LiFePO4 for House bank final designs

[Maine Sail]

Originally Posted by alctel

It was, yeah. He said Sinopoly had discontinued larger than 200AH - this was a recent thing, a few months ago.

I think after 3 years you are probably fine!

CALB has done similar because the demand for 180's and smaller is eating up production. They can technically still build 400Ah cells but have not for a while.

[toddedger]

Mainsail
"When you use smaller cells you have no choice but to put LFP cells in parallel and this could present a <i>potential</i> safety issue, if one cell were to internally short or fail. "

I still don't understand this statement. Why would an internal short of a 100 ah cell in parallel with three other 100 ah cells be any more of a safety issue than an internal short of a 400 ah cell?

[Maine Sail]

Originally Posted by toddedger

Mainsail
"When you use smaller cells you have no choice but to put LFP cells in parallel and this could present a <i>potential</i> safety issue, if one cell were to internally short or fail. "

I still don't understand this statement. Why would an internal short of a 100 ah cell in parallel with three other 100 ah cells be any more of a safety issue than an internal short of a 400 ah cell?

It is the difference between a series wired bank and parallel/series bank.

A 400Ah 4S pack made from 400Ah cells has no cells in parallel. A short or failure in one cell causes that cell to self discharge to a lower voltage maybe even 0V over time. It may get warm when this occurs on its own, stand alone, but if you kept feeding it current, from paralleled cells, you run the potential for a more drastic heating event and possibly even thermal run away.

A 400Ah pack made of 100Ah cells has 4 sets of 4 cells in parallel. If any one of the paralleled cells should fail internally we now have 300Ah of good cells feeding into the failed cell.

Again this is rare but it could happen when cells are paralleled..

[OceanSeaSpray]

Let's assume that a small cell in a 4x100Ah parallel block fails by shorting internally: not only it will eventually discharge its own stored energy into the fault, but the other three cells will as well.

Now, the point to remember is that problems only become accidents with LFP if a hot spot within a cell manages to reach about 200degC. At that point, the oxygen unbinds from the FePO4 cathode material and starts a fire with the carbon and the electrolyte in the cell.

A small cell in a 4P block can potentially receive a lot more discharge energy for its mass than a larger cell just shorting out its own capacity, so you could say that you are more likely to reach that runaway temperature threshold with cells paralleled in blocks. A single cell only has its own stored energy to deal with and proportionally more mass to heat. When you see them venting etc and never catch fire, it is because they run out of charge before having become hot enough.

Now, I am not aware of a prismatic cell ever shorting suddenly and heavily without a good external reason, but it "could" happen, which is also what Sinopoly told me when I asked them. Cells that failed in service for "no reason" have done so by gradually self-discharging more and more. First they create pack balance problems that can't be fixed and it ends with the whole parallel block destroyed through over-discharge if nothing is being done about it.

So the main commercials only sell 4S and 8S packs because they don't want to be held liable if it ever went wrong and, if you want more capacity, you can parallel these individually-protected packs. Meanwhile we quite often build parallel-then-series packs because it is easy, simple and lower cost and the risk seems more theoretical than anything.

Now if I have to choose between 4S using large cells or nP4S using small cells, I will do the latter every single time, because the small cells have a much higher structural strength-to-weight ratio (Sinopoly application engineer here again). If the internals of the cells are moving when the boat moves (and this has nothing to do with "vibration") sooner or later the cells will fail internally due to chafe and mechanical damage.

The big cells that failed completely did so on boats that had completed ocean passages, not on boats spending their time in marinas or rarely going out and when the sea is flat. Remember that not only Rolf's cells failed, but also another set on another multi with the same setup. They suddenly started self-discharging and the banks became completely unmanageable.

Now, what is "too big"? Sinopoly say >200Ah. The commercials build their packs with cells <=200Ah as well, whether they are Sinopoly, CALB or else. So I will stick with 200Ah max. There is zero gain or benefit to be found in trying to find and tease the limit. None.

