lol It should come with instructions at least… 
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The contact and the coil of your relay is the wrong way around, you will fry the coil of the relay if you do it like that and make a dead short across the battery with the foot switch 
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Glad someone brought this up it seemed wrong to me but then thought I don’t really ever use relays in schematics so maybe it’s just something weird with the schematic, but does make more sense you’d energize the coil to close the switch that completes the circuit for the electrodes.
Ah! Yes you’re right, it should be flipped horizontally! Doh! 
I just did a quick update & demonstration video of my DIY spot welder as I’m just building a pack at the moment…
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I’ve had to do another update video about the welder because I was getting the same questions again and again on YouTube…! Plus I needed to dispel a few myths!
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Hopefully someone is still active 
Would this work with a 12V 120A battery for a 50cc moped?
Need more amps
What he said ^
You need at least 200A
@darkkevind how many spot welds can a NEW car battery do? I have an old used 440 CCA battery which I charged but it stuggling to weld.
My battery is still going after thousands!
You just have to make sure you keep it charged up…