Spot Welder; Don’t Buy It, Build It

Spot Welder

Spot welders are super handy for making sheet metal enclosures for your projects. The problem is, commercial ones are rather expensive… The good news is, they’re actually really easy to make! This is [Caio Paulucci's] first submission to Hack a Day, and it was a weekend project him and his father just finished.

A spot welder works by dissipating large amounts of heat in between two electrodes in the material you are bonding. It makes use of a transformer that converts mains voltage to a very low voltage, but high current energy source. The cool thing with this type of welder is it’s perfectly safe to hold onto the electrodes as the voltage is so low, you won’t get electrocuted. By running a super high current (generally >1000A @ ~1-2V) through a small surface area, you can super heat most materials hot enough to weld them together.

They can be made using the transformer from a microwave, some heavy duty welding wire (generally 2/0 or thicker), and a few other odds and ends such as wood, electrodes, and maybe a few nuts and bolts. At the most basic level, you are basically re-wrapping the transformer’s secondary coils to change the ratio to produce a low voltage, high current transformer.

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An autonomous boat across the Atlantic


While we may be waiting for unmanned drones to deliver a pizza, there’s already an unmanned ship plying the Atlantic on a transoceanic voyage. It’s called Scout, and it’s the product of about two years worth of work by a very close-knit group of friends.

Scout is a 12.5 foot ship constructed out of foam and carbon fiber loaded up with solar panels, electronics, an electric motor and a SPOT satellite tracker. The team has been working on Scout for the last two years now, and this last week the autonomous ship finally set out on its mission: a 3500 mile journey from Rhode Island across the Atlantic to Spain.

Right now, Scout is just over four days into its mission having travelled 90 miles from Rhode Island on its way to Spain. You can follow Scout on its journey on this very cool live tracking site.

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DIY spot welder makes metalwork easy

At Hackaday, we’ve seen enclosures built out of just about every material. From wood, glass, epoxy resin, plastic, and even paper, all these different types of enclosures provide some interesting properties. Sometimes, though, you need an enclosure made out of metal and welding together steel cases isn’t exactly easy or cheap. [manekinen] came up with a really great solution to the problem of welding together sheet metal. It’s a very easy to build spot welder perfect for fabbing steel cases.

The core of the build is a transformer pulled from a Technics stereo amplifier. [manekinen] removed the stock secondary winding and rewound the transformer four turns of 35mm ² wire (about 2 AWG). This made the transformer put out 2.6 Volts a 1 kA – more than enough to weld 22 ga sheet.

For the control mechanism, [manekinen] put a limit switch on the electrode arm and wired that to a timer. A knob on the front of the welder allows him to vary the time the welder is on from 0 seconds to 4 seconds.

The results are fantastic – trying to rip apart a weld only results in the metal itself tearing; exactly what you want to see in a welder. It’s a great build made even more fantastic by the welder building its own enclosure.

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Capacitive discharge spot welder update


It seems one of our commenters took great umbrage with [PodeCoet] not documenting his capacitive discharge cutting properly. [PodeCoet] had been waiting till he got the full spot welder working before publishing, but he’s expedited the work after all our whining. Check out his full writeup of the device in its current state. It uses a 1Farad audio cap for storage. A dsPIC monitors all of the voltage sources and regulates charging. A nice touch is the tactile switch on the electrode.

How-to: Build your own spot welder

Welding stainless steel

Spot welders are used in the fabrication of automobiles, PC cases, power supplies, microwave ovens, electrical junction boxes, Faraday cages, and various electronics. A spot welder is used because it produces a highly defined point of contact weld. The materials are welded without excessive heating, so working pieces are handled easily. The weld is also highly controlled and repeatable. In this how-to we cover the basics of a spot welder, and then show you how to build one from a microwave oven transformer.

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