18650/21700 Case Material?

[Ham]

The resin, so I am advised, will turn softer and much more pliable in a thermal run away event and thus not be an issue for venting.

your normal 2 part resin you buy at your local store will not do that.

please dont forget that the resin does not give you structural strength and adds a considerable amount of weight wich still needs to be supported and needs more shock absorbing materials and so on. its a circle that just adds more problems then solutions.

most people that think they need resin simply dont. its like the "fuse wire" BS that pops up constantly. people think they need "fuse wire" to protect cells when its just something they saw tesla do and want to copy it. completly ignoring it that its not even fuse wire in tesla packs. its just the cheapest and fastest way to have a robot make thousands of battery connections an hour. i talked to tesla people and they simply stopped correcting people when they kept calling it fuse wire.

Thanks Flippy,

How does it not add structural strength, that seems counter intuitive?

I am not sure what type of resin the builder uses but I have a sample and have been advised to pop it in boiling water to see how much softer it becomes. I’ll have a play this afternoon I think just for interest.

The grin drop tests seemed to show significant cell protection in potted vs unpotted from a non builder perspective but am happy to be educated if there is something missing from my perception of that?

The weight element does seem like a negative, agreed. I am not sure how much weight penalty there is on a 70 cell pack. Part of me wants as light as possible, the other part of me thinks worrying about an extra 500g to a kg on an ebike is silly.

Have you ever seen inside a levo or other brand pack too see how they make them so weather and shock proof, I’d love to see inside of one?

 

[Ham]

Thanks Ian, that is a hefty pack at 15kg! Good to know the case is a good heat sink too

 

[flippy]

How does it not add structural strength, that seems counter intuitive?

you make a large, flat surface (aka: a piece of paper) of resin and expect it to be structural. that is not how it works. thin sheets of resin are very flexible in all the wrong directions. you are aksing the resin to absorb forces in the exact opposite direction it needs to. that creates cracks over time wich get mustiure in the pack and you are done at that point. the pack will rust and destroy itself from within.

I am not sure what type of resin the builder uses but I have a sample and have been advised to pop it in boiling water to see how much softer it becomes. I’ll have a play this afternoon I think just for interest.

boiling water is different then holding a blowtorch to it and setting of a firecracker. apples-oranges.

The grin drop tests seemed to show significant cell protection in potted vs unpotted from a non builder perspective but am happy to be educated if there is something missing from my perception of that?

its a party piece. it does not give real life performance. how often to you plan to drop your bike from 10ft on hard concrete with the battery first?
there is a difference between a crash test and driving a car 250k. you can make a REALLY safe car but its kinda useless if the body cracks apart after 20k.

Have you ever seen inside a levo or other brand pack too see how they make them so weather and shock proof, I’d love to see inside of one?

no, i dont have to. the building practices are nearly the same.

i fail to see how your use case warrant potting the battery. there are vastly more secure ways in making a battery durable.

 

[Ham]

Do you have any build threads showing how?

 

[flippy]

Do you have any build threads showing how?

no, i dont. i do commision jobs for single commision requests. and i dont share how i build my larger industrial batteries for obvious reasons.

i am here to help people along in their DIY stuff and teach people the basics and does-donts.

 

[Ham]

That's a shame. It's hard to visualise how your packs could protect the cells and connections as well as potting (a picture is worth a thousand words) but I guess we'll have to imagine harder this time.

Thanks for your input though in this thread.

 

[flippy]

its not that hard to imagine the tape i linked to, the foil i mentioned and a tactical and liberal application of closed cell foam. :wink:

 

[Ham]

Perhaps but I feel a thing is easier to imagine once you have seen it already, as you have Sir. Thanks anyway I do appreciate your experience shared.

 

[flippy]

Perhaps but I feel a thing is easier to imagine once you have seen it already, as you have Sir. Thanks anyway I do appreciate your experience shared.

just read carefully and use common sense. it will get you pretty far. if you make a mistake you learn from it. you don learn to ride a bike by looking at someone else doing it. :wink:

 

[Ham]

thanks again

 

[jpc6000]

A case made of carbon. Is that not good and strong material for battery case?

 

[flippy]

A case made of carbon. Is that not good and strong material for battery case?

there is zero advantages to do so. unless your main issue is having too much money.

 

[TrotterBob]

A case made of carbon. Is that not good and strong material for battery case?

On the plus side its very lightweight and strong. On the minus side its conductive. Just scratch the epoxy surface of carbon fiber and once you hit the actual carbon strands they are almost as conductive as copper.

Machining carbon fiber requires protective gear. At the very least a good face mask, not the silly ones we wore for covid, but an N95 or better. Keeping the carbon dust off of your skin is highly adviseable too. Best to dremel in the great outdoors as that stuff can go everywhere.

 

[jonescg]

i tested bunch of setups triggering a ptc with a 2 part epoxy on the cell. the results were....violent.

Got video? I'd love to see it.

 

[flippy]

Got video? I'd love to see it.

sadly not.

 

[jpc6000]

Mine back battery pack is made of alluminium that is also conductive, and only two heatshrink folie away from battery.


I want made two cases, one for in the bike frame and one for back pack.

21700 cells.
For Backrack I use 10P x 21S, I have made the case.
Aluminium, carbon, plastic or 3D printing.