Discussion - Cases for aluminum cells

[Turd Furguson]

We all talk about buying cells & testing, but not final assembly

How are you assembling to survive mobile/marine/harsh environments?

 

[Frank in Thailand]

My harsh environment, rural Isaan Thailand..

As they don't move, I simply group them with duct tape and they go inside ventilated cabinet.
The cabinet is in air conditioned room, and locked.
ventilation holes are protected with fine mesh, and temperature sensitive ventilator to make active ventilation if needed.

I don't see the added value to make extra casing around the already cased pouches, (the aluminium outside is casing)

 

[BiduleOhm]

I don't see the added value to make extra casing around the already cased pouches, (the aluminium outside is casing)

Lithium cells tend to expand a little bit at high SoC (and to contract a little when at low SoC) so if they are touching each other they will put stress on the terminals (even on a stationary pack) and that can damage the cells.

To answer the original question I'd say the best solution is to make a very solid pack and mount it with some rubber bushings to absorbe the vehicle vibrations and shocks.

 

[Frank in Thailand]

I don't agree.
Slightly.... Yes, very slightly, like minimal, to be neglected.

(Unless you place +16 cells in one long line)

A very solid pack?? Why?
If you build it with low SoC it expands and push your pack beyond holding limit or expand via the vent?

If you build it at high SoC, it contract, having the same movement as without solid pack.

Or it doesn't really expand and contract that much.
The connections are only at the top, making it possible for the pack to expand like bellows.
The stress on the connections is minimal.

Or, you place all the cells with flexible patch between them, the patch will absorb the expansion and fill up the gap after contraction.

A thin layer of tempex would do the trick.

The aluminium housing is quite strong.

And if there is movement large enough to put stress on the connections..
A strong case will not hold it.

You can split rocks with expanding water...

for me, it's in a cabinet, not moving.
Having a mm tick tempex between them probably never hurts.
I doubt if it will benefit.

 

[BiduleOhm]

Slightly.... Yes, very slightly, like minimal, to be neglected.

More than 1 % against something as rigid as a busbar is not to be neglected to me. Especially as with cycling comes metal fatigue and work hardening.

A very solid pack?? Why?
If you build it with low SoC it expands and push your pack beyond holding limit or expand via the vent?

If you build it at high SoC, it contract, having the same movement as without solid pack.

Because you don't want shocks and vibrations to move one cell relative to another one.

If you use spacers on the periphery but not on the middle of the cells you can have a very rigid assembly and leave the cells enough space to expand at the same time.

 

[Frank in Thailand]

Yes, in case of vibration, you are right.

The topic starter @Turd Furguson , asks how we, personally, do the installation for our personal harsh environment.

My personal harsh environment have no vibration, or it must be an earthquake.

If you use spacers on the periphery, the movement is still the same .
For first (middle) cell, 1% is not much space, but at the 5th cell, you talk about 5 * 1%
And the force of 5*1% that puts stress on the connections.

A busbar is relative rigid, but can easily bend a little.
Making it curve a little
Like bellows of accordeon.

The busbar is the closed part, the cells expanded.

If you try to have top and bottom expand both the same amount (by putting it in a case) there is a lot of force on the busbar and each connection!

We talk about minimal movement here.
Probably the outsides lift 1mm

Trying to make a busbar 1 mm longer takes a lot of force, while bending it for 1mm...
That's easy.

Nice discussion, except I'm quite positive that the people who make the cells are aware of this behaviour of the pouches inside the aluminium housing.
I even expect that they made the products connection strong enough or flexible enough (hence the plastic ring around the poles) to handle this behaviour.

For different environment then my own (not the start question), especially where there is vibration and/ or abrupt movement, yes, very solid pack, with spacers on the bottom and periphery to absorb most of the vibrations.
For that reason.
Not for expansion and contraction.

 

[Will Prowse]

My recent solution to expansion of cells is to use a longer than necessary busbar. This allows for space between the cells. But it depends on the cells. Older cells seem to expand a lot more than the aluminum cased ones, but I am going by anecdotal evidence from cell returns. I don't have data to substantiate my claim.

 

[Frank in Thailand]

If there is space between the cells, adding a spacer like small tempex or rubber foam could avoid the cells from moving if there is vibration or other movement.

