Do my new blue cells need to be packed together ?

[FilterGuy]

1) Aluminum shell cells need to be insulated from each other for electrical reasons, regardless of the thermal situation.

I had not heard that before (and I am about to deploy some aluminum 'blues'. (I had always used plastic before) Could you point me to information about this?

 

[sajjen]

I love that you ran the numbers. I think you've been very aggressive; I would expect the battery being discussed (RV energy storage, not a traction pack) to operate at well under 1C normally and have much lower heating than your worst-case scenario.

Yes, as you understand, it was meant to be worse than worst case scenario figures for the type of battery we're discussing.

1) Aluminum shell cells need to be insulated from each other for electrical reasons, regardless of the thermal situation. So we are having a somewhat academic debate: especially if the manufacturer provides spacers that allow for an air gap, the air gap is "free" modulo volume concerns in the RV. It would be strange to design a different packaging method that removes that air gap. (Now, I think they design in the gap because many of their packs are used in traction applications, where there will surely be substantially higher heating. But this does not alter the fact that in many cases there will be an established, manufacturer-approved install method that already provides for the gap.)

Aluminium case cells do not have the case electrically connected to any of the poles. There is no need to electrically isolate the cells from each other. Manufacturers of cells do generally not provide any spacers.

2) Your calculation finds a worst-case 28degC increase. I would argue that even a 5degC increase distributed unevenly throughout the battery pack is unacceptable. We know that heating is one of the biggest contributors to aging. We know, empirically, that others with LFP packs experience more cell degradation on the interior cells when they are arranged in rows or grids. In an RV, there likely will be times when the enclosure's ambient air temperature reaches or exceeds 40degC. I would not want the middle of my pack to be a concentrator of whatever heat does accumulate in that case, if I could help it, because the degradation scales nonlinearly with temperature. Does a real pack generate even a 5degC delta in the middle under mild loads? I don't know for sure.

The 28K figures is evenly distributed in the whole pack. That would implicate a theoretical cell with perfectly uniform current distribution and perfect insulation from the environment. In practice, the temperature increase would be much lower, but also nonuniformly spread. Cells in the middle of a pack would indeed see larger temp increases.

3) Your calculation does not account for any ohmic heating at the interconnect. Those can be substantial -- especially once wire, dissimilar metals, mistakes or wear (under-torqued connectors), and especially fuses become involved. All of those potential heating sources can transfer heat right back into the cells if they are in close contact. (My own DC system's total resistance is roughly 25mOhm!)

I've run over 100A through uncoated copper bus bars connected to Winston 3*60Ah cells in a system that had been installed on a boat for several years without me touching the connections. That system had temperature sensing on each cell pack and never noticed any significant differences. YMMV, I guess.

I have personally measured, with a FLIR camera on a single bare aluminum shell cell in open air at room temperature, at 0.25C for about one hour, a gradient of just under 1degC between the middle of the largest exterior face of a cell and its outer edges. I could easily imagine that becoming five or ten times that when densely packed with little convective opportunity. I haven't done any more analysis, because, well, see #1 above. But I think it is too early in our understanding of how this chemistry behaves in the long tail to simply dismiss outright possible heating issues in a large battery pack operating at lower rates. Yes, the heat here is second-order compared to a traction application... but some of us are trying to baby these cells and stretch well into the many thousands of cycles that it looks like this chemistry can deliver, under ideal conditions. Why risk it by introducing suboptimal conditions?

I maintain that I would not worry about cooling in the circumstances we're discussing. I guess I simply feel it's worth the risk?

 

[nebster]

I had not heard that before (and I am about to deploy some aluminum 'blues'. (I had always used plastic before) Could you point me to information about this?

The hard data is scant at best. I don't think you will find find a spec sheet that says "our cells don't have perfectly isolated shells." What you will find, instead, is that many manufacturers sell them with spacers. Or, if you contact their reps, they'll indicate that the blue plastic is there to provide electrical insulation, but that adding more is a good idea.

There were a few anecdotes of issues with leakage over time in old posts on an EV message board, but I don't have them for reference.

Contact your manufacturer's rep and ask them what they recommend, though.

 

[nebster]

Aluminium case cells do not have the case electrically connected to any of the poles. There is no need to electrically isolate the cells from each other. Manufacturers of cells do generally not provide any spacers.

Incorrect. Many manufacturers provide spacers, or specify that you should isolate them yourselves when asked.

If you do not ask, you may try to count on the flimsy blue plastic they wrap around the aluminum.

The 28K figures is evenly distributed in the whole pack. That would implicate a theoretical cell with perfectly uniform current distribution and perfect insulation from the environment. In practice, the temperature increase would be much lower, but also nonuniformly spread. Cells in the middle of a pack would indeed see larger temp increases.

Yeah, that's the concern. Even pack heating would also lead to some degradation, of course, but imbalanced degradation creates new problems, brings into the picture an active balancing mechanism, etc.

I've run over 100A through uncoated copper bus bars connected to Winston 3*60Ah cells in a system that had been installed on a boat for several years without me touching the connections. That system had temperature sensing on each cell pack and never noticed any significant differences. YMMV, I guess.