The best way to cause a prismatic cell to short out heavily and potentially catch fire is whacking it around its short sides. Forget about driving nails into them etc. Hit the short sides really hard and you can cause the plate edges to fold onto each other inside and really short it out. So go out there and fall off a 4-5 metre wave and see what happens to that 4S 400/700/1000Ah bank. It could be really entertaining.

[toddedger]

Thanks to both mainesail and oceanseaspray for your answers. You both make very valid points, and I really appreciate you guys taking the time to explain your thoughts on the subject.[emoji3]

In my mind the 400 Ah cell has just as much energy to discharge in a short as the parallel bundle. Yes I agree there is more mass in the the larger cell, but also remember that the parallel bundle is tight together forming additional mass to help dissipate heat. I guess it comes down to personal preferences on the trade off over the risk of more heat in a short versus greater chance of having a short in the first place.

[OceanSeaSpray]

Originally Posted by toddedger

In my mind the 400 Ah cell has just as much energy to discharge in a short as the parallel bundle. Yes I agree there is more mass in the the larger cell, but also remember that the parallel bundle is tight together forming additional mass to help dissipate heat. I guess it comes down to personal preferences on the trade off over the risk of more heat in a short versus greater chance of having a short in the first place.

Well, it is very much a matter of personal preference indeed as long as you are dealing with your own risk, which is what makes all the difference...
If you use this reasoning to push the cell size up, then it doesn't hold any more, because on one side you have a risk and on the other a certainty awaiting the right time or circumstances to materialise.

Also, I wanted to say that if you are dealing with a 10P4S system, you should easily be able to calculate cell fuses and mitigate the matter of a cell shorting out; in a 2P4S system, it is usually a lot more problematic.

The energy is the same as you say quite rightly, but when it comes to the greater mass, not any more when it is spread over several cells. The casings act as insulators, they often have grooves and the heat is just not going to flow fast enough. Technically, you just need one spot getting hot enough to start the combustion process. The smaller the cell and the more energy available... the quicker you can get there.

Parallel blocks are a long way down my list of concerns I must say. Excessive cell weight/size is near the top.

[PacificGreen]

When we look at the Volvo 70 racer Team Vestas Wind and the report released thereafter in relation to the lithium batteries accompanied by photographs of the engine compartment some conclusions can be reached:

1) The batteries didn't appear to be secured well at all. Only secured by some type of I-rail system 1/3 the way up and it doesn't appear to be secured from traveling north or south longitudinally either. If this was the actual state at the time of impact is unknown.

Source: http://www.panbo.com/assets_c/2015/0...auto-11392.jpg

2) This boat was put to sea in a hurry.
3) The boat did not stop completely at impact:
sailing at about 16 knots at the time of impact. The boat did not stop dead as if it had crashed into a brick wall but did pull up very quickly, reducing speed to less than 3 knots within 10 seconds and stopped within the next 10 seconds. This slight cushioning effect of the breaking daggerboard and the multiple impacts on the reef probably prevented serious injuries. Source: http://www.panbo.com/assets_c/2015/0...auto-11392.jpg
4) In point 82 they say the engine was started but ineffective.
5) In point 83 the jolting is described as extreme. See point 1 above then read point 83 again.
6) From 7:30 to 9:15 the batteries were still providing power and up to 40 minutes after that.
7) Then come points 247, 248 and 249 that describe the immersion of the batteries in saltwater and smoking of batteries, the subsequent decision to abandon based on that as one factor and the ultimate demise of the battery on the beach after having suffered what must have been a thermal meltdown. Fairly hot potato to be carrying to the beach.

Drawing conclusions for battery sizes based on mass of batteries and using this grounding as an example is debatable. Here this conclusion draws some rather unfounded examples as well:

Lithium batteries fundamentals | Nordkyn Design

The document blames the failure on immersion in seawater, but a simple calculation based on the conductivity of sea water shows that this would only result in discharge currents of a few amps. Water ingress within the cells is also unlikely due to their sealed nature, the lack of water pressure and the fact that the relief valve is designed to open on internal over-pressure.

