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Old 24-01-2020, 10:20   #16
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Re: Casing for Aluminum Cells

The Fortune Aluminum case cells shown in the video would seem to be easy to connect in a modest size bank where all of the cells are arranged in a row as shown. In a large install, of say 1000AH/12V and 10P4S, the way the bus bars are recessed would limit your ability to run them any other way other than at right angles to the cell. That might be a deal breaker depending on how you need to arrange the cells, without excessive cabling.

As far as the conductivity of the cases and the impact of seawater, all things considered I would want the cells AND all of the associated hardware (BMS, Relays and Disconnects, Fuses, etc..) to be in an area that is VERY well protected from water anyway. If that area gets submerged I have a REALLY MAJOR problem no matter what kind of cells I am using.

It would seem that the real question that we don't have a clear answer on yet is if compression is necessary on all aluminum case cells. It certainly appears that it is NOT on some brands. I would think that a clear understanding of that along with the cooling and airflow requirements are the most important.

I think I am still leaning towards the encased cells (Winston probably).
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Old 24-01-2020, 10:21   #17
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Re: Casing for Aluminum Cells

Not refurbished, 3 brand new Narada 48v batteries used in telecoms systems throughout the world.

2x 48v 50ah batteries stripped to build 12v 400Ah bank, 1x 48v 100Ah stripped down to fit but remains 48v 100Ah.
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Old 24-01-2020, 10:40   #18
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Re: Casing for Aluminum Cells

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Originally Posted by mikedefieslife View Post
I don't think we have to worry. markcouz seems to keep reiterating it but has not shown any manufacturer data, or any evidence. No-one else ever seems to have heard of such an issue either. Perhaps he's had a bad experience with a specific brand of cells in the past.

I'm more than happy to be shown to be wrong, but I do have to be shown.
has a lot to do with how the poles are insulated from the case . Mine ( blue ones ) are insulated by a big plastic grommet.
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Old 24-01-2020, 10:45   #19
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Re: Casing for Aluminum Cells

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Originally Posted by markcouz View Post
Not refurbished, 3 brand new Narada 48v batteries used in telecoms systems throughout the world.

2x 48v 50ah batteries stripped to build 12v 400Ah bank, 1x 48v 100Ah stripped down to fit but remains 48v 100Ah.
would really be curious to see the tops of the individual cells . To see just how they are built .
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Old 24-01-2020, 10:48   #20
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Re: Casing for Aluminum Cells

Apparently this was a decent thread to start, as it seems to be split between. I have put in an order request for the Fortune cells - Thanks for posting that! Thats exactly what I wanted to achieve.
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Old 24-01-2020, 11:37   #21
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Re: Casing for Aluminum Cells

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would really be curious to see the tops of the individual cells . To see just how they are built .

Hope the pic is viewable, 1st attempt.
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Old 24-01-2020, 12:32   #22
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Re: Casing for Aluminum Cells

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The Fortune Aluminum case cells shown in the video would seem to be easy to connect in a modest size bank where all of the cells are arranged in a row as shown. In a large install, of say 1000AH/12V and 10P4S, the way the bus bars are recessed would limit your ability to run them any other way other than at right angles to the cell. That might be a deal breaker depending on how you need to arrange the cells, without excessive cabling.
You can run bus bars in both cardinal directions. You use longer ones to make the "sideways" connections.
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Old 24-01-2020, 12:36   #23
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Re: Casing for Aluminum Cells

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I don't think we have to worry. markcouz seems to keep reiterating it but has not shown any manufacturer data, or any evidence. No-one else ever seems to have heard of such an issue either. Perhaps he's had a bad experience with a specific brand of cells in the past.
I just wrote above that my manufacturer said to separate the cells to prevent leakage.

When I look at pictures of their huge bank builds, they use spacers.

Can you not do it and get away with it? Probably.

Are there other aluminum-case cells that are well-enough-insulated that it's not necessary? Probably.

But aside from electrical considerations, what I can tell you from direct observation with my thermal camera is that these cells do heat in their centers, and concentrating that heat in the middle of a long row is going to change the behavior (Ri, performance, capacity) of the innermost cells before the outer ones. Adding the air gap allows a bank of cells to shed heat more evenly.