I know from old defective pouches that they expand, a lot, in the center.
New ones....
I can try.
Place my 16 cells in 1 long line.
I need to do bottom balance when the BMS arrives.
Then recharge.
One cell is 5 cm. That makes 80cm
1% = 0.8 cm.
Something that should be easy to measure.
(Just put marks on the floor where the cells stand on. If they expand, the marking line should no longer be visible)

If I still can see the marking lines...
The expansion of the new aluminium cased ones are minimal to none.

Fun to test!

 

[BiduleOhm]

My personal harsh environment have no vibration, or it must be an earthquake.

So that's not a harsh environment.

If you use spacers on the periphery, the movement is still the same .

No, because the cell tend to expand only in the middle, a bit like a pillow, it can't strech the sides but it can inflate the large sides in the middle.

For first (middle) cell, 1% is not much space, but at the 5th cell, you talk about 5 * 1%
And the force of 5*1% that puts stress on the connections.

That would be 5 % of 500 % so still 1 %. And each busbar will see the same strain as there's one busbar per cell, it's not cumulative.

Trying to make a busbar 1 mm longer takes a lot of force, while bending it for 1mm...
That's easy.

I don't know what busbar you use but 3 or 4 mm by 20 to 25 mm of copper isn't easy to bend. And even if they are easy to bend, copper and aluminium work harden so sooner or later they will break, especially if you add heat cycles in the equation.

For example: https://bicycles.stackexchange.com/...rs-an-aluminium-frame-lasts-in-a-touring-bike and if you want more technical info on the subject https://www.quora.com/Why-does-alum...a-certain-threshold/answer/Robert-McDaniels-5 and https://en.wikipedia.org/wiki/Fatigue_(material)

If there is space between the cells, adding a spacer like small tempex or rubber foam could avoid the cells from moving if there is vibration or other movement.

Foam isn't rigid enough. What you want is the cells act as one block that doesn't deform under external stress, and remove said external stress as much as possible (and here foam and rubber are very welcome).

Fun to test!

Curious to see the result

 

[Frank in Thailand]

Excuse me?
Only fibrations and shocks are harsh environment??

If that is your honest opinion, please visit Thailand this hot season month, and tell me if you still think that only movement is harsh.

Heat, dust, high humidity, bugs, rodents, lizards, geckos, insects more types and bigger size you have ever thought possible.

After having more equipment burn out in a few years then in my entire life in the Netherlands.. (that is +/- 40 years )
This is a harsh environment.

I never ever have had the pleasure of finding an ants nest in my printer/ copier after 1 week.

And while the ants didn't do direct damage, all the junk they brought to their nest did.
It kept working for a few weeks till it stopped.
And yes, I cleaned as good as possible even with pressurised air.

Heat???

I'm not sure what you are planning to do with your batteries, I can tell you that during charge and discharge the busbars will rise (if any) only 1 or 2 degrees.
No problems there

Inside the housing...

Here is where we should start.
Yes, there is inside the housing room for the pouch to expand and contract.
The aluminium housing is strong enough to not expand en contract with the pouches.
One of the reason they are vacuum inside.

As the housing is made to have the expansion and contraction of the cells, the whole discussion about metal fatigue and stress of the bus bars is just your personal panic.


Never the less, I will do the load balancing, and discharge.
And while I'm at it, why not place a marker on the floor?

I'm 99.9% sure the cells won't move.
And even if they would, the busbar will simply bend a little.
Something it can do for centuries before it will show any signs of wear.
And even then...
It is not on high load, it simply connect cells on a solid base.
No stress, no additional forces.

80 cm long copper bar of 2 or 3 mm tick bend a whole 0.1 cm on the end?
Easy. Really.

Put both tips on an edge.
Please a weight in the center.
Probably 10kg will be enough to bend this little.
Gravity is a bitch.
And coper is flexible material.

Back to your electric off road dirt bike . (joke)
Yes bumping up and down, jumping of cliffs, high vibrations...

It is normal common sense to strap anything as tight and strong as possible.
Not only batteries, also wires (moving copper), and all parts that can possibly go lose. Use loc-tight on all the screws, nuts and so.

But for me that is not more harsh environment then rural Isaan Thailand.

If you have never been here, you don't know and should not make judgements about it.

If you want anyone to judge, it should be the topic starter who asked about our personal installations in our personal harsh environment.

