I made a battery box for my LiFePO4 battery pack using Carbon Fiber Material - Page 1
Forum section: electronics / beginners

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: November 11, 2021, 03:43:30 pm
content: And now I realize that using Carbon Fiber material to make things where electrical conductivity matters is a bad idea.Because when Carbon Fiber material is solidified with a hardener such as epoxy resin, it becomes very conductive.https://techiescientist.com/does-carbon-fiber-conduct-electricity/This is something most anyone knowledgeable in electronics and carbon fiber material would probably know. I simply overlooked it.I used 1/2" wood for the 3 vertical frame pieces and 1 large piece for the bottom. They were all wrapped with 2 layers of Caron Fiber material on both sides and coated with Crystal Clear epoxy resin.Anywhere (and everywhere) I passed bolts through the carbon fiber, that became a ground to the wood frame.Conversely, anywhere a metallic bolt was used to secure an electrical device to the frame, it was instantly connected to everything else similarly connected.This became an engineering nightmare and I had to re design quite a bit of the structure to eliminate the grounding effect. This included cutting the holes larger and then using a non conductive liners in some places, the use of insulating nylon washers and the use of nylon bolts instead of metallic bolts as possible.Even after doing all that, it's still not ideal because of the high energy of LiFePO4 batteries and the potential for shorting to the frame.If I had to do it all over, I most certainly would NOT use Carbon Fiber for this type of project. Big mistake.It might make for an attractive LiFePO4 box, but the conductivity of Carbon Fiber makes it not ideal.I posted this so that it might make some one else aware of this situation before investing way too much time in a project like this.After ALL I've done to mitigate this problem, I still find my LiFePO4 pack is draining. Still looking for the source.Carbon Fiber fabric for Electronic devices? Don't do it.These are images from the CAD design. It didn't come out as nice after butchering for this electrical problem and my awful epoxy attempt, so these are easier to see.It was a good idea, with tons of work......that didn't quite go as planned.

author: Ian.M
author_rank: Super Contributor
timestamp: November 11, 2021, 04:24:17 pm
content: Breaking news - Carbon is conductive - Film at 11There's nothing wrong with using carbon fiber for mechanical/structural parts where extreme strength and stiffness is required with minimum mass. Its conductivity is no harder to deal with that that of steel or aluminum in a metal battery box, of which there are millions worldwide e.g. in many UPSes. However using it over wood core is less than desirable, as the core is not dimensionally stable enough to take full advantage of the carbon fiber and is far far heavier than a foam or composite honeycomb core would be.The last time I built battery boxes, they was of glasscloth sheathed plywood with epoxy filleted interior joints glass taped on the outside. The plywood provided most of the strength and the single layer glasscloth sheathing was only there for durability and acid and water resistance.

author: Manul
author_rank: Super Contributor
timestamp: November 11, 2021, 04:29:14 pm
content: My colleague once decided to order carbon fiber enclosures for our RFID readers. I saw first assembled units and my eyes got wide, he was like "what's wrong?" I said "just turn it on". It was not able to read any tags, totally shielded. True story.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: November 11, 2021, 05:18:31 pm
content: Quote from: Ian.M on November 11, 2021, 04:24:17 pmYes it is.And I got the idea from another guy on another forum where countless people proceeded to duplicate his example....all with carbon fiber cloth and epoxy resin.So, this thread isn't for folks like you.It's for folks like me who are electronics hobbyists who like me, might not remember that in the enthusiasm and excitement of doing a project like this.btw...as explained in the linked article......while Carbon is conductive, it's really about carbon fiber sheets.And the article gives the exact conductivity of carbon fiber sheets both before and after epoxy resin is applied.The conductivity before the resin is applied is nearly negligible. After wards, magnitudes more conductive.The information is in the article I linked.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: November 11, 2021, 05:20:17 pm
content: Quote from: Manul on November 11, 2021, 04:29:14 pmBingo!Exactly the point of this thread. It happens. And it doesn't mean the designer was a dummy....just didn't do thorough research or give it enough thought ahead of time.Heck....even with all their billions and teams of engineers....General Motors, Ford, NASA and Microsoft have ALL made colossal mistakes.Thanks