How to hold batteries?

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I have this 270 cell battery I’m making (again) and am worried the crazy glue and welds aren’t strong enough and maybe if I drop the motorcycle cells could come detach or short. I’d like to add an expanding foam that was light and had decent rebound so it doesn’t collapse.

Polyurethane comes in all types of hardness but I fear it will not bend and rebound with physical stress and instead break or collapse.

Silicone expanding foam I can only find in 25a duro or maybe 40a if I want to spend a lot. I think neither is hard enough but it’s flexible and won’t break.

There’s fish paper between cell groups as well as vinyl wrap with plastic o-rings and I’ll add another paper o-ring before I weld it.


What you recommend? I don’t want to glue it to the box so can get it out if need to.
 

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It's going in that clear plastic box, right? I'd recommend using layers of fish paper, and/or fiberglass sheets, and/or thin styrofoam, in an arrangement that has the pack sort of press-fit into the box. I think that it's right to consider what could happen in a crash, but if you're going motorcycle speeds, and get a hit on that box, you're gonna have a bad day no matter what kind of method you use to fit it in the box.

Rather, you should be considering the daily vibrations and stresses that the pack will be subject too. And in that light, making sure the cells have no wiggle room to vibrate out of their spot welds is more important.

I used a combination of styrofoam and thin rubber insulation sheets on my pack.
 
It's going in that clear plastic box, right? I'd recommend using layers of fish paper, and/or fiberglass sheets, and/or thin styrofoam, in an arrangement that has the pack sort of press-fit into the box. I think that it's right to consider what could happen in a crash, but if you're going motorcycle speeds, and get a hit on that box, you're gonna have a bad day no matter what kind of method you use to fit it in the box.

Rather, you should be considering the daily vibrations and stresses that the pack will be subject too. And in that light, making sure the cells have no wiggle room to vibrate out of their spot welds is more important.

I used a combination of styrofoam and thin rubber insulation sheets on my pack.
Yea going in the clear plastic box


I think it would be a help with sheets of foam but expanding foam would be ideal in filling all voids, if I can just find the right one.

I could pot it all in a solid resin, maybe the hardest silicone I can find (like 50a), but be more weight. It’s a tight fit already and not much added weight really so leaning that way.
 
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You mean you'd install the battery in the box, then use that sort of spray expanding foam? I think that'd be more of a mess than its worth, if you every need to remove it for service.
 
You mean you'd install the battery in the box, then use that sort of spray expanding foam? I think that'd be more of a mess than its worth, if you every need to remove it for service.
I’d pour the foam or whatever while the battery is in the box with a layer of Saran Wrap glued to the box with Vaseline so could possibly get it back out. I’m more worried about safety than the possible need to service. Removing a cell from this battery would be a nightmare anyway with the crazy glue and welding.
 
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If you were to build a house, would you use elements like 2x6" lumber, 4x8' plywood panels, and concrete blocks? Or would you use dice, dominoes, playing cards? Let's be clear: either way can get the job done. But one way opens up a big can of unnecessary problems, and amounts to playing games.

When you use battery elements that are scaled incorrectly for the job, you make problems for yourself that you wouldn't otherwise have.
 
If you were to build a house, would you use elements like 2x6" lumber, 4x8' plywood panels, and concrete blocks? Or would you use dice, dominoes, playing cards? Let's be clear: either way can get the job done. But one way opens up a big can of unnecessary problems, and amounts to playing games.

When you use battery elements that are scaled incorrectly for the job, you make problems for yourself that you wouldn't otherwise have.
What are u saying exactly? What’s incorrectly scaled?

As I have the battery built so far it’s stacked densely, with fish paper strips between groups, krazy glued, and then it would just be the welds and glue holding it together. Maybe u can over-stack cells like this. Maybe the rows are best oriented horizontally by series or parallel. Maybe I should squirt glue down all the holes.

Even the hardest 40a silicone foam is too soft to support the cells. The benefit of silicone being great rebound and won’t crack but it’s too soft and needs to be pretty hard and that’s only polyurethane.

