DIY Ebike Battery Build

In this video, I show complete instructions on how to build your own lightweight in-frame e-mountain bike battery. The battery is for my CEF50 lightweight carbon ebike (see previous build video here: • Bafang M820 DIY Lightw... ) and it shaves 5lbs off the total weight, bringing it down to just under 40lbs! The specs are 36v, 10S2P, 360Wh, 3.7lbs.
Here is a list of the parts and tools I used to build it.
- 20 x Samsung 50E 21700 5000mAh 9.8A Battery cells. I got them from www.18650batterystore.com
- Spot welder s.click.aliexpress.com/e/_Dkr...
- 10S Battery BMS s.click.aliexpress.com/e/_Dlx...
- Heat shrink wrap s.click.aliexpress.com/e/_DDW...
- Grid nickel strips s.click.aliexpress.com/e/_Dka...
- Straight nickel strips s.click.aliexpress.com/e/_Ddb...
This is the wiring diagram for the battery pack: drive.google.com/file/d/1mAqj...
3d printer files can be found here: www.thingiverse.com/thing:647...

[@ficorama]

Hello. nice bike, and great assembly video. what is the range with a 10s2p battery?

[@TheLekkir]

Hi. Have you gathered more experience? What can you say about the performance of the engine - would you choose it again? how noisy is it? does the engine cope with occasional stronger climbs of 16-20%? and how does it cope with continuous climbs of 6-16% what range/hill climbs did you manage to cover on the smaller and on the larger battery? By the way, very nice piece you came out with :)

[@pedrosaobento3328]

30A bms on 20A continuous battery?

[@08gong]

Excellent build, thanks for sharing! May I know the purpose of the file named "battery case spacer"? It seems not present in your video guide. And again, we all wait for your coming videos about your rides!

[@dualincomenokids4712]

That spacer goes on the inside end of the case. This DIY case is shorter than the factory battery so in order to fit the frame mounting holes I had to make this case a bit longer than the batteries themselves

[@08gong]

@@dualincomenokids4712I see, how thoughtful!

[@dew1352]

DINK, thanks for this. Would it be possible to share the wire schematic, if you have it, or, a link to where I can find it, please?

[@dualincomenokids4712]

I've a added a link in the video description to the wiring diagram for the battery pack

[@08gong]

Hi! Is it possible to increase the thickness say to 2mm, for better safety?

[@dualincomenokids4712]

It's a real tight fit between the battery and frame. You could probably make the walls 1mm or so thicker but it may require a bit more effort to slide the battery into the frame. But I think since it sits inside the frame, the way the thickness is now should be study/safe enough. But you could try making it thicker

[@08gong]

@@dualincomenokids4712 I asked this because my printer shop can't handle thickness below 2mm... that stops me trying to start the project.

[@08gong]

@@dualincomenokids4712 I trust your design is sturdy enough / safe.

[@24ecko]

Don't you need vents on the battery case?

[@dualincomenokids4712]

My understanding is lithium ion batteries don't need venting. More importantly is the cells need to be spaced so they don't touch and are protected from impacts and water ingress. The OEM battery from this frame is 100% sealed. Also, the BMS I used has a temperature sensor which is attached to the cells and provides overheating shut down. So I think it's a pretty safe design

[@Durwood71]

Just remember, when it comes to do-it-yourself rechargeable batteries, if you do a single thing wrong, you could create a very bad situation. Even factory made batteries have been known to catch fire, and they burn with extreme destructive energy. Source: Tesla

[@dualincomenokids4712]

Agreed... I am super paranoid when it comes to battery quality and charging. For my build I made sure to use high quality cells from a reputable supplier. I then took a lot of time and triple checked things at all steps of the build. Because of this, I am more confident in the quality of this battery than many commercial offerings (especially cheap stuff of unknown origin). Lithium ion batteries have risks... I take precautions with all my batteries, but there will always be chances of fires etc. as we see in the media

[@HappyAchterhooker]

Please know that 3d prints are NOT waterproof. Water will get in between the layerlines and seep trough.

[@dualincomenokids4712]

Excellent point... I should have elaborated the point that the seal is water resistant and the case itself will resist splashes but should not be exposed to water if possible. Emtb's in general should not be submerged in water. The battery is somewhat protected from water being inside the frame but water can definitely seep in from the headset and certainly from the motor area. I am conscious not to ride through deep water, use pressure washer to clean the bike etc. I you are more susceptible to these things, this case can be made more water resistant by coating it in epoxy resin etc. to seal up the layer lines. Also I didn't mention it, but the filament used to 3D print should be carefully selected. I used PETG which has better thermal properties but also better water resistance

[@MrSupermugen]

I've printed plenty of Wee jet boat hulls, They dont leak at all when new.. , however after some time of thashing them they end up leaking, we now seal the hulls with a paint we got from the local paint shop, its like a resin paint, been excellent.