Building a Portable Solar-Powered Spot Welder: Nearly Practical!

Last time, we covered storing and charging a 3000 Farad supercapacitor to build a solar-powered, portable spot welder. Since then, I’ve made some improvements to the charging circuit and gotten it running. To recap, the charger uses a DC-DC buck converter to convert a range of DC voltages down to 2.6 V. It can supply a maximum of 5 A though, and the supercapacitor will draw more than that if allowed to.

Capacitor charge current decreases with time as the capacitor charges. Source: Hyperphysics

After some failed attempts, I had solved that by passing the buck converter output through a salvaged power MOSFET. A spare NodeMCU module provided pulse width modulated output that switched the MOSFET on for controlled periods of time to limit the charging current. That was fine, but a constant-voltage charger really isn’t the right way to load up a capacitor. Because the capacitor plates build up a voltage as it charges, the current output from a constant-voltage charger is high initially, but drops to a very low rate in the end.

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Building a Portable Solar Powered Spot Welder: Charging Supercapacitors

Before Lunar New Year, I had ordered two 3000 F, 2.7 V supercapacitors from China for about $4 each. I don’t actually remember why, but they arrived (unexpectedly) just before the holiday.

Supercapacitors (often called ultracapacitors) fill a niche somewhere between rechargeable lithium cells and ordinary capacitors. Ordinary capacitors have a low energy density, but a high power density: they can store and release energy very quickly. Lithium cells store a lot of energy, but charge and discharge at a comparatively low rate. By weight, supercapacitors store on the order of ten times less energy than lithium cells, and can deliver something like ten times lower power than capacitors.

Overall they’re an odd technology. Despite enthusiastic news coverage, they are a poor replacement for batteries or capacitors, but their long lifespan and moderate energy and power density make them suitable for some neat applications in their own right. Notably, they’re used in energy harvesting, regenerative braking, to extend the life of or replace automotive lead-acid batteries, and to retain data in some types of memory. You’re not likely to power your laptop with supercapacitors.

Anyway, I had a week-long holiday, and two large capacitors of dubious origin. Sometimes we live in the best of all possible worlds. Continue reading “Building a Portable Solar Powered Spot Welder: Charging Supercapacitors”

The Nicest Home Made Spot Welder We’ve Ever Seen

By golly, look at the build quality of this homemade spot welder.

Just about everyone on here knows it’s quite possible to build one of these things using a re-wrapped microwave transformer, but they’re usually made of wood like the one we swap on Friday, and we often wonder how much real use they get other than “hey look I built a spot welder!”. I myself made one, but then ended up buying a professional one because it works better. Not [Matthew Borgatti] though, his looks better and has more features than even the one I bought!


Why? Because he put some serious thought into his design. He even 3D modeled the whole thing in SolidWorks.

Beyond the excellent laser cut enclosure (complete with ratcheting work piece clamping), [Matt’s] also added an Arduino to create a timing circuit. Most times you just squeeze the clamp, press the button, and watch the metal heat up — “I think that’s good…”

But with an actual timing circuit you can calculate how much time you need versus current and electrode size to produce a good quality weld.

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Joining Sheet Metal Together with a DIY Spot Welder

Once in a while there comes a time that you need a tool for one specific job. In these cases, it doesn’t make much sense to buy an expensive tool to use just once or twice. For most of us, Spot Welders would fall into this category. [mrjohngoh] had the need to join two pieces of sheet metal. Instead of purchasing a commercial unit, he set out to make his own spot welder.

spotwelder A spot welder works by passing an electric current through two thin pieces of metal. The resistance of the metal work pieces and the current passed though them creates enough heat to melt and join the two together at a single spot. To be able to get the high current needed for this project, [mrjohngoh] started with an old microwave transformer. He removed the standard secondary coil and re-wrapped it with 1cm thick wiring to get maximum current out of the transformer. The ends of the coil wire attach to electrodes, which are made from a high-current electrical plug. The electrodes are mounted at the ends of a pair of hinged arms. The weld is made when the two pieces of metal are sandwiched between the electrodes and power is applied.

Spot welding isn’t just for joining two pieces of sheet metal. It’s also used for things like welding tabs onto battery terminals. The versatility and easy of building these welders make them one of the most featured tool hack we’ve ever seen.

A Professional Spot Welder Made out of a Microwave Transformer

Spot welders are one of the very few pieces of metal working equipment that are actually very much cheaper to build yourself than to buy commercially. In fact, between salvaging a transformer out of an old microwave and buying some of the other components, it’s doable for under $100USD in most cases.

We’ve shared this hack quite a few times before, but [Albert van Dalen] has really taken the cake on creating a very detailed and extensive guide to not only building his, but how to properly use it for various purposes.

[Albert] designed it in a way that allows it to be configured in both opposed and series electrode positions which means besides being able to spot weld sheet metal together, you can also spot weld battery tabs while on cells!

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Spot Welder; Don’t Buy It, Build It

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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