3D printing 21700 holders with petg?

[syntony]

Is anyone using petg holders in their ebikes? Im affraid it will break too easy if i crash. Prints are strong after printing but my experience is they get brittle over time, also winter doesnt help.

I want to make 2kwh battery so it will be pretty big and need to hold a lot of weight. So my question is:
Should i print it or just better buy holders that are holding together on tiny piece of plastic?

 

[harrisonpatm]

Scan through my two builds in my signature. I've used 3dprinting extensively, in dozens of spots. But not for the cell holders directly, for a simple reason: it's just cheaper to buy them. They're widely available in lots of configurations.

I used PETG, PCTG, CFPETG, TPU, GFPETG, PA6-CF, depending on what part im printing.

 

[syntony]

Scan through my two builds in my signature. I've used 3dprinting extensively, in dozens of spots. But not for the cell holders directly, for a simple reason: it's just cheaper to buy them. They're widely available in lots of configurations.

I used PETG, PCTG, CFPETG, TPU, GFPETG, PA6-CF, depending on what part im printing.

But did you crash on it? My actual battery are li-pols in aluminum square profile, and they survived like 10 serious crashes already (including falling like 5meters of stairs). I have doubts about average holders that are connected with 2mm plastic pieces...

 

[harrisonpatm]

But did you crash on it?

Yep, car hit me at lower speeds

 

[syntony]

Yep, car hit me at lower speeds

seems like your battery survived. Its well made. Transparent desing really helps in visual inspections after crash

 

[amberwolf]

My actual battery are li-pols in aluminum square profile

If you have non-can-style cells, either pouch or in rectangular / prismatic casings, they should be in a compression fixture with their largest flat surfaces mated to each other.

Check the cell spec sheet for the compression psi required by the cells.

Fixture can look like this, or several other types.

 

[syntony]

If you have non-can-style cells, either pouch or in rectangular / prismatic casings, they should be in a compression fixture with their largest flat surfaces mated to each other.

Check the cell spec sheet for the compression psi required by the cells.

Fixture can look like this, or several other types.

Those are turnigy hardcase and dont need compression, im using them almost everyday for like 10-12 years, cant remember

 

[scianiac]

In terms of crash resistance I think the whole design of the battery pack is more important than the cell holders, that is if the outer case of the battery is strong and well supported the cell holders won't be under much stress even at high G forces because they will all be compressively loaded evenly into the case. So you want to make sure the outer case is strong and/or mounted to the frame well. And perhaps more importantly you want to make sure the cell stack is mounted well to the case in all axis. That mounting doesn't even have to be solid per-se as long as it's even across the whole pack.

Material wise I have to agree every time I've tested PETG it seems too brittle but also seems to have crack propagation issues. That is if you flex it in the wrong way, even if it's not an impact, with too much stress concentration will cause it to crack catastrophically through the whole part and not just deform and spread the load through the surrounding material. For most things I use ABS as it has pretty good properties all around including very good impact properties. It's far from the strongest but has a good balance of properties and is inexpensive. You can also solvent weld it together to form larger structures and at least with the cells I tried you can solvent weld it to the cell sleeves too.

 

[syntony]

In terms of crash resistance I think the whole design of the battery pack is more important than the cell holders, that is if the outer case of the battery is strong and well supported the cell holders won't be under much stress even at high G forces because they will all be compressively loaded evenly into the case. So you want to make sure the outer case is strong and/or mounted to the frame well. And perhaps more importantly you want to make sure the cell stack is mounted well to the case in all axis. That mounting doesn't even have to be solid per-se as long as it's even across the whole pack.

Material wise I have to agree every time I've tested PETG it seems too brittle but also seems to have crack propagation issues. That is if you flex it in the wrong way, even if it's not an impact, with too much stress concentration will cause it to crack catastrophically through the whole part and not just deform and spread the load through the surrounding material. For most things I use ABS as it has pretty good properties all around including very good impact properties. It's far from the strongest but has a good balance of properties and is inexpensive. You can also solvent weld it together to form larger structures and at least with the cells I tried you can solvent weld it to the cell sleeves too.

I think you are right, outer case is very important. I might use same aluminium 100x100 mm profile, but not sure yet because it will fit only 64 21700 cells and my plan was to fit 100 of them. For holders i think i will also change my plan and wont use 3d printer. I will just make it on cnc machine at my workplace, probably from hdpe abs or pe1000.

 

[byke]

I'd buy holders because it's convenient and they're pretty cheap, but with 3DP parts if the pack is built well with layers of fiber tape and cushion around it, it's probably not coming apart. If it did, it'd probably be a scenario where the entire bike is essentially garbage.

 

[Chalo]

3D filament printing is to 2020s white males what hot glue was to 1990s white females. Once they learn how to use it, that's the only method they use for anything, regardless of suitability.

It's useful. But please keep in mind that the spat-out-by-wasps version of any material is without exception the least impressive version of that material.

 

[scianiac]

3D filament printing is to 2020s white males what hot glue was to 1990s white females. Once they learn how to use it, that's the only method they use for anything, regardless of suitability.

It's useful. But please keep in mind that the spat-out-by-wasps version of any material is without exception the least impressive version of that material.

While I disagree with some of that you also aren't totally wrong. As with everything it's in the details, yes I 3D print like everything but that is because it is the most suitable usually down to cost, time, flexibility, design constraints and when it's not I machine it, laser cut it, fabricate it etc.

The issue is like anything else you have to understand what you are doing, which honestly when it comes to mechanical parts probably 99% of people with a 3D printer have no idea. I can design a strong enough and lighter part quickly and print it quickly and cheaply because I understand where the material will be weaker because it's printed, how to print to minimize those, how different materials behave and how to design for 3D printing.

 

[byke]

White seems to be pretty important component to the formula, maybe there's some variability there?

Also, anyone in the RC airplane world has been digging hot glue nonstop for decades.