Originally Posted by 18650battery
i am planning to spot weld about 60 3ahr cells in parallel to make a 3.7V 180Ahr cell and then series connect these to make a 120V pack with a BMS for each 180Ahr unit.
anyone done anything similar and can give me any good tips?
Been there, done that.
We used 26650 A123 M1 cells to make PHEV packs to convert Prius from HEV to PHEV.
The mechanical design is what will come back to bite you.
- Be prepared to pay $ 8 K to $ 25 K and 3 months of labor just for the set-up (not including cells). I am not exaggerating!
- Put a lot of thought in the design of the battery block and the complete battery
- Use a hexagonal pattern
- You'll need a fixture shaped just right to squeeze the cells together
- Glue the cells together with Elmers Glue or the like, into a block
- Make yourself a mask, to physically prevent you from unintentionally shorting across cells where you don't mean to
- Get an honest to goodness cell welder (no soldering)
- Build a table for the welder. Use rollers to help you shift the battery block in place
- Get nickel sheets (5 to 10 mils) and cut them to shape, to create your electrodes
- Have an expert set the welding profile for your cells and your nickel plate
- Practice, practice practice welding cells before you start on a real block
- Design an enclosure for the battery blocks: isolated, yet sturdy
- Use flexible connection between battery blocks (for example, braid strap)
- Add fuses rated for the full pack voltage, to blow in case you short across a block or misconnect blocks during battery pack assembly.
The BMS is easy:
- Option 1: lots of wires: use a non-distributed BMS, such as the Orion BMS, outside the battery
- Option 2: lots of ell boards: use a distributed BMS, such as the Lithiumate, inside the battery. These cell boards are exactly the right size for 18650 cells, and fit in the nook between 2 adjacent cells, so they take no extra space.