Custom fiberglass / carbon frame battery case

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Tomblarom   10 mW

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Custom fiberglass / carbon frame battery case

Post by Tomblarom » Apr 16 2021 7:05am

Hello there, I'm planning to build my own case to use as much space as possible. I ordered 21700 cellholders and was able to fit 112 cells (14S8P). I'm riding a Bafang G510 + X1 3500W paired with DP-9 18650 14S6P VTC6 in my converted Haibike:

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I want to build an fixed case, that is similar to this case, but can be opened and is still waterproof. The corners can't be sharp, like they are when using plastic or aliminium bending. I want to keep the organic contours of my frame. I know that this case is from elektro-bikes.pl, but they have no hinges nor locks, plus I want to build it myself.

What would you suggest for sealing and as lock mechanism? I thought about using rivets to join body and lid.

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Dauntless   100 GW

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Re: Custom fiberglass / carbon frame battery case

Post by Dauntless » Apr 16 2021 3:15pm

Tomblarom wrote:
Apr 16 2021 7:05am
What would you suggest for sealing and as lock mechanism? I thought about using rivets to join body and lid.
Silicone for the seal. You can just go buy a tube of it, but maybe you don't think that's just the right thing. You want something like the lid of a jar, the ring inside, right? The kind on you car door are for a something that never touches, but you want contact.

If you're familiar with oogoo or sugroo, or the like I may never have heard of, you can mix it up yourself, mold it by hand, 3D print it. Here's a video of guy making his own.

Latches, dang, the surfaces joined can vary so it's too hard to really recommend. If you don't want to wrap a belt around it the edges where you bolt on a latch need to be secure. DON'T get extra resin there, that makes it weaker.

https://www.etsy.com/listing/211227399/ ... metal-lock

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Tomblarom   10 mW

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Re: Custom fiberglass / carbon frame battery case

Post by Tomblarom » Apr 26 2021 10:45am

I went and got myself some styrodur to make the positive model. Next step is making a proper hotwire foam cutter. This soldering iron-version wasn't hot enough.

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For the hinges, I ordered some of them. Easy to unhook the lid, if needed: https://de.aliexpress.com/item/10000000928752.html

As locks, I may use something that latches in and requires a key to open each time. Similar to what you use in van-builds.

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Dauntless   100 GW

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Re: Custom fiberglass / carbon frame battery case

Post by Dauntless » Apr 26 2021 11:30am

Not familiar with Styrodur, you're in Germany? If XPS similar to EPS as I know it yours looks thin enough you don't need the hotwire, which is a skill in itself. You can just take a straight razor can cut pretty deep, or calmly use a hacksaw blade. Having an edge guide on each side the same as with hotwire is a big help.

https://www.swaylocks.com/forum

Here's where they'll help you learn to shape foam. They periodically have posts on making your own hotwire cutter and the like, there's a search. And they of course do fiberglas. Keep in mind that polyester or vinylester resin for fiberglas will melt your styrene plastic on contact. Epoxy won't. There are still ways to use them together, I'm sure that's somewhere on that board.

https://www.swaylocks.com/search/site/hotwire%20cutter
Any sufficiently advanced technology is INDISTINGUISHABLE FROM MAGIC!
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Tomblarom   10 mW

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Re: Custom fiberglass / carbon frame battery case

Post by Tomblarom » May 03 2021 8:28am

I bought 10m roving fabric (300g/m²) which is basically GFK in a roving pattern, epoxy resin and black color. I hope to imitate the black finish, a carbon surface has, with it. I assume, that I need 1m² for each layer (body + lid). Doing 4-5 layers.

Yes styrodur is XPS, but it's not that easy and clean to cut. Initially I wanted to avoid the mess through using saws, but after a few attempts with hot-wire it seems easier.

One XPS sheet is 4cm thick and the case has to have at least 7cm, since the cells are going to be 21700 (70mm). I wasn't able to glue two halfs together.. Tried it with hotglue, special plastic glue and silicone. My hotglue gun was too weak, the plastic glue melted and dissolved the halfs.. And silicone wasn't able to dry all the way through.. Going to try epoxy.

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E-HP   10 MW

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Re: Custom fiberglass / carbon frame battery case

Post by E-HP » May 03 2021 8:38am

Tomblarom wrote:
May 03 2021 8:28am
Going to try epoxy.
Just make sure the epoxy you are using isn't conductive, if you're using for your battery pack. A lot of epoxies are fortified with metal (steel, silver, copper, etc.) in order to provide greater strength (doesn't compress/deform), but that also makes them conductive.

Tomblarom   10 mW

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Re: Custom fiberglass / carbon frame battery case

Post by Tomblarom » May 03 2021 9:03am

Good point. Going to check that, even though I doubt it. :) Going to wrap the cell packs anyways in plastic GFK plates and heat-shrink.

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Chalo   100 GW

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Re: Custom fiberglass / carbon frame battery case

Post by Chalo » May 03 2021 1:38pm

E-HP wrote:
May 03 2021 8:38am
A lot of epoxies are fortified with metal (steel, silver, copper, etc.) in order to provide greater strength (doesn't compress/deform), but that also makes them conductive.
I know of no metal filled thermal or structural epoxies that are conductive. Even silver filled thermal paste is generally not electrically conductive. The conductive filler does make some such products significantly capacitive, though.
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E-HP   10 MW

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Re: Custom fiberglass / carbon frame battery case

Post by E-HP » May 03 2021 9:31pm

Chalo wrote:
May 03 2021 1:38pm
E-HP wrote:
May 03 2021 8:38am
A lot of epoxies are fortified with metal (steel, silver, copper, etc.) in order to provide greater strength (doesn't compress/deform), but that also makes them conductive.
I know of no metal filled thermal or structural epoxies that are conductive. Even silver filled thermal paste is generally not electrically conductive. The conductive filler does make some such products significantly capacitive, though.
I was thinking Devcon, but there are others. Silver, copper, or carbon filled offer the most conductivity.
https://www.adhesivesmag.com/articles/8 ... -solders-1
https://forum.digikey.com/t/conductive-epoxy/4340
https://www.permabond.com/resource-cent ... adhesives/

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