I’ll be squeezing the samples at the local seller soon: https://www.smooth-on.com/tb/files/FOAM-IT_SERIES_TB.pdf

I think I want it hard, but not so hard it could crack in a hit.



Why not?

It would easily waterproof it, maybe suck off a bit of heat. ..wouldn’t the foam absorb more heat if it’s black? Not that it has anywhere to go in a kevlar wrapped plastic box.



Just some other brand stuff.


 
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Well, using 270 cells to make a battery that isn't 270S is one clue.
It would be appreciated if you told what you’re thinking instead of clues. 270s…in series?! It’s 30s. I haven’t put the copper/nickel on yet. It’s in a pic above.
 
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If you were to build a house, would you use elements like 2x6" lumber, 4x8' plywood panels, and concrete blocks? Or would you use dice, dominoes, playing cards? Let's be clear: either way can get the job done. But one way opens up a big can of unnecessary problems, and amounts to playing games.
[...]
The can is open, worms everywhere.... How do I phrase this politely? Here we go: Who in their right mind would consider using wooden posts and plywood to build a permanent house, for actual people to live in? It's a cheap way to build houses, so more people can afford one, which is a totally worthy goal, but one look at a picture of tornado or landslide damage should tell you that this building method (very common in the US) has serious down sides. So I don't think that is a good example or analogy for building a sturdy crash proof motorcycle battery enclosure.

For the OP:
You can get pourable/castable polyurethane in about any hardness you want. I've used it in the past for cast gas tight seals, and it performed reasonably well even at low temperatures. But I would suggest doing away with the glue and foam, reducing the cell density a little bit, and rebuilding your battery using commercial cell holders, like this one:
1718605239377.png

Keeping the cells a little bit apart would also allow some space for a cooling fluid, should it turn out to be needed.

For impact protecting, you could consider sheets of so-called non-newtonian rubber, like the material used for motorcycle personal protective gear pads. It is relatively soft when subject to slow deformation, but hardens on impact. These sheets would go between the outer hard shell (metal, ABS, other sturdy plastics or composites) and the battery pack. An example: 4mm Solid Skived D3O® AERO Sheet (10" x 14.5") | Order 4mm D3O® Sheets - Gamebreaker
 
It would be appreciated if you told what you’re thinking instead of clues. 270s…in series?! It’s 30s. I haven’t put the copper/nickel on yet. It’s in a pic above.
Chalo doesn't like packs made from 18650s, that's all.
 
Chalo doesn't like packs made from 18650s, that's all.
I think 18650 cells are great for making packs in the 1500 mAh to 3500 mAh range.

I think using 9P construction instead of 1P is literally manufacturing trouble for yourself. But evidently some folks like trouble more than I do.
 
i think anyone who builds a pack of 200 or so 18650s doesnt like it anymore. So many connections can fail in so many ways, better to have everything fogured out before starting the buid. For my smaller batteries i found nice waterproof plastic boxes (general purpose enclosures for electric stuff) plus lining of foamed PVC boards. But it was for 80 cells, for 200 it wouldnt be strong enough.
 
giant packs of small cells are the norm. Using small cells is unavoidably if you want to use high power/energy cells that are available. I think I read that when cells get bigger they lose ability to shed heat and can’t be as powerful.


The non-Newtonian foam seems best. Wish I could find a pourable expanding foam version. I’ll likely end up using polyurethane instead when I can’t find any.
 
I think I read that when cells get bigger they lose ability to shed heat and can’t be as powerful.

When wee cells are ganged up and stuck together with high resistance nickel, they make a lot of heat that doesn't even happen when you use a cell format that fits what you're doing with it.

When you have hundreds and hundreds of homemade spot welds tying your pack together, you will have failures, and those failures will tend to cascade consequent problems through the pack.

Building a high capacity, high power battery the easy way, with top quality cells, is actually a lot cheaper than using suspect hobby type cells, now that there's a waste and surplus stream of automotive modules available. If you can use the intact modules, you can even benefit from automotive quality packaging that beats anything you could possibly build for yourself.

