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!

He’s also used an Arduino to allow for precise timing of current application, and created an adjustable force guide to provide pressure during the weld — a feature usually only seen on the commercial units. His blog has tons of information on it, so if you’re interested in building your own, check it out!

[via Reddit]

39 thoughts on “A Professional Spot Welder Made out of a Microwave Transformer

  1. Lol at Arduino.

    More lols at the interface being a PCB rotary switch.

    Other than that, nice build (bar the copper tips – use MIG welder tips).

    Now that that’s out of the way, on with the “microwave ovens are dangerous” posts.

    1. I’ve tried MIG tips however for my build (which is a proper hack sadly) they tend to get stuck in the work piece which a couple of DIY tips made from pure copper doesn’t – or at least less frequently.

      I’ve been pondering if it would be worth trying tungsten-copper tips, have anybody got any experience with those?

      1. I haven’t tried tungsten, I have read they’re not a general purpose tip.

        The MIG tips I’ve got are deoxidized phosphorus copper which I think is the standard, they seems to work. I know some tips are plain copper or even brass. They’re cheap and easy to find. I do find they stick when dirty, wire brush fixes that.

        There is a copper alloy (m-something) that’s used for general purpose spot welding, I need to remember what it is one day and buy some.

    2. For Tony and others that pcb rotary switch seems strange, I have to say that this solution is proper, as next alternative for a micro would be a LCD with menus with buttons to select just timing values. Certainly an overkill. Regarding the blown up Arduino due to spikes, I say that the wiring from Arduino pin to the optocoupler LED should run in right angles and NOT parallel to high current conductors, as high current pulses induce voltage spikes to parallel cable. Otherwise it is a nice built.

  2. Nice hack, Philpem made one a while back but his version used a 600K uF (0.6F) capacitor and some clever switching to tailbite the pulse and dump it into a resistor.

    I tried it using my setup but 1F audio capacitors are not suitable due to the low voltage.
    2*2F might do it though in series but this is unwise and very expen$ive.

  3. building one just to build one is fine……..but if you actually need one on the cheap, harbor freight for $150……

    also, why the hell do we feel the need to put arduinos on everything…..??

    “hey look, an arduino controlled water bottle!!!, it tells me how much water i have left…makes drinking water SOOO much easier!!”

    1. That is what I thought before reading it but he is welding really thin metal to batteries which could be damaged by the heat. If you think you can hold the trigger on the HF one for exactly 100ms then good luck with that. I think the arduino or other small microcontroller makes sense here though I would just buy batteries with tabs already attached.

      1. Sunkko 709A pulse spot welder Battery welding machine would work well for $179 it is hardly worth a diy hack and risking safety for something already manufactured for cheap. neat to say I did this but for myself my hobbies suck away enough time id rather buy the tool than build it if the price isn’t much different like in this case.

    2. Did you actually read the article? The welder uses two pulses, one to pre-heat the metal and then another to weld it. So you actually have three parameters here: (1) pre-heat duration (2) pause duration and (3) weld duration.

      Sure, you could do this with multiple 555s, but a microcontroller will provide much more accurate and consistent timing. If you use a basic MCU (i.e., a bare AT-tiny part or similar) and pushbuttons it will be cheaper than 555s and pots.

    3. The arduino is popular because it allows complex control with a minimum investment of time. You can keep one around (they’re inexpensive enough that having several on hand is easy for most folks) as an incredibly easy-to-program (both programatically and actually pushing code to the device) platform for quickly solving problems.

      Additionally, once you’re done prototyping, if you want the board back it’s easy (so very easy) to migrate to a bare microcontroller (any one of several with varying levels of capability).

      Bitching about it makes you look like a contrary whiner.

    4. I thought this site was called HACKaday, and that we build things, because we are hackers, not off the shelf retail slugs? I think this welder is awesome, and I’ve been welding for several years. I also second the use of an MCU!

      -Fair winds and following Seas

      1. There are two kinds of hackers; those who use tools to build the things they are interested in, and those who are interested in building tools… The poster your arguing with was pointing out that if your the former kind you don’t need to build one of these from scratch since they can be purchased pretty cheaply… To each their own.

        1. Problem with his argument is the HF model wouldn’t do the same task not being a pulse welder as mentioned above however I am one of those that sometimes makes my own tools and sometimes buys them. Time versus money vested and warranties are nice to have.

      2. Seems like every other submission, I see someone boasting that the person could have just bought it instead and that they are dumb because they even tried. What purpose does it serve to post comments like that? This site promotes fabricating things you can buy elsewhere, for the sole purpose gaining insight and knowledge.

