13/05/2026
Preparing our new BMS boards for our new battery cells’ 12mm terminal bolts - the 123/SmartBMS boards come with 8mm terminal bolt holes. The instructions say “can be drilled out for larger terminal bolts”.
Not as easy to do as for them to write. First of all, these are PCBs with lots of delicate wiring and components, so care needs to be taken with static and general handling. Second, hand drilling isn’t going to be accurate enough. Third, our 12mm drill bit (biggest we’ve got on board) isn’t going to make a hole big enough.
Fortunately, the workshop next to us has a big drill press. We borrowed a 13mm drill bit, but that was still too small. We had to drive into town to buy a 14mm drill bit - but of course no one had one. Fortunately, we found a 9/16” drill bit, 14.2mm.
After securing a PCB with a couple of screws (the boards have two holes just for that purpose it seems) on a wooden mounting board covered with a rubber sheet, I centred the drill press and drilled. Not a lot of pressure needed, just two thin sheets of copper and a thin fibreglass board. But very jagged.
So then used a round file to smooth out the copper. Darn, not quite centred on a few. Surely good enough, still lots of copper area on the battery cell terminals.