Water ingress into lithium batteries may create a meltdown that can result in a fire and explosion. He goes on to say:

A tentative explanation is that the shock from the sudden impact at high speed caused the elements within the cell casings to shift, bruising the edges of the plates and creating a short-circuit. The cells themselves were of standard 180Ah/3.2V LiFePO4 prismatic construction.
If the violent impact indeed caused them to short-circuit internally, then it illustrates the foolishness of using large format LFP cells for building marine house banks as some have already done, sometimes resorting to 400Ah or even 700Ah individual units. It would also greatly strengthen the case for mechanically clamping the cells together.

Which then gets repeated here more or less. What actually occurred is the entire force of the boat moving longitudinally and launching the batteries in the 8" of space that is present to the top and bottom of the batteries if you magnify the picture and look.

That force was extreme longitudinally and damaged a few terminal bolts and probably cracked the area around the studs. They continued to produce energy until as the facts state they were immersed in sea water and the reaction accelerated exponentially thereafter.

Seawater exposed to non discharged batteries causes smoke and lots of it, especially if there was a route for it to penetrate and after the beating this bank took there likely was damage to the cells.

If there is no way for the water to enter then there can only be electrolysis.

Water had ample time to find its way into any number of the not completely discharged cells. So far as I am aware none of our batteries have IP68 rating but they do have UN38.3 Ratings:

lithium & solar power LiFePO4
http://www.faktor.de/out/media/WB-LY...UN38.3-Eng.pdf
http://www.faktor.de/out/media/WB-LY...UN38.3-Eng.pdf
http://www.faktor.de/out/media/WB-LY...UN38.3-Eng.pdf

Different tests that all manufactures must pass are interesting and they all follow the same format to pass the UN38.3 test for the most part.

Suffice to say most lithium batteries no matter the size will remain intact on a boat provided you don't allow it to slam around with more force than is in the test - be that 8G of vibration or repeated full force weight drops of more than 20 lbs at 2 feet on any side of the battery.

When you examine the composition of the internal layout of the prismatic cells we are all using they are fundamentally the same in their composition with each having their own terminals bolted to copper and aluminum electrodes surrounded by the cathode, separator and anode ribbon.

The mass remains for the most part the same in terms of energy storage if you go series or series-parallel your cells. What doesn't remain the same are the odds of having an internal short due to more connections and exponentially so regarding serial and parallel connections.

The very nature of bus bar connections in and of itself will lead to, on a forceful impact of unsecured batteries, a crack likely occurring at a terminal bolt. The meltdown from there into paralleled-series cells is catastrophic and the reaction will have to continue.

The following picture can be used to illustrate. While not entirely related to bus bar damage it very well could have been:
Source: http://liionbms.com/images/prismatic...ction_side.jpg


Whereas the same thing happening even with series aligned cells results in a loss of only that particular cell or cells and reduced voltage from your string. Now this is detrimental in 4S strings only for the most part because if you loose 1 cell your at 9V but from a 48v pack you still can run everything at a reasonable but reduced voltage even if you have to remove a cell and that is a factor of redundancy. The other factor of redundancy are having larger terminal bolts to begin with.

Now we can speak in terms of mass as it relates to vigorous movement and here is a good example:

lithium & solar power LiFePO4

While obviously not a boat 160 100ah cells has a specific weight that was carefully contained and not allowed to move. The result would not have been any different if they had used 1000ah cells to make the same amount of energy storage. Succinctly put if you were to jump it off a 5 meter sand dune you better brace for impact and stop to immediately check every cell in your pack and make repairs or initiate safety protocols regardless of cell size or configuration.

The same amount of energy storage potential is available in larger cells and smaller cells. They are all packed the same. Thus any movement of smaller cells with the same energy potential as larger cells results in the same chance of the rare internal short except that with larger cells there may be more robust bolting on the interior of the cells simply due to the size difference. A picture of one would be worth a thousand words.