        1. There’s a certain kind of person that has trouble imagining other ways of thinking than their own. They tend to respond to things that don’t make sense to them with “that’s pointless” rather than “why was that done?” It’s an oddly common among nerds, particularly engineer types. I think the world would be a better place if people asked more questions and made fewer statements.

          I appreciate the irony of this post.

  4. The loose wires to the “Arduino” unbuffered around a huge transformer that get switched on/off is asking for trouble. So that kills the “Professional” part right there.

    High rate of change in magnetic field is what’s causing the “My Arduino was killed by voltage spikes”. The TVS is only hiding the issue, not solving the actual problem. Read the TVS datasheet carefully to see what the actual clamping voltages is. (it will be higher than 5V!) Surges still get through the TVS up to that voltage and eventually the I/O cell on the AVR will fail.

    – Should use twisted pair to the control circuit. The twisting minimizes the loop area between the pair, so it minimizes the amount of magnetic pick up. Loose wire has a large loop pickup area. Also you want the wire to not be near the AC input and out of the transformer area ASAP. Even then, there will be big surges coming through.
    – I would use a rugged driver that can handle more abuse. Bipolar version of those EIA-485 drivers that can handle +/-10V common mode voltage would be my initial choice along with voltage clamps _at_ the driver and a pair of series resistors before the long twisted pair.

    1. You have to think a bit more on that opto-isolation part and how it is actually implemented… There is already an opto-isolation between the Arduino board and the SCR and obviously that didn’t protect the circuit.

      It is located at the power side, so the cabling is a long magnetic loop that pick up a lot of surges and dump it to the AVR. If you want *actual* protection, you would put an opto-isolator at the “Arduino” side before the long cable and another one at the power circuit with an isolated power supply to break the current loop of any induced current. You would still need to protect the optos.

      Also you want to put that Arduino away from the transformer, high current welding leads and the AC supply too.

  5. I’ve got the HF welder. It has a major deficiency, no Arduino ;-) Trying to produce pulses w/ a toggle switch does not give consistent results. But it is a good transformer and tongs. Yes, you could provide pulses w/ some 555s, but an MCU is easier and will let you collect SPC data on time, current, etc.

    Read the “Fundamentals of Resistance Welding” pdf linked on the builder’s project page and look at the table of currents, times and pulse counts link and you’ll see why an MCU is appropriate.

    Use whatever MCU you prefer. I’m leaning towards the STM32F429 Discovery board because it has a touchscreen.

    This is certainly the best build I’ve seen, but I’d reserve “professional” for a custom metal cabinet to meet commercial product standards. I was a little surprised he didn’t do that given the quality of the design.

    There is certainly a lot of gratuitous application of MCUs, but this project really needs one.

  6. I will admit my ignorance of welding so will one of you gurus tell me if there is finally a little hand welder like in Aliens? I’ve seen the mini propane crack torches but not any mig tig stuff in the store like that. Does it exist?

    1. Closest I am aware of is the Smith Little Torch. But it still needs gas tanks. They can be used with disposable MAPP/OXYGEN, Propare/oxygen (disposabl;e or welding tanks), as well as Acetylene/Oxygen. They are quite popular with jewelers

  7. Variant on inert gas welding using helium (He) as a source, yes could work handheld as well as for repairing some types of glass ie the ionic glass plate used on Iphone 6+.

    Also found an article suggesting that cracked LCDs can also be repaired if the crack is just on the front surface as long as it is done quickly enough before the LCD fluid evaporates.

    Did anyone see that article about using “dead” OLED panels as X-ray detectors?
    Seems that even a bad panel if physically intact will fluoresce under UV and with X-rays even down to 4.7KeV illuminated from the back, maybe useful to some folks here as they are ridiculously high resolution and yes the radiation can be read back by scanning the panel sequentially and monitoring current draw from Vbackplane.

  8. There are purpose made welding tip stocks. They are copper with an amount of chrome. Mallory alloy also used to be used. McMaster Carr has welding electrode stock from 1/8 inch up and it is cheap and lases a long time with all of the proper characteristics. Its what we use in tube assembly.

  9. Interesting that there is no description of removing the magnetic shunt. Are these less common outside the EU, or is the welder intended for use with it in place? (I should have thought the latter unlikely).

  10. Hm, if I understand correctly, this does not reuse the microwave component though, just the transformer? Because if you want to contract cancer or get your bladder to a boil (! really) all you need to do is step into a strong radar source or use a microwave oven without shielding.

    1. I love it when people use phrases like “if I understand correctly…” to attempt the appearance of intelligence. Then they follow that with a question or statement that shows without a doubt that they didn’t even bother to read the original article… Appearance of intelligence vaporised…

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