Not generally harsh environment, your personal experience.
How did you do it.
Pictures or it didn't happen

 

[Deleted member 4428]

One of the reason they are vacuum inside.

Where did you learn this?

 

[Frank in Thailand]

Where did you learn this?

Good question!

I saw in a YouTube video some one disassemble aluminium cased lifepo4 cell.

When he opened he could hear the air flow in.

He asked the manufacturer and they told that all cells where made like this.


Sadly only "hear-say"

And I'm really cracking my head about when I saw that video....
When I remember I should be able to come up with a link of that video...

 

[upnorthandpersonal]

You could use a braided bus bar like this:

 

[Deleted member 4428]

I've seen several Lithium cells opened up on YT, but no AL cased cells. Here is a CALB cell being opened.

 

[BiduleOhm]

Only fibrations and shocks are harsh environment??

No, never said that, but shocks and vibrations are a lot harsher than having the batteries sitting on a shelf...

What I consider harsh environment is anything with vibrations/shocks and/or high temperatures (40+ °C) and/or high humidity (90+ %) and/or high differential temperature cycling and/or high differential humidity cycling.

Boats have pretty much all of that.

If that is your honest opinion, please visit Thailand this hot season month, and tell me if you still think that only movement is harsh.

I have been, and it barely qualify as harsh for electronics, unconfortable for humans isn't the same as harsh for electronics.

Heat, dust, high humidity, bugs, rodents, lizards, geckos, insects more types and bigger size you have ever thought possible.

You must be kidding me... pretty much every country has rodent and bugs and the very simple defense is a close environment, like a cabinet instead of open shelves. Heat and humidity here are barely harsh. Dust is everywhere on the planet too and unless it's conductive dust then electronics don't care.

After having more equipment burn out in a few years then in my entire life in the Netherlands.. (that is +/- 40 years )
This is a harsh environment.

That's because consumer electronics are junkier and junkier each year; half of it don't even respect their advertised limits and the other half will break too even if operated in the consumer temperature range (0-50 °C)

Also, if you use grid power I bet it's far from the cleanest in Thailand (yep, I've seen this in reality and it's even scarier than in photo...) so it can be a factor too.

Never the less, I will do the load balancing, and discharge.
And while I'm at it, why not place a marker on the floor?

Yep, I agree.

I'm 99.9% sure the cells won't move.
And even if they would, the busbar will simply bend a little.
Something it can do for centuries before it will show any signs of wear.
And even then...
It is not on high load, it simply connect cells on a solid base.
No stress, no additional forces.

What I'm worried about is less the busbars as they are pretty cheap and easily replacable, it's more the cells terminals.

Why not just leave a few mm between the cells ? that's very simple, cost about nothing and solves any problem related to cells expanding.

Here is where we should start.
Yes, there is inside the housing room for the pouch to expand and contract.
The aluminium housing is strong enough to not expand en contract with the pouches.
One of the reason they are vacuum inside.

Didn't opened one but I bet the aluminium is maximum 1 mm thick and as it's a flat surface it doesn't take much to deform it. If it was a cylinder or a sphere then, yes, it would be 100 times stronger.

Also there's no vacuum inside (maybe a slight pressure differential but that's all) because if it was the case then the cell housing would collapse on itself.

80 cm long copper bar of 2 or 3 mm tick bend a whole 0.1 cm on the end?
Easy. Really.

So you have 80 cm between each cell? try again with a 8 cm busbar and tell me how much you can bend it by hand.

But for me that is not more harsh environment then rural Isaan Thailand.

I guess you never been on boat on the sea, because otherwise you'll know what harsh means.

If you have never been here, you don't know and should not make judgements about it.

If you want anyone to judge, it should be the topic starter who asked about our personal installations in our personal harsh environment.

Not generally harsh environment, your personal experience.

I have been in Thailand, so yeah...

And not my personal experience, the industry defines harsh environments pretty well (because we need to know exactly what to expect to design a product accordingly), for example: https://www.twi-global.com/technica...harsh-environment-in-electronics-or-photonics and my definition is even gentler than theirs, so yeah, Thailand is definitely not a harsh environment for electronics.

You could use a braided bus bar like this:

Yep, that's ideal. I think I'll use this solution for a mobile pack (a 12 V one so 3 busbars, so additional cost isn't really a problem) but for my stationnary 48 V packs I guess it'll be too expensive and relatively useless, just leaving some space between cells is plenty enough.

