Mate X battery 52V 15Ah – diy with 21700 cells
DIY 52 V 15 Ah e-bike battery for the Mate X: 42 × 21700 cells (14S3P) in the original enclosure, no BMS, two 7S blocks, 3D-printed cell holders (STL).
This quick post aims to detail the build of a 52v 15000mAh battery fitting in the aluminium enclosure of the Mate X.
This battery pack features 42 x 21700 cells (5000mAh) x 3 (parallel) x 14 (series).
One choice I made was to trash the BMS: remove a SPoF (Single Point of Failure), my previous original battery pack was killed by the stupid BMS (fully drained cells) and you get pretty angry when you discover 65×18650 cells dead because of a 20$ board failure.
I simply split the 14 cells series in two blocks of 7s which will be easy to charge with a classic external RC lipo/liion battery charger. Simple and less parts will be exposed to the bike vibrations.
Total cost for components under 200 Euros ($240)
- 42 x BAK N21700CG 5000mAh: 3.90 Euros
- new aluminium enclosure (if you are not reusing the original Mate X): ~30Euros
- 2 x balancing 7s cable: 5 Euros
Material and tools if you don’t already have:
- Charger Li-Ion >=7S: ~50 Eur
- Spot welding machine: ~12 Eur
- Silicon cable and nickel sheet plate: 10 Eur
- 3d printer… and ABS filament.
BAK N21700CG cells rocks. 5000mAh is the top of the line and it’s a well-known high quality brand which aims to clone Samsung cells. Every cell I received where all precisely charged with a maximum difference of 5mV between them, impressive.
The 21700 cell holder I designed is a perfect fit. I used ABS for the printing material.
📎 cell-end
The cell holder features 11 slots allowing 4 stacks: 11 | 10 | 10 | 11 cells like this:
The assembly (very ugly picture 😉 sorry)
Operational: >50 Volts
Balancing cables: 2 x 7s
Packing and isolation: epoxy plates and isolation foam which allows to compress make the packs tight and secured:
One half:
Charging, some time later… of course you can charge both half with two charger and upgrade the PSU to allow fast charging (I am limiting at 2Amps because I have a poor 65w psu in front of my 1000w ISDT T8)