Plastic shell cells definitely do not bring the heat to the shell as efficiently as aluminum. You also need a FLIR gun to see small differences; fingers or an IR sensor might not be sensitive enough.

Also 3x60Ah is a pretty small pack. I'm advocating for cooling on a large design with a lot of cells and a lot of heat in what is otherwise essentially one big thermal mass.

Definitely YMMV.

I maintain that I would not worry about cooling in the circumstances we're discussing. I guess I simply feel it's worth the risk?

I mean, see my point #1, this is largely irrelevant for modern al-shell cells that come pre-spaced.

But, sure, it's a tradeoff. Neither you nor I have the hard data to tell which way makes the most sense, and there is more than one right answer. But I think most people building up a new aluminum shell design can afford the extra few cubic millimeters it takes to create the air gaps, and it's cheap insurance.

 

[Aussiecroc]

The guy I bought my cells from who does lots of domestic and commercial installations told me I need to put at least 1mm of extra plastic between the cells in case the blue plastic wears off from movement of the RV. He was quite serious about this. Any more gap and the connect bars that I got today from him won't fit the thread holes on the terminal. So the thick aluminium cell connect bars negate my earlier questions about gaps.

 

[ghostwriter66]

The guy I bought my cells from who does lots of domestic and commercial installations told me I need to put at least 1mm of extra plastic between the cells in case the blue plastic wears off from movement of the RV. He was quite serious about this. Any more gap and the connect bars that I got today from him won't fit the thread holes on the terminal. So the thick aluminium cell connect bars negate my earlier questions about gaps.

The issue is that if you put the aluminum LFP batteries together without spacers and snug them down with each other -- then they will in fact NOT rub but move as a single unit - if that makes sense... We do NOT put spacers in between our aluminum batteries and have not had a problem -- and they are on numerous trailers that are banged around all day ... as long as you make sure that movement between the batteries are at a minimum I see no issues ...

 

[Aussiecroc]

Thanks so much for your help

 

[sajjen]

Incorrect. Many manufacturers provide spacers, or specify that you should isolate them yourselves when asked.

I've only seen spacers provided by resellers, never by cell manufacturers. But I can not prove a negative. Please show us where you've seen this.

If you do not ask, you may try to count on the flimsy blue plastic they wrap around the aluminum.

If your cells move around enough, relative to each other, to chafe the (very thin) plastic cover, I would say you've failed in securing the cells. They should be secure enough to not move. Not because of chafe, but to not put physical strain on the terminals.

Plastic shell cells definitely do not bring the heat to the shell as efficiently as aluminum. You also need a FLIR gun to see small differences; fingers or an IR sensor might not be sensitive enough.

Also 3x60Ah is a pretty small pack. I'm advocating for cooling on a large design with a lot of cells and a lot of heat in what is otherwise essentially one big thermal mass.

Definitely YMMV.

To clarify, it was a 3P16S pack. The temp sensors were permanently mounted, thermally connected to the terminals, should be the hottest part of the exterior of a plastic cell.

I mean, see my point #1, this is largely irrelevant for modern al-shell cells that come pre-spaced.

You need to show where you find your "pre-spaced" cells.

 

[nebster]

I've only seen spacers provided by resellers, never by cell manufacturers. But I can not prove a negative. Please show us where you've seen this.

Just start shopping for aluminum shell cells and you'll see a bunch of variations on the spacer theme today. You can shop domestically on ECPC or on alibaba. You can read a long thread about this where we just re-hashed all this same stuff on cruiser forum. Or, you can watch Will's video of the "Fortune" cells and witness some spacers in action.

The distinction between reseller and manufacturer is less clear than your earlier statements lay out. My manufacturer has several discrete facilities and warehouses the cells in Shenzhen. They have "inside reps" who sell exclusively their product, but they also work with a variety of resellers/brokers. And, of course, some domestic shops import their cells and relabel/mark them up.

I worked directly with the exclusive rep in SZ when I ordered my cells.

If your cells move around enough, relative to each other, to chafe the (very thin) plastic cover, I would say you've failed in securing the cells. They should be secure enough to not move. Not because of chafe, but to not put physical strain on the terminals.

I definitely agree that avoiding putting any mechanical load on the terminals is very important.

I do not agree that I am willing to trust the thin plastic. Even in installation it could be nicked or scraped, and I would have little way to tell until one of my cells starts interacting with its neighbor in some undesirable way, maybe slowly over years. Again: most manufacturers want us to insulate the cells in some way.

To clarify, it was a 3P16S pack. The temp sensors were permanently mounted, thermally connected to the terminals, should be the hottest part of the exterior of a plastic cell.

I really think plastic cells are irrelevant here. They have an inferior density, clearly inferior thermal shedding properties, and they are the "version 1" of LFP. I'm not saying they don't make great batteries -- but I'm also not surprised you don't see much thermal action on the outside of them.

You need to show where you find your "pre-spaced" cells.