So I think it is a reasonable precaution to design a large pack this way, regardless of whether you can get hard data on what "must" be done.
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Old 24-01-2020, 12:40   #24
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Re: Casing for Aluminum Cells

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You should check out this guy's youtube channel (no affiliation).
These look like the cells I use.

Except, my spacers have holes in the short sides, to allow the bus bars to extend in either direction.

At the time, these were the most attractive (density, geometry) cells available on the market. There are some new cells now that pencil out even denser on paper, but I think I would want to have a few of them in my hands before committing to building a large pack out of them.
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Old 24-01-2020, 13:55   #25
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Re: Casing for Aluminum Cells

Yeah, you can see in the shot above how the plastic spacer would prevent (or at least make much more difficult) a connection from the short side.

The fact that you are seeing heat in the middle of the case on the aluminum cells makes me think that the plastic covered cells would do the same, but not be able to shed the heat as easily. For the c-rate that most of these are discharged its probably not of any significance. However it does seem like the aluminum cells with proper spacing would be a better situation. I am probably overthinking this, but its a REALLY big investment when your talking about 1000 AH or bigger. I also have a few months before I will even have a boat to put them in, much less be able to make a final design choice and start buying them. I might as well learn all I can now.

Prior to this morning I didn't even realize that the aluminum didn't require compression like the others. I wish I new more about the actual internal design differences.

Nebster, what brand of cells are yours?

Thanks Qismat for starting this thread!
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Old 24-01-2020, 14:16   #26
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Re: Casing for Aluminum Cells

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The cells that I used where stripped from new Narada 48v battery, I can't show you evidence because I live 1500km from the boat.

I have no reason to make this up, but I have been an electrician for 30 years so please be assured that I am comfortable with the function of a voltmeter.

I have no experience of other aluminium cased cells, only my own. I assumed that what I found would apply in general- glad to hear that is not the case.

However I do think that others should be aware of this possibility and take precautions if necessary.
I wasn't necessarily accusing you of making it up, more I wanted to see something written somewhere by a manufacturer of the type of aluminium cells most boaters with DIY packs would be using.

The ones you were using are different to the ones supplied by RJ Energy and other blue aluminium cells. The fact that you've stripped them from a commercial battery which they were probably designed for, likely has something to do with it.

I'll ask my manufacturer, though I imagine anything other than a paper think spacer would mean that the bar connecters no longer fit.
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Old 24-01-2020, 14:33   #27
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Re: Casing for Aluminum Cells

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Originally Posted by mikedefieslife View Post
I don't think we have to worry. markcouz seems to keep reiterating it but has not shown any manufacturer data, or any evidence. No-one else ever seems to have heard of such an issue either. Perhaps he's had a bad experience with a specific brand of cells in the past.

I'm more than happy to be shown to be wrong, but I do have to be shown.
It's a mode of failure seen enough that I have a training slide. The two photos and CT image are from the first of the Boeing 787 battery failures and are typical. The lower left photo shows a hole molten through a layer of aluminum and one of stainless, so there was some serious power in the short circuit. I can't tell you how much power we calculated but one of the Teslas I investigated had a several inch diameter hole blown though layers of steel, external insulation, and the aluminum car body. Cell to cell case shorts or shorts to a metal housing have happened in devices crushed in airline seat recliners, toys, and EV crash damage which impinges through the aluminum case into the cells.

The illustration in the upper right contains 4 cells in a metal housing. The cell on the right shows how discharge energy works its' way from the thin anode/cathode foils to the thicker current collectors, then those are collected at the header for connection to the cell terminals. Like a tree trunk to branches to leaves, each layer is strong enough for its' own intended function. The cell on the left is similar to where the molten point occurred in the 787 case. Rather than energy going up, the short focuses energy at the failure, initially from just that one cell (the yellow box) which almost instantaneously puts additional energy into the foils and electrolyte as heat.

LiFePo4 and some of the other cell chemistries generally have what we call soft failures, in that an internal short creates heat, but it and possibly a venting are not near instantaneous so we consider LiFePo4 "safe." But there have been fires in packs of LiFePo4 metal cells.

What makes metal to metal case shorts a real problem is that the energy from a series of upstream cells gets added into the foils and rapidly melting separator as resistive heat. The energy going into the short is not just of the one cell, rather the energy is multiplied by the number of upstream cells plus the shorted one. Since this energy is added to electrolyte also going out the hole, the failure has fuel, oxygen, and kilowatts turning into heat.

