Build thread: nickel strip spot welder from microwave oven transformer
Posted: Wed Apr 10, 2019 2:04 pm
There is a surprising amount of information about using microwave oven transformers to build spot welders appropriate for assembling battery modules, but generally they are crappy YouTube videos that don't include actual schematics or even decent images of the electrical connections. There are also a lot of terrifying lash-ups out there just waiting to start a fire; I'm hoping to share something somewhat less fire-prone.
Lithium cells do not like high temperatures. There are plenty of folks who solder their cells - including me, until now - but I want to start building some "serious" packs (a solar power wall and some additional e-bike batteries), so I need to treat the cells properly.
The "correct" way to connect 18650 cells is using nickel strips and a spot welder. Spot welders are not cheap, but you don't need an automotive-grade welder. A misused microwave oven transformer and a few odds and ends will produce a workable welder; adding some relays and a Raspberry Pi or an Arduino can yield the same results you get from retail welders selling for several hundred bucks.
In this thread, I'll document both builds. First, I'll build the minimal solid-state version of the welder - which will work, but it doesn't work amazingly well. Once I have v1 working, I'll start working on the control circuit for the "intelligent version," and then I'll replace the solid-state parts with the upgraded gizmology.
Lithium cells do not like high temperatures. There are plenty of folks who solder their cells - including me, until now - but I want to start building some "serious" packs (a solar power wall and some additional e-bike batteries), so I need to treat the cells properly.
The "correct" way to connect 18650 cells is using nickel strips and a spot welder. Spot welders are not cheap, but you don't need an automotive-grade welder. A misused microwave oven transformer and a few odds and ends will produce a workable welder; adding some relays and a Raspberry Pi or an Arduino can yield the same results you get from retail welders selling for several hundred bucks.
In this thread, I'll document both builds. First, I'll build the minimal solid-state version of the welder - which will work, but it doesn't work amazingly well. Once I have v1 working, I'll start working on the control circuit for the "intelligent version," and then I'll replace the solid-state parts with the upgraded gizmology.