 

[Deleted member 4428]

Search for forum user M

Trying to make a busbar 1 mm longer takes a lot of force, while bending it for 1mm...
That's easy.

That would depend on the buss bar. I have 1"w x 1/8"t buss bar that won't flex 1mm in that short of a distance.

 

[Frank in Thailand]

"We all talk about buying cells & testing, but not final assembly

How are you assembling to survive mobile/marine/harsh environments?"

Harsh environment according to that list is :
"Could also be understood as an environment for which an entity was not intended"

And a bunch specifications for spaceships.
For temperature above 125c lol..
I'm not sure about what type of products they talk about there,for sure not solar and batteries!!!

The part of "not intended"..
Yes.

Like I wrote, I never ever had my printer/copier with an ants nest before.
Big difference between Rural off-grid Isaan BKK or beach...

While even the coast area is standard harsh.
You don't have to believe me.
Just look at the state of the cars on the sea coast. Older cars.
Compare those to inland.
Sea salt (carried by the wind) is harsh on any (most) metal.
Include electronic devices.

Anyways...
Question was : What are you doing for your hash environment.

Sure, + 45 Celcius is not harsh according to your specifications,but it will kill your lead acid battery in a few weeks.

Who is to decide what is harsh?
Or what is electronics for that matter.
A lead acid battery clearly aren't according to the list.
Even Lifepo4 cells aren't electronics.
They need to withstand at least 125c
Only 125c and more is harsh environment according to that list.
(Or -50)

sea isn't harsh according to the list.
Unless you make gentle waves harsh..
Lol (joking here. Sea with the salt and the water drops, shaking, bumping.
I could say water drops are all over the globe. It's not that it's not on other locations, but the intensity and combination)

Best definition probably is
"anything that makes it decades faster then intended by the producer during regular use".

That can be movement, vibration, heat or cold beyond specifications, humidity, or dry (static electricity)
And bugs

I can assure you that most electronic devices will stop functioning way before the harsh spaceship condition's are ever met (+125 Celcius)

Not to mention your own body.

Also accurate is:
"Could also be understood as an environment for which an entity was not intended"

Everything outside specifications.
Temperature in the sun when the shade is 45...
Not nice.
Shaded area without wind...
Way above 45 degrees Celsius.

That makes it harsh environment.
It is outside the specifications of the lifepo4 battery.

And far outside the specifications of my MPPT inverter (max 40 Celcius)

Rodents and dust is everywhere..
Yeah sure. I know.
I'm not talking about a little.... but a lot of it.

How often do you need to clean the air-filters of your car?
We need twice a Month and replace every 3 months.
According to car companies.. that's harsh environment.

Most of my electronic devices don't have air-filters.
And we need to clean then regularly to have normal air cooling.(pressurised air)

When it rains, it rains a lot. With the high temperature comes high humidity..
The clay dust piled up inside become mushy wet clay.
Ever put soft, wet clay inside your inverter? Probably not.
Or can imagine the natural occurrence of having wet clay in your electronics.
I probably don't have to explain what it does to your electronic devices.

How many times a week do you repair electricity? As cables have been eaten?
Yes, we have 16 cats..14 dogs
Still a lot of rodents.

List can go on.
If you live in a city, you don't have this problem.
I never had them in The Netherlands, not even in the small village.
Sometimes a little of it, but never to this extend.
I probably even might react like you do now.. No idea what's it really like.

Mosquito are everywhere.. yes.
During rainy season I give blood at least 300 times a day.
No joking.
Lucky I have little to no reaction.
I don't mind. My wife and family don't even know different.
The rice fields are heaven for them, and the humans who live in the middle are a feast.
For someone who gets itchy easy after one mosquito bite...
Our location for sure is a harsh environment.
A friend of mine probably would need to go to hospital as he have a lot of reaction to bites....

It's not that it's only here...
It's the combination and quantity.


Anyways..
Topic starter did not ask a discussion about what is harsh. (Unless I read wrong)
But what we do when we find it harsh environment.
Our personal installations.
That's my understanding of the topic starter.
What's yours??

@Turd Furguson ..
Please inform us about your intentions of your question.