Why would someone build a motorcycle battery with the same cells and techniques you'd use for a small RC car? Most often, I think it's only resistance to learning something new, with a dash of monkey-see, monkey-do mixed in.
 
Why would someone build a motorcycle battery with the same cells and techniques you'd use for a small RC car
I'll share my reasons, for my 840-cell pack. They're not everybody's reasons, they're very specific to me, but since you asked, I can answer.

-Cost of cells for the user is low, mine were $.70 shipped, making it $62/kwh for cells alone. Total pack cost including nickel, holders and cabling at roughly $70/kwh. BatteryHookup advertises their comparable "deals" for $80-100/kwh, usually raw cells only.
-I used secondhand cells from dead scooter packs presumed dead, so I kept lithium out of a landfill.
-I use 18650s for my DIY home battery storage, so I will have a third use for the cells after they age, further keeping them out of a landfill.
-Cylindrical cells don't need compression.
-Designing pack size and shape is easily scalable and customizable when using small units, less so when using large square prismatics.
-I designed the pack to only require max 10A per cell connection, this is easily achievable with copper-nickel sandwich. My real-world draw, now that I have it in use, maxes out at 5A per cell, for a couple seconds. Voltage drop is negligible, and I'm not even using power cells.
-I have lots of practice spot welding, I'm good at it, and I have lots of dead cells hanging around that I can use to calibrate my spot welder settings before I make the main pack.
-Aesthetics. I think they look good, my battery case is clear, so I get to see all my perfectly aligned rows and stacks of hundreds of cells every time I go for a ride. That's a benefit for me, and I don't get that serotonin from seeing packs made out of rectangles.

None of your cons for 18650 packs are overtly wrong. Just that the pros outweigh the cons, for me personally, and perhaps for others.
 
How about designing and printing (either yourself or via a service) Nylon cell holders to constrain your cells in your desired pattern? It sounds like you have saved enough from other aspects of the build to accommodate an extra cost, especially if it will satisfy your aesthetic and practical safety considerations.. Then fitting in the box may become simpler as you may only need to wedge/secure the cell holders and not the whole bulk..

(Yes its a black art.. but a youtube of 2x preteen kids explaining how to design a basic box probably scripted by a parent.. was enough basic building blocks to get me started with Tinkercad, might be worth a sit down with a cup of coffee and checking out??)
Though thinking about it these days if you can think of it someone has done it before so a trawl of the sites like thingiverse will probably get you cell holders in every config going ;)
 
Building a high capacity, high power battery the easy way, with top quality cells, is actually a lot cheaper than using suspect hobby type cells,
These are new molicel 42b cells. Good stuff.



I like those cell holders and should’ve used them but I’m not taking this battery apart and would take hours and lots of bucks in new vinyl n plastic o-rings. I think the battery is fine as long as I can pot it in something stiff n tough. I’ll be using expanding polyurethane foam of some unknown duro unless someone dissuades me.
 
The problem with the foam is not that it wouldn't work, after all that's what's inside a tesla battery pack, some fancy foam but having tried to use such foams for things like this, the chance you get it to work on the first shot is the issue. Most likely you'll get a mess with something that is not filled as much as you would like but to just fill the space between the cells and box might have a good chance of filling nicely but anything not covered in some form or release film will be permanent.

If it were me I would first constrain the cells to each other better, so for instance gluing some fiberglass sheet in between and on the ends of the stacks. I would probably also strap the cells together with some amount of preload to keep them compressed together, which is another solution to your concerns of wanting the foam to be stiff enough. I would probably do this with a printed cage that went around just the outside exposed cells and then outside of that I would strap them all together with some kevlar line using a versatackle knot to provide the preload. The printed cage could be improvised in other ways as well like some fiberglass for instance. Then you can use some foam either expanding or sheet to keep it in place inside the battery box.
 
