I decided to throw out the old battery cage and start again. There were a few reasons for this decision, but the main two were build quality and design. The build quality was not great as I was learning to weld while assembling it. Secondly, the design was less than ideal as I didn’t really plan anything out and it wasn’t an efficient use of the space. The old design also didn’t leave a hug amount of clearance under the bike which was a little concerning.
I decided to build a new battery cage around the ideal layout of the battery cells instead of ideal layout of the frame on the bike. This will make assembly, reliability, and maintenance of the battery pack a lot better. The design includes 4x 6s45p battery modules. Each battery module will slot in from the side, making it easy to insert or remove a module if necessary. There is also enough space for the BMS and a few bus bars to connect each module together. The entire frame is built out of steel RHS, and steel sheet to enclose everything. There will be a hinged door on one side, allowing easy access for maintenance.
In the photos below, you can see each slot, and the included foam padding. This foam padding ensures each battery module is a little cushioned and isn’t rubbing/vibrating directly against the steel frame or sheet. This should also help reduce the chances of any weld joints coming loose from vibrations. I put some acrylic spacers with foam on top, and laser cut some large sections out of it in order to save some weight as acrylic is pretty heavy. The bottom acrylic/foam spacer only has a few mm of space around it and is not glued or attached. It’s held in place by friction from each slot’s guide rail.
Each module will contain about 270 18650 cells and be wrapped in some insulating wrap with kapton tape for extra protection. You can see in the photo below what the spacing is like with some “dummy” modules I made. These were made using some of the actual cell holders and cells that will be used in the modules so I can get an accurate idea of the spacing and fit.
Comments 2
19/01/2022 at 8:27 pm
One thing I wonder if you have considered. The engine was a big chunk of alloy, that made a solid connection between the upper mount (that leans on the steering post) and the bottom bracket. You've replaced it with an open collapsible aluminium box. Are you not worried that the bending forces of the rider weight are now taken entirely by the frame top tubes? I'm thinking of what happens on any kind of jump, and what might happen with a front impact that bends the top mounting of the steering tube. Both might cause distortion of the battery enclosure, and hence a fire risk.
I wonder if constructing the battery pack around a central strut linking the mounts might be safer.
Best of luck!
31/01/2022 at 1:42 pm
Thanks for the comment! The battery box is made out of steel RHS with with the aluminium sheet all around it. For now it should be more than strong enough, but before getting it road worthy I intend on reinforcing it a bit more just to be safe. It uses the previous engine mounting points, so as long as it's a similar strength to the old engine, it shouldn't be an issue. Part of the process of getting it roadworthy is to get an engineering signoff; so I'll mention it to the engineer and see what they say.