I don't need to do anything, but I've tried to present ample evidence above, in the two minutes I'll grant you to write this reply. You should go brush up on the modern offerings. Seriously, send a note to a couple reps and ask them about the insulators. We've already done it, and we already know what they say.

 

[sajjen]

There are plenty of reseller providing spacers, I'm not denying that. Fortune being one of them. I have never seen an actual cell manufacturer selling spacers.

And as to the electrical isolation of cells. Just poke your multimeter probes through the plastic cover and measure to the terminals, there is no connection.

I've worked in the electronics industry in China. There is no such thing as an "exclusive rep". Anyone willing to do the peanut business of selling cells directly to you or me is far, far down the chain of resellers and representatives of the actual manufacturer.

I will leave you to your beliefs, and stay out of this thread.

 

[nebster]

There are plenty of reseller providing spacers, I'm not denying that. Fortune being one of them. I have never seen an actual cell manufacturer selling spacers.

There is no reseller named "Fortune."

And as to the electrical isolation of cells. Just poke your multimeter probes through the plastic cover and measure to the terminals, there is no connection.

I already said above, I don't know the nature of the leakage. I just know that it is purported to exist.

There are, also, aluminum shell cells that have a direct connection between one terminal and the shell. But those are surely the exception.

I've worked in the electronics industry in China. There is no such thing as an "exclusive rep". Anyone willing to do the peanut business of selling cells directly to you or me is far, far down the chain of resellers and representatives of the actual manufacturer.

I will leave you to your beliefs, and stay out of this thread.

Yes, my direct observation contradicts yours. You speak in totalities ("never", "no such thing", "not a problem"). I'm simply showing, again and again it appears, that the world is bigger than your view, and there are many subtleties you have either missed, forgotten, or that you choose to remain ignorant of.

Thanks for your contribution.

 

[nosys70]

"Anyone willing to do the peanut business of selling cells directly to you or me is far, far down the chain of resellers and representatives of the actual manufacturer"
that is why you will not receive advices about how mounting them. These guys are box pusher and and estimate that if you are purchasing such product, you probably have the knowledge on how to use them.
Personally i never seen an electric component that is not properly spaced from the other if possible, so it seems to be a general common sens rule.
i do not see a reason not to apply this commons sens here unless you really need the few lost millimeters.

 

[Steve_S]

I have searched Hi & Lo using all sorts of terms on Amazon, Ebay, Alibaba for Lifepo cell spacers. So if someone has actual links for square LFP cell spacers post them.

 

[nebster]

I have searched Hi & Lo using all sorts of terms on Amazon, Ebay, Alibaba for Lifepo cell spacers. So if someone has actual links for square LFP cell spacers post them.

I think they're pretty tied to the dimensions of a specific cell. I suspect a lot of the pack assemblers have them molded up when they have enough order flow to build a lot of packs. Have you tried contacting whoever sold you the cells and asking them?

 

[Steve_S]

vapourware

 

[nosys70]

or possibly , these cells are mounted on custom made frames, so generic plastic spacer would not be very usefull.
most eletric parts sold in bulk or for insdistrial use do not come with accessories, because the accessorie is usually another product you have to buy.
Even for mounting an electric panel you have to buy each bit separately and use them respecting electrical rules that are not
listed in the product instruction (because they can vary a lot).
I think LFP cells (particularly the big ones) are still considered as industrial equipement. The day you will find them in the supermarket, you can bet there will be tons of accessories availables.

 

[nebster]

or possibly , these cells are mounted on custom made frames, so generic plastic spacer would not be very usefull.

Indeed.

Or, perhaps the manufacturer might be confident enough in their ability to keep the shell from polarizing, such that they don't think any insulating spacing is necessary with their cell.

Or, perhaps the manufacturer might know a lot about the risks of shell polarization but is offloading these cells through a distributor who has no clue. Maybe even intentionally.

Who knows? Pretty hard to say.

 

[nosys70]

there are books about that

Mechanical Design and Packaging of Battery Packs for Electric Vehicles

Safety and reliability are the two key challenges for large-scale electrification of road transport sector. Current Li-ion battery packs are prone to failure due to reasons such as continuous transmission of mechanical vibrations, exposure to high...

link.springer.com

Methods for Durability Testing and Lifetime Estimation of Thermal Interface Materials in Batteries

To ensure sufficient thermal performance within electric vehicle (EV) batteries, thermal interface materials (TIMs), such as pastes or adhesives, are widely used to fill thermally insulating voids between cells and cooling components. However, TIMs are composite materials that are subject to...

www.mdpi.com

 

[patman]

so who actually makes the fortune battery,,, the information in covered into the video that Will did....

 

[FilterGuy]

so who actually makes the fortune battery,,, the information in covered into the video that Will did....

I was not able to learn much by poking around the web. (I did learn that fortune.com is for the magazine). I did come accross this:
https://www.electriccarpartscompany.com/Bright-Star-150Ah-Aluminum-Encased-Battery They seem to have a nearly identical packaging under the name bright star (whoever that is)