One thing the illustration does not show is that the outer box will usually be found to have a grounding path through its' mount. Initially one would think that the problem could be mediated by making absolutely sure there is no path from the outer case (or aluminum compression plates) into the vehicle ground. That creates an electrical problem in that the housing may be a different potential, which is bad especially in airplanes and cars which can develop significant static charges. Isolation is sometimes done as good design practice by severing the ground path in the event of overload, but the reality is that by that point the energy dumped into the short has already been enough to melt the case and start a cascade. Plus, once the (semi) conductive electrolyte is released everything will be contaminated by it. Obviously, having water between the cells would be a conductive path to avoid in a good design.

Hope this helps.
Bob

btw - This is entirely about potential grounding failures and is NOT about whether or not to restrain cells. As I've said before you need to follow manufacturer guidance about that. If the cells are restrained in a way which can develop compression, I've ONLY seen it so the restraint is against the full face of the cells. Having just a bar or narrow plate going across would not be a good practice.

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Old 24-01-2020, 16:38   #28
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Re: Casing for Aluminum Cells

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Yeah, you can see in the shot above how the plastic spacer would prevent (or at least make much more difficult) a connection from the short side.
Yeah. Hunt around online for the batteries, and you'll see good photos of the alternate spacers that permit more wiring arrangements.

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The fact that you are seeing heat in the middle of the case on the aluminum cells makes me think that the plastic covered cells would do the same, but not be able to shed the heat as easily. For the c-rate that most of these are discharged its probably not of any significance.
I mean, the amount I can see is a gradient of just over 1degF in cool, open air at 0.25C. But that heating could easily accumulate in a tightly-packed battery. It wouldn't surprise me to learn that the middle of a dense pack under load could reach 10F warmer than the edges even at fairly low rates.

I suspect this concentrated heating could be part of why so many people observe performance imbalance on the interior cells of their packs. The warmer parts of the cells are changing faster.

For those of us who want to avoid a balancing BMS situation, keeping all of the cells at the same temperature seems like a prudent goal.

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However it does seem like the aluminum cells with proper spacing would be a better situation. I am probably overthinking this, but its a REALLY big investment when your talking about 1000 AH or bigger. I also have a few months before I will even have a boat to put them in, much less be able to make a final design choice and start buying them. I might as well learn all I can now.
The density advantages of the metal-shell batteries were the real driver for me.

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Prior to this morning I didn't even realize that the aluminum didn't require compression like the others. I wish I new more about the actual internal design differences.
My theory -- and it's only my own -- is that the manufacturers don't really know, so they guess. Long ago, they had lots of issues mismanaging the chemistry (in plastic shells). One result of that was expansion, and one partial mitigation for that expansion was to prevent it with compression.

15 years later, everyone understands a lot more about the performance envelope for this chemistry. Designing the enclosure with enough space for the (very nominal) slight expansion at rate may be a change that has been made. But, more importantly, we storage system users can just design our circuit to eliminate any chance of swelling in the first place. That's, surely, strictly better for the lifespan of all of these batteries, compressed or not.

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Nebster, what brand of cells are yours?
That brand "Fortune" that you see I believe is just a name some USA importer made up to obfuscate their source. They are actually made by Jiangsu Frey. I bought my cells directly from a rep in Shenzhen who sells cells from various factories. If your quantity will be >50, let me know and I can put you in touch with her.
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Old 24-01-2020, 21:55   #29
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Re: Casing for Aluminum Cells

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Note that the alu casing is common with the negative terminal of the cell. If in compression it should have some form of insulating material over the flimsy blue plastic coating to ensure that a direct short between 2 series cells does not occur.
Mark, I owe you an apology. My manufacturer confirmed that in the long term it would be best to have 1-2mm epoxy sheet or similar between the cells and at the bottom. The case is positively charged.

So sorry for the doubt.

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Old 25-01-2020, 10:31   #30
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Re: Casing for Aluminum Cells

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Note that the alu casing is common with the negative terminal of the cell. If in compression it should have some form of insulating material over the flimsy blue plastic coating to ensure that a direct short between 2 series cells does not occur.


Are you sure about that? It’s hard to believe since it creates a significantly larger hazard for series cells.
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