Why another spot welder project?Building a spot welder is one of the (arguably few) cases in which you can build something for a fraction of the price of the commercial version with comparable quality. And even if build-before-buy were not a winning strategy, it is a lot of fun!
So I decided to embark on the project, and I looked at how other people have done this. There is literally a ton of interesting information and videos about this on the net, with quite a wide variation in quality of design and build.
The quality of the build that one can realistically achieve depends on the tooling, machines, and facilities available, so it was not surprising to see quite a wide variation on this front. On the other hand, I was not expecting to see that most projects just use a simple manual switch to start and stop the welding process.
In fact, accurate welding time control is key to the quality of your welds, and you can not achieve that by flipping a switch by hand.
I felt that, while building yourself a spot welder is a topic that has been probably beaten to death already, maybe one could make a better machine by using the three-step welding process with accurate timings, as professional machines do. So I gave myself five main design goals for my project:
Support for three-step welding processAccurate and configurable timingsAbility to persistently store and retrieve welding profilesSimplicity of design and buildUse of only commonly available componentsThe result is my 1-2-3 Spot Welder, and in this instructable I will explain the welding process control part of the project. The video and this instructable show pictures of the prototype test welder, before all components are mounted into a proper case.
If you need to familiarize yourself with the concept of resistance welding and how one can make a welder using a microwave transformer, please do so before you read on. I will concentrate of the control of the welder, not on how a welder works or how to build one. I feel this this is well covered elsewhere.”

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