We can further extrapolate that any salesman using such obvious pressure sales tactics to elicit a sale does so because bigger cells are perhaps not in stock or other reasons. In the end though we have all bought lithium batteries of one type or another and it is threads like this that bring about their strengths and weaknesses as they relate to our everyday use and brings about changes hopefully for the better of all. How secure are your batteries?

[exMaggieDrum]

Originally Posted by ColdEh Marine

Was that Randy at CanEv ?

I got 8x 300 amp hour sinopoly's from him and he knew they were going into my boat.

Quick edit , to add my cells have been fine and running for almost three years steady.

Regards John.

I bought my Sinopolys from Randy. He was great to work with but with a long lead time and full payment in advance. The CanEv business is only for electric vehicles and not any marine or heavy shock use. I don't think it would be something he would even think about ,or if he had, would leave it to the customer to make their own decisions. Mine were only 100Ah cells so perhaps he didn't think it important to bring up even if he did think about it but I bet not. He really didn't want to spend any more time with me than necessary to get me my cells as that would take away from his far larger main business.

[Typhoon]

Originally Posted by exMaggieDrum

I bought my Sinopolys from Randy. He was great to work with but with a long lead time and full payment in advance. The CanEv business is only for electric vehicles and not any marine or heavy shock use. I don't think it would be something he would even think about ,or if he had, would leave it to the customer to make their own decisions. Mine were only 100Ah cells so perhaps he didn't think it important to bring up even if he did think about it but I bet not. He really didn't want to spend any more time with me than necessary to get me my cells as that would take away from his far larger main business.

I will deal with Randy again when I build my back up LifePo4 bank. Yes you have to pay up front , just like everything else you buy from the Internet. Nobody wants to order and be responsible for your item before getting paid . I agree lead times are long, but he has to piggy back our boat orders with his regular shipment from China . At least he picks up his phone and answers emails , and the batteries come. I am very pleased.

Thumbs up to Canadian Electric Vehicles Ltd.

Regards John.

[exMaggieDrum]

Originally Posted by ColdEh Marine

I will deal with Randy again when I build my back up LifePo4 bank. Yes you have to pay up front , just like everything else you buy from the Internet. Nobody wants to order and be responsible for your item before getting paid . I agree lead times are long, but he has to piggy back our boat orders with his regular shipment from China . At least he picks up his phone and answers emails , and the batteries come. I am very pleased.

Thumbs up to Canadian Electric Vehicles Ltd.

Regards John.

I agree John. I was happy working with Randy. He came through for me. He was a little backed up on email a bit but always got back to me. But it is not everyday that I pay $2000+ direct to a company I have never dealt with before, in a foreign country, and had to wait for 3 months after prepayment, and he told me that the shipment might take an indefinite time longer. I was a bit nervous. But it all worked out and I would work with Randy again if needed.
Joe

[Typhoon]

Yes . When I read about the trouble people were having trying to get cells , I almost gave up on the whole thing . Finding Randy was a stroke of luck . My cells cost me 3800$ Canadian and of course all up front as well , it was a little nerve racking for sure .

Regards John

[andreas.mehlin]

Where In Mexico or Panama can I buy LiFePO4 batteries? 3.2 400Ah.
EV-Power.eu only shipping the batteries within Europe due ADR. Or do you know any shipper (sea?) who is ok with bigger LifePO4??

[pacific_voyager]

Note: Some Programming instructions from Balmar for using MC-614 or MC-612DUAL voltage regulators with Lithium Iron banks are available here. I can't vouch for the settings (they may be a bit high) but this is what they gave me. It still does not shut off when done, like it should. That needs to be handled externally by disconnecting the power or switch wire.

[roostermt]

Hi guys,

Putting my setup together. Having a hard time finding a BMS that works for the boat. I'm putting together 540 AH 12 cells.

Any thoughts on a BMS that is currently Available.

Rooster