I read it as "what do you do for your abnormal installation to keep it safe"

@BiduleOhm reads it (so it feels for me) as opertunity to push his idea of harsh environment.
Probably he is building a Mars lander or satellite
(And that's a joke, not sarcasm)

 

[Frank in Thailand]

You write:
Keep a few mm between the cells to "fix" the expansion and contraction problem..
I have this.
But it can not be with your closed case, as it have many room for movement.

also "customer electronics 0-50 degrees Celsius.

logics would be anything that is less or more is harsh.

I've been at sea.
sailboat, not in a storm, but yes, that is different... Like skydiving is.
or airplane or...
many exceptional extreme environment.

Harsh, according to dictionary is unpleasant, unkind, cruel, or more severe than is necessary

harsh

1. unpleasant, unkind, cruel, or more severe than is necessary: 2. too strong…

dictionary.cambridge.org

Extreme environment..

Extreme environment - Wikipedia

en.wikipedia.org

Like in a storm on the sea..
Dessert, tornado, and all kinds of exceptional....
"Nothing" is good enough.
Can you prepare a lifepo4 pack for the pressure that happens with deep sea diving?
I'm not sure.
i know I can't
not deep sea diving or making it safe to use at that pressure.

but....
how many solar installations do deep sea diving?
or sky diving?

or...

My installation still have a lot to endure.
a lot more then 90% of "normal" installations.

For me that is harsh.
not the 0.5% that goes into extremely difficult installation.

you asked about the busbar?

16 cells is about 80 cm.
that is the 152Ah cells.
put them in one parallel string and you have 80 cm.
if you use one busbar for all 16 cells, that will be 80 cm.

even with 16 (each side, total 32) busbar, they are daisy chained, and together still 80 cm.

just place the 2 outside cells 1mm higher.
will the other 14 also be 1 mm lifted??
If not, something is bending!!

Practical science.
Just do it, and tell me what happened.
Do all the cells lift?
With pack of 4 probably.
Pack of 8 already probably not.
16? No way.
The cells are not strapped together, only connect by busbar and standing on the floor.
Please try and show what is happening.

You don't need to make proof with video and Newton meter wrench.
(As the discussion could start that it was not screwed properly)
Simple picture will do

 

[BiduleOhm]

It's getting ridiculous (clay in the inverter? SRSLY?! what are you doing with your equipment?), I'll not waste more of my time.

FYI I live in rural area (it's actually not even a village but a hamlet, ~50 inhabitants) and in the state with the most rain (mm/m²/year) of France, I spent a week in Thailand (Bangkok for a few days and one of the islands (Ko Phai IIRC) for the other half) and I spent two weeks on a boat on the sea, so yep, I know a thing or two about wheather and harsh environments. If you think Thailand land (even the coast) is harsh then it's fine but don't try to convince others it's harsh because they'll laugh. It's certainly not a nice environment but it's not harsh either.

 

[Deleted member 4428]

What I'm worried about is less the busbars as they are pretty cheap and easily replacable, it's more the cells terminals.

My biggest concern is the cell terminals as well. I am seriously considering LF280 in my Promaster van as a house battery and stationary in my grid tie system. I want to use one brand of the same capacity @ 48v for both. I'm very interested in where this thread goes.

Speaking of threads, the terminal fastener depth is usually very shallow in these types of cells (6mm deep in the LF280). Many postings on other threads in this forum are not concerned about this and I respect their opinions and experience very much. mndare is a open water sail boat captain off the west coast of Washington USA and has installed the LF280 in his vessel. Search this forum for him and you will see that he has no worries about the robustness of the AL cell. There are several other members in NZ and Australia that beat the snot out of their vehicles and have had no issues. But, a couple of postings talk about stripped terminal threads. Thing is though, Time. Will the terminals and the internal connections last the cycle life of the battery under these conditions. In my opinion, that is dependent on the robustness of the manufacturing process and the materials used. Speciffically, the terminal, the mounting of the terminal to the cell, and how the plates are fastened to the terminal. None of those can be determined without opening up a cell, or documentation from each manufacturer.

I posted the video of the CALB cell only to have something to compare to.
Look closely at the terminals in the video. They look substantial to me. Then look at how the plates are connected to the terminal. The wafer thin plates are bolted to the terminal. I would think multiple spot welds would be better. Did you see how easily he pealed that plate away from its anchor point.

I could go on but want to make sure the OP is interested in going deeper into the cell construction.