Gluing them all together, even if you get the perfect fill with something that is low enough viscosity to fill all cavities, also means you lose the ability to rework the whole pack when (inevitably?) some fraction of cells go bad over time.
Yes, it is a lot of work to take what you have apart, but that's just how R&D goes; much better to go in small steps and improve the details before committing all your cells irretrievably. If you are really hell bent on casting/foaming, I would at least do some test casts with tightly packed cylindrical objects (cut up broom stick or dowel).
 
Gluing them all together, even if you get the perfect fill with something that is low enough viscosity to fill all cavities, also means you lose the ability to rework the whole pack when (inevitably?) some fraction of cells go bad over time.
Yes, it is a lot of work to take what you have apart, but that's just how R&D goes; much better to go in small steps and improve the details before committing all your cells irretrievably. If you are really hell bent on casting/foaming, I would at least do some test casts with tightly packed cylindrical objects (cut up broom stick or dowel).
Cutting the foam is easy.


I can pour the foam in sections to make sure gets fully filled.
 
I’d pour the foam or whatever while the battery is in the box with a layer of Saran Wrap glued to the box with Vaseline so could possibly get it back out. I’m more worried about safety than the possible need to service. Removing a cell from this battery would be a nightmare anyway with the crazy glue and welding.
The expanding foam works and a number of companies do it. I feel like it's got some fire-stop properties as well in terms of insulating from physical contact, and perhaps acting as a sort of fire break between cells.
However, the second I saw the idea for expanding foam I began to get nervous. It's a good idea, except for the fact that the stuff is nearly impossible to remove. I've gotten a few used but nice downtube (sorta shark style) e bike batteries that have expanding foam injected in between the outer-most case and the inner-case which also acts as a battery holder where on the outside perimeter the case encloses the cells. The cell terminal ends have a central circle exposed and looks like a typical cell-holder frame, and between the battery cell bodies body (inside the "honeycomb". cell is a homophone here- battery cell and cell as in a delineated space) cell chamber has maybe 2 cm along the vertical axis of the 18650 cell exposed. The expanding foam which gets injected and expands to fill gaps works it's way inbetween the battery cells insulation and the plastic frame of the cell holding it.
This makes it a HORRIBLE pain to disassemble.

saran wrap, or maybe coating the cell sides in some vaseline will prevent the PU foam from adhering since there are no solvents I've found that can defeat it and I can't just go digging into the pack with a metal tool since that will short the cells.
 
When wee cells are ganged up and stuck together with high resistance nickel, they make a lot of heat that doesn't even happen when you use a cell format that fits what you're doing with it.

When you have hundreds and hundreds of homemade spot welds tying your pack together, you will have failures, and those failures will tend to cascade consequent problems through the pack.

Building a high capacity, high power battery the easy way, with top quality cells, is actually a lot cheaper than using suspect hobby type cells, now that there's a waste and surplus stream of automotive modules available. If you can use the intact modules, you can even benefit from automotive quality packaging that beats anything you could possibly build for yourself.

Why would someone build a motorcycle battery with the same cells and techniques you'd use for a small RC car? Most often, I think it's only resistance to learning something new, with a dash of monkey-see, monkey-do mixed in.
This seems like a pretty wild way of ignoring the advice of most of the industry. Your logic falls apart when you consider you could replace "small RC car" with "every Tesla on the road".
 
This seems like a pretty wild way of ignoring the advice of most of the industry. Your logic falls apart when you consider you could replace "small RC car" with "every Tesla on the road".
Tesla has battery building robots working in near clean room conditions with laser, ultrasonic or whatever other kind of cell welding that nobody here uses. Also in case you hadn't noticed, they have upsized their cells at least twice in spite of the technical advantages they enjoy in assembling them.

I'll note that almost all the other, more established and proven players in the automotive space use much larger formats, when they could easily use lipstick cells if they wanted to.
 
What’s a bigger cell that would work well on a motorcycle? A year ago was comparing lifepo4 cells n weights on batteryhookup and the 26650 a123 was best. And powerful. I think everyone wants bigger cells of course and safer, easier.. where are they?



 
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