Diyspotwelder

Projects
Participants
Skills	Electronics, Metal- and woodworking, Soldering electronics programming
Status	Dormant
Niche	Mechanics
Purpose	Infrastructure

Lately, hackaday et al. have been supplying a number of reviews/buildlogs of DIY spotwelders. They all seem to be based around taking a used/surplus microwave transformer and removing the secondary (highvoltage) core , replacing it with a few turns of thick copper-cable which instead take the power from the primary coil and turns it into low-voltage, high-power.

Current state: We've liberated a transformer from a microwave; removed the secondary coil with a hacksaw. Saved the 'shunts'. It's now stored on a shelf below the 'woodworking-tables', next to the 'printer parts box'.

Meanwhile, Justa has found a nice two-conduit cable, used for supplying -48V power to telco-equipment. They contain 2 conductors, both consisting of 5-6 solid-core copper wires normally used to supply 20A+ each. Total cable-length is around 2meters, supplying up to 4 meters of heavy-duty copper-cable, useful for secondary coil. On one side, the copper cable has been finished with a galvanized-metal ring-lug; possibly to be replaced with a set of 'copper offset clamps' which seem perfect for the job.

The plan:

• Start with a simple test-setup to check if everything works like it should
• Add proper welding-terminals and enclosure
• Make an assembly with spring-loaded clamping system
• Add timing and/or power-control to it
• Add a foot-pedal system to it to allow two-hand operation

Explanation: Making something that has a high power running through it and will fuse some metal together isnt too hard to do, it'd seem. Getting the right cable + terminals seems to be the hardest part of all that.

The next step is to make something that'll leave your hands free to hold your work-piece while you're welding. Something spring-loaded (or rubberbanded) seems just the thing.

Then, the next step is to have something that allows you to first position the welder and only then turn it on for a quick weld. Either a switch or a 'push-through' pedal-system seems the right way to go.

Ontop of all that comes the wish to have some safety built in. A quick way to interrupt the power to prevent a meltdown, or even simply an automatic timing system that cuts off by itself. A feedback on the amount of power running through the welder is perhaps also great. An arduino with a sense-loop + a timer... connected to an SSR; seems just the thing.

Then, having that in place, the next step could be to use the SSR and some smart software to do PWM-based power modulation; see 'design references'.

References:

• https://www.youtube.com/watch?v=vrlvqib94xQ - Handheld spotwelder design
• http://www.instructables.com/id/How-to-Make-a-Spot-Welder-for-Cheap/ - Instrucable page belonging to video above.
• https://www.youtube.com/watch?v=hTaGa93lOGU - How to modify the transformer
• http://hackaday.com/2014/07/21/spot-welder-dont-buy-it-build-it/ - the/a hackaday article.

Design references:

• http://electronicdesign.com/power/novel-pc-compatible-ac-power-controller-uses-solid-state-relay - How to use an SSR to do high-power PWM control