments.

"You still have a problem and did not learn what the mistake was. You over discharged your battery, or you over charged them take your pick. The problem surfaced because you did not monitor the batteries an dvoltages. Cell size and format does not matter. Size only matters if you are a ....... "

and

"Uh oh. Usually this indicates that the Winston was abused, or the infrastucture (high-resistance connections) and so forth, or an initial "sanity check" was never done on the factory balance. Failed "bleeder boards", new-old-stock, shipping damage can be an issue, and the biggest one is this:
...
This is the tactic used by el cheapo battery manufacturers that stuff their cases with whoever is the lowest bidder, and the consumer has no idea what the quality of the cells are inside.

Don't take this personally - seeing that, I would never be interested in your systems and run away as fast as I could. As it stands now, the systems you have are just very large version of cheap cellphone chargers taken to the bigger scale."

Simon

Simon, I have been wanting to learn and asked questions nicely that were not answered. Might I ask where you have proven that the statements above are not true?

Tis not, Taint So! doesn't really prove anything.

[SunEagle]

I don't see much evidence of some people trying to understand anything.

Maybe it is hard to remain civil after these sort of comments.

"You still have a problem and did not learn what the mistake was. You over discharged your battery, or you over charged them take your pick. The problem surfaced because you did not monitor the batteries an dvoltages. Cell size and format does not matter. Size only matters if you are a ....... "

and

"Uh oh. Usually this indicates that the Winston was abused, or the infrastucture (high-resistance connections) and so forth, or an initial "sanity check" was never done on the factory balance. Failed "bleeder boards", new-old-stock, shipping damage can be an issue, and the biggest one is this:
...
This is the tactic used by el cheapo battery manufacturers that stuff their cases with whoever is the lowest bidder, and the consumer has no idea what the quality of the cells are inside.

Don't take this personally - seeing that, I would never be interested in your systems and run away as fast as I could. As it stands now, the systems you have are just very large version of cheap cellphone chargers taken to the bigger scale."

Simon

Well part of learning to live and post on an open forum like this (and others) is to grow a thick skin and not let what some people say bother you.

So while you may have been offended by those responses they do not reflect everyone's feelings.

I am looking forward to understanding how the LiFePO4 technology has evolved and I feel you and Dax have something to contribute to this forum. I do not want either of you to provide anything that can hurt your business but as an engineer I like to understand what is being said so I yearn for details.

What you want to share is up to you. Just know that while some of us may disagree on what the top battery chemistry is that doesn't mean all of us don't want to understand LiFePO4 technology.

[karrak]

My recollection is that dax had advised to avoid large format cells. So the issue is not that using large format is better, but that it was cautioned against.

Advantages and disadvantages, assuming both can reliably perform the task, is a totally different topic. Unless you consider can't reliably perform the task a disadvantage, that is.

If I read it correctly, PNJunction has stated that "we" should only use Large format Prismatics for off-grid system. I want to know on what basis he gives this advice.

Simon

[karrak]

Talking down to someone that is trying to understand what you are doing does not help them understand or win you support. What you are doing is the same as those that you are complaining about that have belittled LiFe batteries. Neither form of communication is professional or acceptable.

I don't see much evidence of some people trying to understand anything.

Maybe it is hard to remain civil after these sort of comments.

"You still have a problem and did not learn what the mistake was. You over discharged your battery, or you over charged them take your pick. The problem surfaced because you did not monitor the batteries an dvoltages. Cell size and format does not matter. Size only matters if you are a ....... "

and

"Uh oh. Usually this indicates that the Winston was abused, or the infrastucture (high-resistance connections) and so forth, or an initial "sanity check" was never done on the factory balance. Failed "bleeder boards", new-old-stock, shipping damage can be an issue, and the biggest one is this:
...
This is the tactic used by el cheapo battery manufacturers that stuff their cases with whoever is the lowest bidder, and the consumer has no idea what the quality of the cells are inside.

Don't take this personally - seeing that, I would never be interested in your systems and run away as fast as I could. As it stands now, the systems you have are just very large version of cheap cellphone chargers taken to the bigger scale."

Simon

[karrak]

The number 1 reason is that small-format cylindrical cells have far more performance than we need in our relatively low-current application. That is, why pay for cells with a capability of 10C charge / discharge when you won't actually do that with a properly sized bank for capacity and autonomy? EV's certainly. Us, no.

Maybe I should have made myself clearer. I and Dax are not talking about small 18650 cylindrical style batteries and certainly not taking about anything else but LiFePO4 based cells. As Dax has said the cells they are using are 40/50Ah LiFePO4 cells.

Simon

[PNjunction]

Can you please explain the technical reasons why large-format cells prismatic cells in plastic cases (i.e. Winston, CALB etc) should be better that smaller format cells in metal cases?

Happy to!

The number 1 reason is that small-format cylindrical cells have far more performance than we need in our relatively low-current application. That is, why pay for cells with a capability of 10C charge / discharge when you won't actually do that with a properly sized bank for capacity and autonomy? EV's certainly. Us, no.

Overall complexity - so far I have only been discussing the DIY aspect, and not commercial usage. Never planned to, but we always seem to go beyond the readers of this thread and concern ourselves with the guy next door - who isn't a participant! Large format prismatics cut down the complexity of your wiring infrastructure.

Using large format prismatics are also not behind a walled-garden inside a box you can't see like with small cylindricals. Thus you can't verify the quality of the wiring, nor does it make it easy to spot a cell which may have a problem, but is easily electrically hidden amongst the mass of others.

Small cylindricals make prime targets for grey-market, counterfeit, factory rejects, laptop-pulls, new old stock, constantly changing lowest-bidders and the like. Remember the recent Nissan-Leaf crash cell drama? Yes, stuff works, but some like to just overcomplicate the whole thing. At some point, over-complication becomes a performance and safety issue unless you are a certified commercial manufacturer with the warrantee and resources to back it all up.

Take a look at a MasterVolt LFP, and you'll see - and you'll pay too.

It kind of comes full circle to my mantra : since we aren't in an EV like application, why use EV-like cells with all what entails above just an added worry.

Let's put it this way with something closer to home for many:

I consider Enersys (Odyssey for consumers) some of the best performing pure-lead agm's on the planet. Note that I didn't say longest lasting. If I wanted to build a 500ah bank, would I do so with a massive array of 5ah Enersys / Cyclon small cylindricals, even if they are the best small lead-acid small cylindricals on the planet too? No way, and I even KNOW what I'm buying!

[solar pete]

Dax

I appreciate you sharing some of your knowledge and data concerning your battery. I am happy your business is taking off and it sounds like the LiFePo4 technology is finally maturing into a worth while energy storage system.

What I do not appreciate is your demeaning manor. Talking down to someone that is trying to understand what you are doing does not help them understand or win you support. What you are doing is the same as those that you are complaining about that have belittled LiFe batteries. Neither form of communication is professional or acceptable.

So I ask that you please continue to access this Forum and provide any help that you can on this technology without revealing any business secrets. Thank you.

Well said SunEagle, Dax you sound like some spoiled brat to me, if you dont like this place leave no one will miss you.